Section 6m

Engine -Fuel System

Index

Figure Index
Rochester "BC" One barrel
Rochester "2GC" Two barrel
Carter "WCFB" Four barrel
Fuel pump
Air cleaner
Trouble and remedies
Fuel system specifications

Figure Index

The carburetor used on all six cylinder models is a Rochester Model "BC" downdraft carburetor, equipped with an automatic choke. This carburetor presents several distinct features of importance to the car owner and the mechanic. Foremost among these features are:

• Concentric fuel bowl-Regardless of any shift of fuel level in the bowl, the main metering jet is at all times immersed in fuel.
• Centrally located main discharge nozzle-A shift in fuel level has little or no effect on the rate of discharge from the nozzle.
• The main well and support assembly, which contains the main metering jet and the power valve, is attached to the cover and suspended in the float bowl which provides ease in servicing.
• Automatic Choke-Insures proper starting and driving carburetion during cold weather operation.
• A fast idle mechanism, which is in linkage with the choke lever, is an aid to more efficient cold weather warm-up, insuring correct idle speeds during warm-up period.

Idle and Part Throttle System

The carburetor section in figure 1 shows the passages for carburetion during idle and part throttle operating conditions. At idle speed, the throttle valve is almost closed. Below the valve is manifold vacuum. Above the valve is atmospheric pressure. Atmospheric pressure is also present in the balanced-type float chamber. This differential of pressure causes fuel to pass from the float chamber, through the main metering jet, to the idle mixture port via the carburetor crossbar. As the fuel passes through the crossbar, it is mixed with air from two air bleed holes in the crossbar and the mixture calibrated by a restriction tube in the crossbar. Additional amounts of air are mixed with the idle fuel, entering from the float chamber via the float chamber passage and from the carburetor bore above the throttle valve via the auxiliary idle passage. The correct amount of fuel air mixture is then metered to the intake manifold by the adjustable idle mixture needle.

As the throttle valve is opened slightly, the auxiliary idle passage is gradually exposed to manifold vacuum, delivering additional fuel-air mixture to the manifold instead of adding air to the mixture. This permits operation of the idle system to provide sufficient fuel-air mixture for the engine until engine speed and throttle opening are high enough to bring the part throttle system into operation.

The float chamber passage also serves a dual purpose. When the engine is stopped, the fuel in the carburetor is heated by the warm air rising from the exhaust manifold and tends to form a vapor. The float chamber passage permits the idle system to vent, preventing hard starting due to a vapor build-up in the idle system.

Further opening of the throttle valve causes sufficient flow through the carburetor bore to develop venturi action at the main discharge nozzle. The end result of the venturi action is the development of a reduced pressure or partial vacuum and a high air velocity at the main discharge nozzle in the crossbar. This pressure differential and high air velocity causes a fuel flow from the float chamber to the cross crossbar and out through the main discharge nozzle, where it atomizes into the air flow through the small venturi.

The transition from the fuel delivered from the idle passage to the fuel delivered from the main discharge nozzle is a gradual move. The idle passage fuel is slowly reduced as the main discharge nozzle delivers more fuel. Thus, the two systems interact and produce a smooth fuel-air flow at all engine speeds.

Power System

The power system of the Rochester Carburetor acts as a supplementary fuel source automatically coupled to engine demands. It is, in effect, an auxiliary main metering jet.

The power valve is a double step, spring-loaded ball type valve, controlled by a vacuum piston and metered by a power jet. When engine demands increase, the load is reflected in a manifold vacuum decrease. As the vacuum is reduced, the vacuum piston is held in the up position by manifold vacuum above the piston and atmospheric pressure and power valve spring force below the piston. A piston spring tends to push the piston down to unseat the power valve ball. When manifold vacuum drops below 5 inches of mercury, the piston unseats the power valve ball, adding an additional fuel supply line to the main discharge nozzle. The power valve contains a double step arrangement, allowing more fuel to pass the valve as manifold vacuum decreases further.

During high vacuum operation, the power valve is closed, and the main metering jet controls an economical fuel-air ratio. A relief passage from a piston groove leads to the carburetor throat, preventing fuel from passing into the intake manifold under high manifold vacuum.

Accelerating Pump System

The accelerating pump system functions to supply added amounts of fuel for increasing engine power output. The pump plunger, equipped with a spring loaded leather seal, is linked to the throttle control lever. A depression of the accelerator pedal by the driver, calling for more engine output, opens the throttle valve to allow a greater air-fuel intake and depresses the pump plunger to obtain a temporarily richer fuel-air mixture for the accelerating process. When the plunger is depressed, it unseats the discharge ball check valve and forces the fuel into the carburetor throat, spraying it against the inner or small venturi to break up the droplets of fuel for better atomization. The downward travel of the plunger also seats a bypass ball check in the plunger.

In the case of a rapid depression of the accelerator pedal, a spring-loaded feature in the pump linkage allows the linkage to over-run the pump plunger. This prevents an excessive pressure build-up in the accelerating system and smooths out the delivery of the acceleration fuel to the carburetor bore.

When the throttle is closed, the plunger is moved up, the discharge ball check is seated, and fuel is allowed into the pump cylinder by a bypass ball check in the plunger itself. This ball check also serves to eliminate any build-up of fuel vapors in the accelerating system when the engine is stopped.

Float System

The level of fuel in the float bowl directly affects the fuel-air ratio by determining the distance that the fuel must rise to enter the crossbar for the idle and main discharge systems. A low level will produce a lean mixture, a high fuel level, a rich fuel-air ratio. The Rochester Carburetor has a concentric fuel bowl to minimize surge effects on acceleration and deceleration. Twin floats operate a needle valve to control the fuel level.

Automatic Choke System

The automatic choke is designed to insure proper starting and driving during cold weather operation. The system is comprised of a thermostatic coil, choke piston, choke valve and fast idle cam and linkage. It is controlled by a combination of intake manifold vacuum, the offset choke valve, atmospheric temperature and exhaust manifold heat.

The thermostatic coil, which is linked to the choke valve shaft, holds the choke valve closed when the engine is below 85°F.

As the engine is started, air velocity against the offset choke valve causes the valve to open slightly against the torque of the thermostatic coil. In addition, as the engine starts, intake manifold vacuum is applied to the choke piston, which also tends to pull the choke valve open.

As a consequence, the choke valve assumes a position where the torque of the thermostatic coil is balanced against the vacuum pull upon the choke piston and air velocity against the offset choke valve. This causes a regulated air flow into the carburetor which provides a proper mixture during the warm-up period.

During warm-up, the choke piston serves to modify the choking action to compensate for varying engine loads or acceleration. Any acceleration or increased road load decreases the vacuum exerted on the choke piston. This allows the thermostatic coil torque to momentarily increase choke valve closure to provide the engine with a sufficiently richer mixture for acceleration.

As the engine warms up, hot air from the exhaust manifold "stove" is drawn into the thermostatic coil cover by the vacuum behind the choke piston. This hot air causes a rise in temperature causing the bi-metallic coil to slowly relax its tension. Thus, the choke valve is allowed to move gradually to the full open position.

To prevent stalling during the warm-up period, it is necessary to run the engine at an idle speed slightly higher than that for a warm engine. This is accomplished by the fast idle cam (fig. 2) which is linked to the choke valve shaft and holds the throttle valve open sufficiently during the warmup period to give the increased idle RPM until such time as the choke valve moves to the full open position. While the automatic choke is in operation, the driver may wish to advance the throttle to the full wide open position. Since this would decrease vacuum pull on the choke piston, thereby closing the choke valve, it is necessary to provide increased carburetor air flow by opening the choke valve mechanically. To accomplish this, a tang on the throttle lever is made to contact the fast idle cam linkage at wide open throttle position so as to partially open the choke valve. This will also relieve excess choking on starting by allowing more air to enter the carburetor when the engine is cranked with the accelerator held fully depressed.

Care, Maintenance and Adjustments

Because of the simple construction of the "BC" carburetor, it is possible to make all carburetor adjustments without removing the carburetor from the vehicle.

Idle Speed Adjustment

1. With the engine at operating temperature, make sure choke is entirely open and linkage is free. Also make sure throttle linkage is free so that throttle stop screw "A" is against the low step on the fast idle cam (fig. 3).
2. Set parking brake tight, place selector lever in D (Drive) range on Powerglide models, neutral on standard models and then screw in or out to obtain an idling speed of 425 revolutions per minute on Powerglide models. 475 RPM on standard models.

Idle Mixture Adjustment

The idle mixture adjustment should be made to give a smooth idle at the specified idle speed. Missing is an indication of too lean an idle mixture, while "rolling" or "loping" indicates too rich a mixture.

1. With the engine at operating temperature, screw idle adjusting screw "B" in until it seats lightly (fig. 3). CAUTION: Turning adjusting screw in too tight may cause scoring or grooving of the needle.
2. Back off idle adjusting screw 2 1/2 turns.
3. Start engine and allow to idle (engine at operating temperature).
4. Turn screw either way from this position until best idle point is reached. Readjust idle speed and again check mixture adjustment.

Normal setting of the choke is such that the scribed index mark on the choke cover is in line with the long cast mark on the choke housing casting. If it is believed that the indexing is wrong, it may be checked as follows:

1. Remove air cleaner.
2. If engine is hot, remove carburetor from engine and allow to cool uniformly. Removal of the choke cover assembly will accelerate cooling. Carburetor must be normalized to room temperature before attempting to check choke operation. If car has stood for a few hours at room temperature, removal of the carburetor is not necessary.
3. Check choke valve and shaft for free operation.
4. Check room temperature.
5. Reinstall choke cover assembly, rotating clockwise so that thermostatic spring hooks behind choke lever. Rotate cover until choke valve barely closes when the air horn is rapped lightly. For each 5° that room temperature is below 85°F on standard models, 95° on Powerglide models, set cover one (1) mark richer as indicated on choke housing. For each 5° above, set cover one (1) mark leaner. NOTE: Carburetor must be upright on flange and throttle adjusting screw must not touch fast idle cam during above check.
6. Tighten three cover clamp screws. If the indexing was correct, the mark on the cover will align with the long mark on the housing.

Fast Idle Adjustment

No adjustment of the fast idle speed is provided since the steps on the fast idle cam are correctly proportioned to give the correct speed steps above normal speed. It is necessary to have the correct relationship between the fast idle cam position and the choke valve position. To check and adjust this setting, proceed as follows:

1. Place end of idle adjusting screw on the next to highest step of the fast idle cam. Using Gauge J-5120, see if small end of gauge (.073") just slides easily between lower edge of choke valve and bore of carburetor fig. 4.
2. If necessary, bend choke rod using tool J-4552, until required in step 1, is obtained in fig. 5.

Unloader Adjustment

Check and make any necessary correction of the unloader adjustment as follows:

1. Place throttle in wide open position.
2. Using gauge J-5120, see if large end of gauge (.166") just slides freely between lower edge of choke valve and bore of carburetor (fig. 6).
3. If necessary, bend tang of throttle lever with tool J4552 to obtain necessary clearance.

1. Remove carburetor air cleaner.
2. Disconnect fuel line at carburetor cover fitting.
3. Unscrew fitting on choke vacuum tube at cover.
4. Remove line from choke to carburetor "stove" or manifold heat source.
5. Remove 4 cover attaching screws.
6. Disconnect fast idle rod at choke valve lever.
7. Lift cover straight up to prevent damage to floats.
8. With cover fully assembled and cover gasket in position, place assembly up-ended on a flat surface.
9. Place float level gauge, part number 3696192, into position (fig. 7) with tang at center of gauge located in main discharge nozzle of the cover.
10. Bend float arms vertically so that each float just touches top portion of gauge.
11. Carefully bend flat arms horizontally so that each float is centered in the gauge. Tilt assembly 90° each way and check that floats do not touch gauge (fig. 8). This insures that floats will not rub inner sides of float bowl. Recheck level adjustment.

Float Drop Adjustment

To insure sufficient entry of fuel under high speed operation, it is necessary to check and adjust the float drop.

1. With the cover assembly held right side up and floats suspended freely, carefully bend the float tang at rear of float assembly so that the bottom of the float is 1 3/4" below the gasket surface (fig. 9).

Air Horn Installation

Carefully place cover assembly on bowl.

1. Install 4 attaching screws and tighten screws securely.
2. Connect fuel line to carburetor cover fitting.
3. Install choke to stove line.
4. Install and tighten choke vacuum tube.
5. Install fast idle rod to choke lever.
6. Replace carburetor air cleaner and check and adjust, if necessary, idle speed and idle mixture.

Disassembly

1. Remove air cleaner and unscrew the 1/2" brass connector nut on the choke heat tube.
2. Remove three choke cover attaching screws and retainers; then, remove choke cover and thermostatic coil assembly from choke housing.
3. Remove choke cover gasket and baffle plate (fig.10).
4. Remove retainers from each end of choke rod and remove rod.
5. Remove retaining screw at end of choke shaft and carefully pry off choke trip lever, spacing washer and choke lever and collar assembly.
6. Remove two choke valve screws and then remove choke valve.
7. Rotate choke shaft clockwise to free choke piston from housing and then remove piston and choke shaft from carburetor.
8. Remove choke piston pin and piston from choke shaft.
9. Remove two choke housing attaching screws and remove choke housing and gasket from cover.
10. Wash parts in carburetor solvent. Inspect for wear or damage.

Assembly

1. Place new hex fitting packing on choke heat tube. Then place new gasket in position and attach choke housing to cover. Tighten screws securely.
2. Tighten hex fitting on choke housing. Fitting must be tight to prevent loss of vacuum.
3. Inspect choke shaft assembly and piston for evidence of varnish or carbon deposit, clean when necessary. Then assemble choke piston to shaft with pin and install into choke housing. Index piston with piston bore and rotate choke shaft counterclockwise to enter piston into bore.
4. Install choke valve to choke shaft with letters "RP" or "C" facing upward (fig. 11). Center choke valve before tightening screws.
5. Place baffle plate and choke housing gasket into position and install choke cover and thermostatic coil assembly. Rotate cover clockwise until index mark on cover is aligned with long cast mark on the choke housing casting. Install three retainers and screws to choke housing and tighten securely. NOTE: Choke valve should be lightly closed at room temperature (85'F) when index mark on cover and housing are aligned.
6. Place choke lever and collar assembly on end of choke shaft with tang facing choke housing. Install spacing washer and choke trip lever so that tang of trip lever rests on top of tang on choke lever and collar assembly with choke valve closed.
7. Install choke rod and retainer to choke lever and collar assembly and to fast idle cam. The hair pin end of rod must connect to fast idle cam.

NOTE: Check choke valve for free movement.

Automatic Choke Stove

Installation

When the "BC" carburetor is installed on past model vehicles or should the stove be removed for any reason, the following procedure of installation should be followed to assure proper alignment of stove unit.

1. Assemble carburetor to engine manifold, connect carburetor controls, gasoline and vacuum spark control lines.
2. Mount manifold stove assembly on exhaust manifold between No. 1 and No. 2 exhaust ports so that hot air tube connection is offset slightly toward front of engine. Do not tighten retainer screw securely until tube installation is made.
3. Place tapered end of hot air tube into manifold stove connection. Then, by adjusting position of manifold stove on the exhaust manifold, assemble the tube fitting to the carburetor choke housing connection finger tight.
4. After this assembly has been made, tighten the stove retainer screw and the tube fitting securely.

NOTE: If heater is being installed on a replacement manifold, remove point from manifold at heater location before installation.

Throttle Rod Adjustment

The length of the throttle control rod is adjustable to insure wide open throttle with full accelerator pedal depression. The adjustment is made at the bell crank on the left side of the engine block. With the pedal fully depressed and the carburetor throttle fully opened, the swivel should be adjusted on the control rod for free entry into the bell crank. (fig. 12). The swivel should then be given two turns to lengthen the throttle control rod. Assemble the rod to the bell crank.

Major Service Operations

The perfect carburetor delivers the proper gasoline and air ratios for all speeds of the particular engine for which it was designed. By completely disassembling at regular intervals, which will allow cleaning of all parts and passages, the carburetor can be returned to its original condition and it will then deliver the proper ratios as it did when new.

Because of the simplicity of design of the Model "BC" carburetor, few parts are used which will require replacement. Accurate calibration of passages and discharge holes, require that extreme care be taken in cleaning. Use only carburetor solvent and compressed air to clean all passages and passage discharge holes. Never use wire or other pointed instrument to clean as calibration of carburetor will be affected.

Removal

1. Remove air cleaner.
2. Disconnect fuel, vacuum and choke heat lines from carburetor.
3. Disconnect throttle rod from throttle shaft lever.
4. Remove the two carburetor flange to manifold stud nuts and lift carburetor off.

1. Disassemble choke as outlined previously.
2. Disconnect choke vacuum tube at cover.
3. Disconnect fast idle rod at choke lever.
4. Remove four cover screws.
5. Lift cover straight up to prevent damage to floats.
6. Place cover up-ended on flat surface and remove float hinge pin, floats and float needle (fig. 13).
7. Using screw driver of proper width, remove float needle seat and red fiber gasket.
8. Remove main metering jet and power valve assembly from main well support. NOTE: Use care when removing power valve not to lose small spring and ball.
9. Remove main well support attaching screw and remove support. Lift straight up to prevent damage to main well support tube.
10. Lift power piston and spring from cover.
11. Lift air horn gasket from cover.
12. Holding accelerating pump plunger all the way down, remove cotter pin or hairpin retainer from pump link and remove pump link from throttle lever and pump plunger. Pump plunger may now be lifted from bowl.
13. Lift pump spring from pump well.
14. With small needle nose pliers, remove pump discharge guide (fig. 14). Pump discharge spring and ball check will fall from bowl when turned upside down.
15. With bowl upside down, remove 2 throttle. body attaching screws and remove throttle body assembly.
16. Remove idle adjusting needle and spring from throttle body.
17. Figure 15 illustrates carburetor completely disassembled.

1. Wash all metal parts thoroughly in carburetor solvent and dry with compressed air.
2. Check all parts and passages for carbon deposits.
3. Blow out all drilled passages with compressed air and check to make sure they are clean. NOTE: Do not, under any circumstances, use wire or other pointed instrument to clean drilled passages or calibrated holes in carburetor. Holes and passages are carefully calibrated and use of wire or other cleaning instrument will destroy calibration of carburetor.
4. Inspect pump plunger. If the leather or its expanding spring are damaged, in any way, the plunger assembly should be replaced. Shake the plunger to determine if by-pass hall check is free.
5. Check floats for dents and wear on lip and hinge pin. Also check cover for wear in hinge pin holes.
6. Check float needle. If wear is noted on float needle, install new float needle assembly consisting of matched and tested needle and seat and new fibre washer.
7. Check power piston for burrs or other damage. Piston must move freely in cover bore.
8. Check throttle arm for looseness on the shaft and for excessive wear at throttle rod connection.
9. Check throttle shaft for excessive looseness in throttle body. NOTE: Any damage or excessive wear in throttle arm or shaft necessitates replacement of the throttle body assembly. This is due to the close tolerance of throttle valve fit required and the fact that the idle discharge and spark advance holes are drilled in relation to a proper fitting valve.
10. Check the choke valve for freedom of operation in cover.

1. Install idle needle and spring finger-tight in throttle body. As a temporary idle adjustment, back needle out 1% turns.
2. Using a new throttle body gasket, attach bowl to throttle body. Tighten screws evenly and securely.
3. Place pump return spring into pump well and center it by depressing with finger.
4. Install pump plunger and connect pump link to throttle lever and pump rod. Install cotter pin or hairpin retainers at both upper and lower ends.
5. Drop large steel ball into pump discharge cavity of bowl and place bronze color spring on top of ball (fig. 16).
6. Index end of pump discharge guide into bronze color spring and press down until guide is flush with bowl surface.
7. Place new air horn gasket on air horn.
8. Place power piston spring and power piston in air horn cavity and attach main well support to air horn.
9. Install main metering jet and tighten securely.
10. Hold power piston stem down and install power ball, spring and plug and tighten securely. Install float needle seat using new fibre washer and install float needle.
11. Attach float with hinge pin. NOTE: Float tang must face cover.
12. Adjust float setting as outlined under, Minor Service Operations, Float Level Adjustment.
13. Place cover assembly on bowl. Install attaching screws and tighten securely.
14. Install and tighten choke vacuum tube fitting securely.
15. Reconnect fast idle rod at choke lever.

1. Place carburetor in position on manifold studs and install retaining nuts. Tighten evenly and securely.
2. Connect fuel and vacuum lines to carburetor.
3. Connect throttle rod to throttle shaft lever.
4. Connect choke heat tube to automatic choke.
5. Adjust idle speed and mixture as outlined under Care, Maintenance and Adjustments.

General Description

The Rochester Model 2GC two barrel carburetor is standard equipment on all eight cylinder models. While not interchangeable, the carburetors used on Powerglide-equipped models and standard shift models are basically the same, and the description and service operations are identical. The carburetor incorporates the calibrated cluster design.

The cluster casting is the heart of the carburetor; it embodies the small or secondary venturi, the high speed passages, the main well tubes and nozzles, the idle tubes and the calibrated air bleeds for both the low and high speed metering systems, as well as the accelerating pump jets.

When the cluster is removed for service purposes, all of these vital parts can be readily seen, cleaned and examined; the main well tubes and idle tubes are permanently installed in the cluster body by means of a precision pressed fit.

The cluster fits on a platform provided in the body casting of the carburetor so that the main well and idle tubes are suspended in the fuel.

A gasket is used between the cluster casting and the body platform. This method of design and assembly serves to insulate the main well tubes and idle tubes from engine heat, thus reducing heat expansion and percolation spill-over during hot idle periods of operation and during the time the hot engine is not operating.

An external vent with a protective cover to keep out dirt and other foreign matter is located in the center of the bowl cover to provide adequate venting of the unit under all types of operating conditions.

The Model 2GC carburetor functions conventionally, -using the standard six systems of carburetion: Float, Idle, Part Throttle, Power, Pump and Choke. These systems are basically simple and can easily be traced and understood.

The Model 2GC Carburetor is of side bowl construction. It is designed, however, with fuel supply jets and passages submerged enough below the liquid level to provide proper engine operation under all driving conditions.

Operation

Float System

The float system (fig. 17) controls the level of fuel in the carburetor bowl.

Fuel entering the carburetor first travels through the inlet strainer or filter screen to remove particles which might block jets or passages. Then the fuel passes through the needle and seat into the carburetor bowl; flow continues until the rising liquid level raises the float to a position where the valve is closed. Thus the fuel level can be regulated by setting the float to close the valve when the proper level is reached.

The float tang prevents the float from traveling too far downward. A float needle pull clip connecting the float arm to the needle valve keeps the needle from sticking closed in the seat. The needle is equipped with a spring loaded pin which provides a positive shut off under all conditions.

Idle System

The idle system (fig. 18) consists of the idle tubes, idle passages, idle air bleeds, idle adjustment needles and idle discharge holes.

In the idle speed position the throttle valve is cracked slightly open, allowing a small amount of air to pass through between the wall of the carburetor bore and the edge of the throttle valve.

The idle needle hole is in the high vacuum area below the throttle valve, while the fuel bowl is vented to atmospheric pressure. Vacuum can be called a lack of pressure, so a high vacuum area can be spoken of as an area of low pressure. Thus it can be said that there is considerable pressure difference between the normal atmospheric pressure on the fuel in the bowl and the low pressure (or high vacuum) at the idle needle hole.

The fuel and fuel-air mixture is drawn from the highest pressure point to the lowest pressure point and flows from the fuel bowl to the manifold in the following manner:

Fuel is drawn from the fuel bowl through the main metering jets into the main well (shown in fig. 19). It is metered by the idle fuel metering orifice at the lower tip of the idle tube and travels up the idle tube. When the fuel reaches the top of the idle tube, it mixes with air drawn through the primary idle air bleed and the mixture moves through the horizontal idle passage.

The fuel-air mixture next moves down the vertical idle passage to the secondary idle discharge holes located just above the closed throttle valve. Through these holes further air is added to the mixture, which then passes through the idle needle hole.

In addition to this mixture of fuel and air, there is air entering the bore through the slightly open throttle valve; for smooth operation, the air from the bore and the fuel air mixture from the idle needle hole must combine to form the correct final mixture for curb idle engine speed.

The position of the idle adjustment needle governs the amount of air-fuel mixture admitted to the carburetor bore.

Except for this variable at the idle adjustment needle, the idle system is specifically calibrated for idle engine speed.

Part Throttle System

As the throttle valve is opened, there is a change in pressure differential points.

Initial opening of the valve progressively exposes the secondary idle discharge holes to manifold vacuum and the air stream with the result that they deliver additional air-fuel mixture for fast idle engine requirements.

Further opening of the throttle valve increases the speed of the air stream passing through the venturi, thus lowering the pressure (or raising the vacuum) in the small venturi area of the carburetor bore (fig. 19). At the same time, the edge of the throttle valve is moved away from the wall of the bore, progressively reducing the vacuum and thus the mixture flow at the idle discharge holes.

Since the low pressure point is now in the small venturi area, fuel and fuel air mixture will be drawn from the fuel bowl through the main metering system to the venturi.

The fuel passes through the main metering jet into the main well, where it rises in the main well tube. Air entering through the main well air bleeds in the cluster is mixed with the fuel through the main well tube vents. The mixture continues up the main well tube through the nozzle, where more air is added. The mixture flows through the high speed passage to the small venturi, mixes with additional air and moves on to the bore of the carburetor, through the intake manifold, and into the cylinder as a final mixture for part throttle operation.

Permanent jets and air bleeds calibrate the main metering system for proper part throttle operation.

Power System

The power system provides additional fuel for heavy load and high speed engine requirements.

A spring loaded power piston, controlled by vacuum, regulates the power valve to supply additional fuel according to engine speed and load.

The power piston vacuum channel is open to manifold vacuum beneath the throttle valves; thus the vacuum in the channel rises and falls with manifold vacuum.

During idle and part throttle operation, the manifold vacuum in the channel is normally high enough to hold the power piston in the fully raised position against the tension of the spring. As the manifold vacuum drops with load, the calibrated spring forces the piston down against the power valve, to open it and allow additional fuel flow through the calibrated power restrictions into the main wells.

A two-step valve allows a partial increase in fuel flow for low speed-low vacuum without over-enrichment, as the power valve is opened; at full throttle position, the power valve is fully opened to permit maximum calibrated fuel flow from the power system.

As the load decreases, manifold vacuum increases. The increasing vacuum pull on the piston gradually overcomes the spring tension and returns the power piston to its original raised position, with the valve fully closed.

Pump System

Extra fuel for smooth, quick acceleration is supplied by a double spring pump plunger (fig. 20). The combination of the top and bottom springs is calibrated to move the plunger in such a manner that a smooth, sustained charge of fuel is delivered for acceleration.

The fuel passes from the bowl past the pump plunger ball check into the pump well on the intake stroke of the plunger. When the plunger is pushed downward for acceleration, the fuel is forced up the pump discharge passage.

The pressure of the fuel lifts the pump outlet ball check from its seat and the fuel passes on through the pump jets in the cluster, where it is sprayed into the venturi and delivered to the engine.

The pump plunger head embodies a unique ball check and seat, designed to eliminate fuel percolation in the pump system. When the engine is idling or not operating, excessive fuel vapors in the pump well rise through the plunger head and by-pass the ball, then circulate into the fuel bowl, which is vented to the atmosphere.

Without this feature, vapor pressure in the pump system might force fuel from the pump well into the engine, causing hard hot starting because of excess fuel in the manifold or poor initial acceleration due to vapor in the pump system.

Choke System

For cold engine operation, a rich mixture at the carburetor is required, so that a combustible mixture remains to be drawn into the cylinder after condensation of much of the fuel vapor on the cold engine parts. The function of the choke system is to subject all fuel outlets in the bore of the carburetor to high vacuum while restricting the intake of air, thus drawing into the engine the required rich mixture.

The Model 2GC Carburetor employs the newly designed Rochester Multistage Balanced Piston automatic choke system, to insure proper starting and driving during cold weather operation (fig. 21).

The choke system includes a thermostatic coil, housing, choke piston, choke valve and fast idle cam and linkage. It is controlled by a combination of intake manifold vacuum, air velocity against the offset choke valve, atmospheric temperature and exhaust manifold heat.

The thermostatic coil, which is attached to the choke housing cover acts to hold the choke valve closed when the engine is cold.

The offset choke valve is first slightly opened by a combination of manifold vacuum on the choke piston and air velocity against the offset choke valve.

In the first choking stage, manifold vacuum is applied to the choke piston through a vacuum slot in the housing. This vacuum pulls the piston to help open the choke valve against the thermostatic coil torque. The piston moves in the housing to a point where the piston blocks the vacuum slot; at this point there is very small amount of vacuum pull on the piston and further choke valve opening is primarily the function of the thermostatic coil.

In the second stage, the coil is gradually heated by air drawn from the exhaust manifold "stove," through the center of the thermostatic coil cover, then through a calibrated vacuum by-pass into the main vacuum passage. The calibrated restriction of the vacuum by-pass slows the flow of air through the coil, so that the heating is gradual. Baffle plate serves to distribute the heat from its entering point at the center of the coil throughout the choke housing, to prevent a "hot spot" in the coil center.

The coil "relaxes" as it is heated and the piston moves in the housing until the shoulder of the "slabbed" portion uncovers the edge of the vacuum slot. One side of the piston is "slabbed" cut away, so that vacuum from the slot can draw air directly from the choke housing, thus allowing a greater flow of heat through the coils for the rest of the opening operation.

The thermostatic coil controls the majority the choking action and coils with high thermal activity can be chosen to best fit engine characteristics. Also, low manifold vacuum (during acceleration or load) cannot allow the choke partially close as much as often happens in conventional vacuum controlled choke system.

The choke system uses a conventional fast idle cam and linkage to maintain sufficient engine speed for cold operation.

The carburetor is also equipped with a mechanical "unloader" to eliminate the possibility of choke closing during heavy load or acceleration At wide open throttle, the throttle lever lifts tang on the fast idle cam and restricts the choke from closing past a certain point. This feature particularly useful in preventing excess choking when the engine is cranked with the throttle wide open.

In addition, the unloader also eliminates possibility of the choke sticking closed, or closing during heavy load or acceleration due to low vacuum on the piston.

Care, Maintenance and Adjustments

The carburetors are carefully designed and calibrated to meet engine requirements. They are tested and adjusted at the factory to meet specifications. It is a common practice to blame the carburetor for many engine problems, and before making carburetor adjustments, there are several items to be checked.

Preliminary Checks

1. Thoroughly warm-up engine. If the engine is cold, allow to run for at least 15 minutes.
2. Inspect torque of carburetor to intake manifold bolts and intake manifold to cylinder head bolts to exclude the possibility of air leaks.
3. Inspect manifold heat control valve for freedom of action and correct spring tension. NOTE: For float level and pump lever operations, warm-up is not required.

1. Connect tachometer and vacuum gauge to engine. Set parking brake and place transmission in neutral.
2. With a thoroughly warmed-up engine, check to see that choke is fully off and carburetor is on slow idle.
3. Start engine and allow to idle. Adjust idle speed (fig. 22) to give 475 R.P.M.
4. On Powerglide models, move selector lever to Drive Range. Adjust each idle mixture screw (fig. 23) separately to give peak vacuum and R.P.M. indications on tachometer and vacuum gauge. CAUTION: Do not turn idle mixture screws tightly against stop or damage to needle seat will result.
5. If necessary, readjust engine idle to 475 R.P.M. on standard shift models, 425 R.P.M. on Powerglide models with selector lever in Drive Range. Readjust idle mixture as outlined in Step 4.
6. Shut off engine and remove tachometer and vacuum gauge.
7. Road test vehicle to check performance.

The length of the throttle linkage is adjustable to assure wide-open throttle with full accelerator pedal depression. To check, depress accelerator pedal fully and check to see if throttle is wide open. If not, adjust threaded swivel at throttle lever to suit. With the accelerator pedal fully depressed and the carburetor throttle valve fully open (through detent on Powerglide models) the threaded swivel should be adjusted for free entry into the throttle lever (fig. 24). The swivel should then be turned two full turns to lengthen the control rod.

Float Level and Drop Adjustment

1. Remove bowl cover with gasket from carburetor as described under Major Service Operations.
2. Invert the cover on a flat surface. Place float gauge J-5915 over float as shown in fig. 25.
3. Bend float hinge arm as required until the highest part of the float just clears the gauge step. The scale dimension, bottom of float to gasket, is 1 9/64".
4. Hold bowl in an upright position and measure the distance from the gasket to the bottom of the float, as shown in fig. 26. This dimension should be 1 29/32". Bend the tang at the end of the float hinge arm to obtain the correct drop.
5. Install the bowl cover as outlined under Major Service Operations.
6. Readjust idle mixture.

1. Back out idle speed screw.
2. Hold throttle valve completely closed and check position with gauge J-5915 (fig. 22 and fig. 27).
3. Adjustment is made by bending accelerator rod at lower end.

Automatic Choke Adjustment

Normal setting of the choke is such that the scribed index mark on the cover is in line with the long cast mark on the choke housing casting. If it is believed that the indexing is wrong, it may be checked as follows:

1. Remove air cleaner.
2. If engine is hot, remove carburetor from engine and allow to cool uniformly. Removal of the choke cover assembly will accelerate cooling. Carburetor must be normalized to room temperature before attempting to check choke operation. If car has stood for a few hours at room temperature, removal of the carburetor is not necessary.
3. Check choke valve and shaft for free operation.
4. Check room temperature.
5. Reinstall choke cover assembly rotating clockwise so the thermostat spring hooks behind choke lever. Set cover index mark to long index mark of choke housing if room temperature is 75°; set one (1) mark leaner for each so that temperature is below 75° or one (1) mark richer for each 5° that temperature is above 75°. Choke valve should close when air horn is vibrated or rapped lightly. NOTE: Carburetor must be upright on flange and throttle adjusting screw must not touch fast idle cam during above check.
6. If original setting was correct, reset cover index mark to long index mark on choke housing and tighten three cover screws. If above check indicates need for changing original cover setting, make necessary correction and tighten three cover screws.

No adjustment of the fast idle speed is provided since the steps on the fast idle cam are correctly proportioned to give the correct speed steps above normal idle speed. It is necessary, however, to have the correct relationship between the fast idle cam position and the choke valve position. To check and adjust this setting, proceed as follows:

1. Place end of idle adjusting screw on the next to highest step of the fast idle cam. Using gauge J-5921, see if small end of gauge just slides easily between upper edge of choke valve and bore of carburetor (fig. 28). NOTE: Gauge must be held vertically.
2. If necessary, bend choke rod until required clearance as measured in step 1 is obtained.

Unloader Adjustment

Check and make any necessary correction of the unloader adjustment as follows:

1. Place throttle in wide open position.
2. Using gauge J-5921, see if large end of gauge just slides freely between upper edge of choke valve and bore of carburetor (fig. 29). NOTE: Gauge must be held vertically .
3. If necessary, bend tang of throttle lever to obtain necessary clearance.

MAJOR SERVICE OPERATIONS

REMOVAL

1. Remove air cleaner wing nut, air cleaner, gasket and stud.
2. Disconnect vacuum line, spark control line, fuel line and choke heat tube.
3. Disconnect throttle rod at carburetor and remove throttle return spring. (On Powerglide models, disconnect transmission control rod from throttle lever.)
4. Remove four nuts and washers retaining carburetor to manifold. (On overdrive models, lay kick-down switch aside without disconnecting wires.)
5. Lift carburetor off manifold.
6. Remove and discard carburetor to manifold gasket.

Flooding, stumble on acceleration and other performance complaints are, in many instances, caused by the presence of dirt, water or other foreign matter in the carburetor. To aid in diagnosing the cause of the complaint, the carburetor should be carefully removed from the engine without draining the fuel from the howl. The contents of the fuel bowl may then be examined for contamination as the carburetor is disassembled.

The following is a step-by-step sequence by which the Rochester Model 2 GC Carburetor may be completely disassembled and reassembled. Adjustments may be made and various parts of the carburetor may be serviced without completely disassembling the entire unit.

Choke

1. Remove the three choke cover attaching screws and retainers, then remove choke cover and coil assembly from carburetor.
2. Remove choke cover gasket and baffle plate.
3. Remove retaining screw at end of choke shaft (fig. 30) and carefully pry off choke trip lever, and fast idle link and lever. Lever can be removed from link by turning until slot in lever will pass over tang on link.
4. Remove two choke valve screws, then remove choke valve.
5. Rotate choke shaft counterclockwise to free choke piston from housing, then pull piston and choke shaft from carburetor.
6. Remove two choke housing attaching screws. Choke housing and gasket may now be removed from air horn assembly.

1. Disconnect pump link from throttle lever by removing retainer. Link can be removed completely by rotating until it clears pump lever.
2. Remove eight cover screws and lift cover from bowl.
3. Place upended cover on flat surface. Remove float hinge pin and lift float assembly from cover. Float needle may now be removed from float.
4. Remove float needle seat and gasket with wide blade screw driver and remove filter screen.
5. Remove power piston by depressing shaft and allowing spring to snap, thus forcing piston from casting.
6. Remove retainer on pump plunger shaft, remove plunger assembly from pump arm. The pump lever and shaft may be removed by loosening set screw on inner arm and removing outer lever and shaft.
7. Remove the cover gasket. Figure 31 shows the choke and bowl cover exploded. NOTE: The pump plunger may be further disassembled by compressing the spring and removing the retainer.

1. Remove pump plunger return spring from pump well.
2. Remove main metering jets and power valve.
3. Remove three screws on top of cluster, after which cluster and gasket may be removed.
4. Using a pair of long nose pliers, remove the pump discharge spring retainer. Then the spring and check ball may also be removed.
5. Upend carburetor and remove three large bowl to throttle body attaching screws. Throttle body and gasket may now be removed.
6. Remove fast idle cam.
7. Remove idle adjusting needles and springs from throttle body. Figure 32 shows the bowl and throttle body exploded.

Dirt, gum, water or carbon contamination in or on the exterior moving parts of a carburetor are often responsible for unsatisfactory performance. For this reason, efficient carburetion depends upon careful cleaning and inspection while servicing.

1. Thoroughly clean carburetor castings and metal parts in clean cleaning solvent. CAUTION: Choke coil and housing and pump plunger should not be immersed in solvent. Clean pump plunger in clean gasoline only. DO NOT SOAK AIR HORN ASSEMBLY IN CLEANER OR SOLVENT FOR MORE THAN ONE HALF HOUR IF CHOKE PISTON HOUSING HAS NOT BEEN REMOVED.
2. Blow all passages in castings dry with compressed air and blow off all parts until they are dry. CAUTION: Do not pass drills or wires through calibrated jets or passages as this may enlarge orifice and seriously affect carburetor calibration.
3. Check all parts for wear. If wear is noted, defective parts must be replaced. Note especially the following:
   • Check float needle and seat for wear. If wear is noted the assembly must be replaced.
   • Check float lip for wear and float for dents. Check floats for leaks by shaking.
   • Check throttle and choke shaft bores in throttle body and cover castings for wear or out of round.
   • Inspect idle adjusting needles for burrs or ridges. Such a condition requires replacement.
   • If wear is noted on steps of fast idle cam, it should be replaced as it may upset engine idle speed during the choking period.
   • Inspect pump plunger leather. Replace plunger if leather is damaged.
4. Inspect gaskets to see if they appear hard or brittle or if the edges are torn or distorted. If any such condition is noted they must be replaced.
5. Check filter screen for dirt or lint. Clean and if it is distorted or remains plugged, replace.
6. If for any reason parts have become loose or damaged in the cluster casting, it must be replaced.

Throttle Body

1. Screw idle adjusting needles and springs into throttle body until finger tight. Back out screw 1 1/2 turns as a temporary idle adjustment. CAUTION: Do not force needle against seat or damage will result.
2. Upend bowl, place new throttle body gasket in position and attach throttle body to bowl. Tighten screws evenly and securely.

Bowl

1. Install fast idle cam.
2. Drop pump discharge check ball into discharge hole. Ball is 3/16" diameter steel. Replace spring and retainer.
3. Replace cluster and gasket, tighten screw evenly and securely. Make certain center screw is fitted with red fibre gasket.
4. Replace main metering jets and power valve gasket and power valve. Figure 33 shows the bowl and throttle body at this stage of assembly.
5. Install pump return spring, pressing with finger to center it in pump well.

1. Replace pump lever assembly.
2. Install filter screen, float needle seat and gasket, using wide blade screw driver.
3. Replace power piston in vacuum cavity; piston should travel freely in cavity. Lightly stake retainer in place.
4. Attach plunger shaft with retainer, with shaft end pointing inward.
5. Install cover gasket.
6. Attach needle to float, carefully position float and insert float hinge pin. Figure 34 shows the bowl cover assembled.
7. Adjust float as previously outlined.
8. Place cover on bowl, making certain that accelerator pump plunger is positioned and will move freely. Raise cover and lower straight down to insure proper installation.
9. Install and tighten 8 cover screws evenly and securely.
10. Install pump link and retainer.

1. Place new gasket into position and attach choke housing to cover. Tighten screws securely.
2. Place shaft in choke housing and rotate clockwise so that piston rides in bore in housing.
3. Install choke valve on choke shaft with letters "RP" facing upward. Center choke valve before tightening screws.
4. Place baffle plate and choke housing gasket into position and install choke coil and cover. Rotate cover counterclockwise until index marks on cover and housing are aligned. Attach three retainers and screws to choke housing and tighten securely. NOTE: Choke valve should be slightly closed at room temperature (75 degrees F) when index mark on cover and housing are aligned.
5. Replace link in fast idle cam and choke lever, place choke lever on cover with the tang facing outward and toward the pump lever. Install trip lever so that tang of trip lever is under tang of choke lever.

It is good shop practice to fill the carburetor bowl before installing the carburetor. This reduces the strain on the starting motor and battery and reduces the possibility of backfiring while attempting to start the engine. A fuel pump clamped to the bench, a small supply of fuel and the necessary fittings enable the carburetor to be filled and the operation of the float and intake needle and seat to be checked. Operate the throttle several times and check the discharge from the pump jets before installing the carburetor.

INSTALLATION

1. Be certain throttle body and intake manifold gasket surfaces are clean.
2. Install new carburetor to manifold gasket over manifold carburetor studs.
3. Start spark control pipe fitting into carburetor fitting.
4. Lower carburetor onto manifold studs, choke housing to right side of vehicle.
5. Install and tighten securely four washers and nuts, using a short, open end wrench. (On overdrive models, install and adjust kickdown switch, see Transmission Section 7.) NOTE: Copper washers are used on two front studs.
6. Tighten spark control pipe fitting and connect and tighten choke heat tube, vacuum line and fuel line.
7. Install throttle rod and throttle return spring. (On Powerglide models, install transmission control rod. )
8. Install air cleaner gasket, stud, air cleaner and wing nut. Tighten securely.
9. Adjust idle speed and mixture.

"Classic Data Note: For illustrations of WCFB please refer to 1956 Engine Fuel Section".

General Description and Operation
Care, Maintenance and Adjustments
Float Adjustments
Pump Adjustment
Metering Rod Adjustment
Vapor Vent Adjustment
Fast Idle Cam Clearance Adjustment
Unloader Adjustment
Lockout Adjustment
Fast Idle Adjustment
Idle Mixture Adjustment
Major Service Operations
Disassembly
Air Horn
Carburetor Body
Throttle Flange
Cleaning and Inspection
Assembly
Throttle Flange
Carburetor Body
Air Horn
Carter WCFB Four Barrel

General Description and Operation

A Carter WCFB carburetor is available as optional equipment on 8-cylinder engines. This carburetor is used in conjunction with a dual exhaust system when higher engine performance is desired.

The Carter Model WCFB carburetor is basically two (2) dual carburetors contained in one assembly. The section containing the metering rods, accelerating pump and choke is termed the primary side of the carburetor, the other section, the secondary side. It has five (5) conventional circuits as have been used in previous carburetors. They are:

2-Float Circuits

1-Low Speed Circuit

2-High Speed Circuits

1-Pump Circuit

1-Climatic Control (choke) Circuit

FLOAT CIRCUITS

The purpose of the float circuits is to maintain an adequate supply of fuel at the proper level in the bowls for use by the low speed, high speed, pump and choke circuits. Primary and secondary bowls are separated by a partition. The fuel line connection is on the primary side. Fuel is supplied to the primary and secondary intake needles and seats through a passage in the bowl cover, located at the fuel inlet.

Setting the floats to specifications assures an adequate supply of fuel in the bowls for all operating conditions. Float adjustments must be made with the bowl cover gaskets removed and should be checked vertically (specified distance between bowl cover and bottom of floats) and laterally (sides of floats should just clear the arms of gauge). Correct lateral adjustment is important. If the floats are misaligned, they may bind or drag against the inner walls of the bowl.

Intake needles and seats are carefully matched during manufacture. Do not use the primary needle in the secondary seat or vice-versa. To avoid unnecessary bending, floats should be reinstalled in their original positions and then adjusted.

The bowls are vented to the inside of the air horn. Bowl vents are calibrated to provide proper air pressure above the fuel at all times. To assure a positive seal, always use a new bowl cover gasket and a new dust cover gasket when reassembling. An air leak at these points can result in a mileage complaint.

A connecting passage along the outside of the body effects a balance of the fuel levels and air pressures between the two bowls.

LOW SPEED CIRCUITS

Fuel for idle and early part throttle operation is metered through the low speed circuit.

Fuel enters the idle wells through the metering rod jets on the primary side of the carburetor. No idle system is used in the secondary side of the carburetor.

The low speed jets measure the amount of fuel for idle and early part throttle operation. The air by-pass, economizers, and idle bleeds are carefully calibrated and serve to break up the liquid fuel and mix it with air as it moves through the passages to the idle ports and idle adjustment needle ports. Turning the idle adjustment needles toward their seats reduces the quantity of fuel mixture supplied by the idle circuit.

The idle ports are slot shaped, as the throttle valves are opened more of the idle ports are uncovered, allowing a greater quantity of fuel and air mixture to enter the carburetor bores. The secondary throttle valves remain seated at idle.

The vapor vent valve operated by the arm on the countershaft provides a vent for fuel vapors to escape from the carburetor bowls to the outside at idle and when engine is not in operation.

Air leakage at the gasketed surface surrounding the low speed mixture passages or between the flange and manifold may cause poor idle and low speed operation. Always use new gaskets.

All by-pass, bleeds, economizers, idle ports, idle adjustment screw ports, as well as the boxes of the flange must be clean and free of carbon. Obstructions will cause poor low speed engine operation. Worn or damaged idle adjustment screws or low speed jets should be replaced.

HIGH SPEED CIRCUITS

Fuel for part throttle and full throttle operation is supplied through the high speed circuits. Main discharge nozzles are permanently installed and must not be removed in service.

Primary Side

The position of the metering rods in the metering rod jets control the amount of fuel flowing in the high speed circuit of the primary side of the carburetor. The position of the metering rods is dual controlled; mechanically by movement of the throttle, and by manifold vacuum applied to the vacuum piston on the vacumeter link.

Mechanical Metering Rod Action

During part throttle operation, manifold vacuum pulls the vacumeter piston, link and metering rod assembly down holding the vacumeter link against the metering rod countershaft arm. Movement of the metering rods will then be controlled by the metering rod countershaft arm which is connected to the throttle shaft. This is true at all times that the vacuum under the piston is strong enough to overcome the tension of the vacumeter spring.

Vacuum Metering Action

Under any operating condition (acceleration, hill climbing, etc.), when the tension of the vacumeter spring overcomes the pull of vacuum under the piston, the metering rods will move toward their wide-open throttle or power position.

Secondary Side

Fuel for the high speed circuit of the secondary side is metered at the main metering jets (no metering rods used).

Throttle valves in the secondary side remain closed until the primary throttle valves have been opened a predetermined amount. They arrive at wide open throttle position at the same time as the primary valves. This is accomplished by linkage between the throttle levers.

Secondary throttle valves are locked closer during choke operation to insure faster cold engine starting and warm-up.

Anti-Percolator

To prevent vapor bubbles in the nozzle passages and low speed wells from forcing fuel out of the nozzles, anti-percolator and calibrated plugs and bushings are used. Their purpose is to vent the vapors and relieve the pressure before it is sufficient to push the fuel out of the nozzles and into the intake manifold. Anti-percolator plugs and bushings are permanently installed and must not be removed in service.

PUMP CIRCUIT

The pump circuit is located only in the primary side of the carburetor. The accelerating pump circuit provides the measured amount of fuel necessary to insure smooth engine operation during acceleration at speeds below approximately 30 MPH.

When the throttle is closed the pump plunger moves upward in its cylinder and fuel is drawn into the pump cylinder through the inlet passage. The discharge needle is seated at this time to prevent air being drawn into the cylinder. When the throttle is opened the pump plunger moves downward forcing fuel out through the discharge passage, past the discharge needle, and out of the pump jets. When the plunger moves downward the inlet valve is closed preventing fuel from being forced back into the bowl.

If the throttle is opened suddenly the pump spring will be compressed by the plunger shaft telescoping, resulting in a smoother pump discharge of longer duration.

At speeds above approximately 30 MPH pump discharge is no longer necessary to insure smooth acceleration. When the throttle valves are opened a predetermined amount, the pump plunger bottoms in the pump cylinder eliminating pump discharge.

CHOKE CIRCUIT

The climatic control circuits provides a correct mixture necessary for quick cold engine starting and warm-up.

When the engine is cold, tension of the thermostatic coil holds the choke valve closed. When the engine is started, air velocity against the offset choke valve causes the valve to open slightly against the thermostatic coil tension. Intake manifold vacuum applied to the choke piston also tends to pull the choke valve open. The choke valve assumes a position where tension of the thermostatic coil is balanced by the pull of vacuum on the piston and air velocity on the offset choke valve.

When the engine starts, slots located in the sides of the choke piston cylinder are uncovered allowing intake manifold vacuum to draw warm air from the hot air tube, located in the exhaust manifold, through the climatic control housing. The flow of warm air in turn heats the thermostatic coil and causes it to lose some of its tension. The thermostatic coil loses its tension gradually until the choke valve reaches wide open position.

When the engine is accelerated during the warm-up period, the corresponding drop in manifold vacuum allows the thermostatic coil to momentarily close the choke, providing a richer mixture.

During the warm-up period it is necessary to provide a fast idle speed to prevent engine stalling. This is accomplished by a fast idle cam which is rotated by a connector rod attached to the choke shaft. The fast idle cam prevents the primary throttle valves from returning to a normal warm engine idle position while the climatic control is in operation.

During the starting period if the engine becomes flooded, the choke valve can be partially opened manually. This can be accomplished by depressing the accelerator pedal to the floor and engaging the starter. The projection on the throttle lever (unloader) will rotate the fast idle cam and in turn partially open the choke valve.

Care, Maintenance and Adjustments

FLOAT ADJUSTMENTS

The float adjustments are described and made during assembly of the bowl cover. The remaining adjustments are made in the following sequence.

PUMP ADJUSTMENTS

1. Install pump connector link in outer hole (long stroke) of pump arm, with ends extending toward countershaft arm.
2. Back out throttle lever set screw until throttle valves seat in bores of carburetor.
3. Hold straight edge across top of dust cover boss at pump arm.NOTE: The flat on top of pump arm should be parallel to straight edge.
4. Adjust by bending throttle connector rod at lower angle using tool J-5496.

METERING ROD ADJUSTMENT

Metering Rod Adjustment must be made after completing the pump adjustment using the following procedure: NOTE: No metering rod gauges are necessary.

1. Back out throttle lever set screw to allow throttle valve to seat in bores of carburetor and loosen metering rod arm clamp screw.
2. With metering rods in place, press down on vacumeter link until metering rods bottom in carburetor body casting.
3. With rods in downward position and throttle valves seated, revolve metering rod arm until finger on arm contacts lip of vacumeter link. Hold in place and carefully tighten clamp screw.

BOWL VAPOR VENT ADJUSTMENT

1. After completing pump and metering rod adjustment install dust cover and dust cover gasket.
2. Back out throttle lever set screw to allow throttle valves to seat in bores of carburetor.
3. Using gauge (J-6039) between lower edge of bowl vapor vent valve and dust cover, there should be 1 1/16" distance.
4. If necessary to adjust, remove dust cover and bend vapor vent arm.

1. Loosen choke lever clamp screw on choke shaft.
2. Insert gauge (.020-.030) J-1388 between lip of fast idle cam and boss of flange casting. Hold choke valve tightly closed and take slack out of linkage by pressing choke lever toward closed position.
3. Hold in place and tighten clamp screw.
4. With choke valve tightly closed tighten fast idle adjusting screw until there is .015 opening (using gauge KMO-657) between throttle valve and bore of carburetor side opposite idle port. CAUTION: Be sure fast idle adjusting screw is on high step of cam during this adjustment. NOTE: Fast idle adjustment may be made on the vehicle using the following procedure:
   • With engine and transmission warm, place shift lever in neutral and set emergency brake.
   • Rotate fast idle cam so fast idle screw rests on high step of cam.
   • Adjust fast idle screw to obtain 1600 R.P.M.

UNLOADER ADJUSTMENT

1. With gauge J-818-3 check clearance between upper edge of choke valve and inner wall of bowl cover. This should be 3/16".
2. If adjustment is necessary, bend unloader lip on throttle shaft lever using bending tool J-1137.

SECONDARY THROTTLE LEVER

ADJUSTMENT

1. Determine that the primary and secondary throttle valves reach wide open position at the same time.
2. If necessary to adjust, bend throttle operating rod at upper angle with bending tool J-5496.

SECONDARY THROTTLE LOCK OUT

ADJUSTMENT

1. After completing fast idle and secondary throttle lever adjustments, crack throttle valves and hold choke valve closed, then close throttle.
2. If adjustment is correct, tang on secondary throttle lever should freely engage in notch of lock-out dog. If out of adjustment, bend tang on secondary throttle lever.

Flooding, stumble on acceleration and other performance complaints are, in many instances, caused by the presence of dirt, water or other foreign matter in the carburetor. To aid in diagnosing the cause of the complaint, the carburetor should be carefully removed from the engine without draining the fuel from the bowl. The contents of the fuel bowl may then be examined for contamination as the carburetor is disassembled.

CAUTION: Whenever the carburetor is removed from the engine, care must be exercised to avoid damaging the throttle valves, as the lower edge of the valves project below the throttle flange when the valves are in the open position.

DISASSEMBLY

Bowl Cover

1. Remove gasoline strainer, nut, screen, and gasket assemblies from primary and secondary sides.
2. Remove throttle connector rod at both ends.
3. Remove choke connector rod at both ends.
4. Remove 2 metering rod housing dust cover attaching screws, dust cover and gasket.
5. Loosen, but do not remove screw holding the pump operating lever to pump countershaft.
6. Remove atmospheric vent arm screw and vent arm.
7. Loosen, but do not remove metering rod arm screw.
8. Slide pump countershaft and lever assembly from bowl cover assembly.
9. Remove pump arm and link assembly and metering rod arm.
10. Remove both metering rods and metering rod discs.
11. Remove choke lever from choke shaft.
12. Remove 3 choke coil housing screws and retainers.
13. Remove choke coil housing, gasket and then the baffle plate. NOTE: Under normal service the carburetor bowl cover may be cleaned without further disassembly. If complete disassembly is necessary, perform the remaining operations.
14. File off staked end of choke valve screws. Remove screws and valve.
15. Rotate choke shaft counter-clockwise, then remove shaft and piston assembly.
16. Remove 3 self tapping screws, choke piston housing and gasket.
17. Remove 16 bowl cover attaching screws.
18. Carefully remove bowl cover assembly with gasket and attached parts by lifting straight up from carburetor body assembly. To avoid bending floats, be sure bowl cover gasket is not sticking to body casting.
19. Remove primary float hinge pin, float assembly and intake needle. IMPORTANT: Mark and group float assemblies with needle and needle seat together as units. Extreme care should be taken to avoid mixing needles and seats.
20. Remove secondary float hinge pin, float assembly and intake needle in the same manner.
21. Remove primary needle seat and gasket.
22. Remove secondary needle seat and gasket.
23. Remove vacumeter piston and vacumeter piston link.
24. Remove gasket from bowl cover.

1. Remove pump plunger assembly and lower pump spring.
2. Remove vacumeter spring. NOTE: Check the fuel in the bowl for contamination by dirt, water, gum or other foreign matter, then drain fuel from bowl.
3. Remove pump jet cluster attaching screw, then remove cluster and gasket.
4. Invert carburetor and remove small pump (brass) discharge needle.
5. Remove pump inlet ball retainer and check ball from bottom of pump cylinder.
6. Remove pump passage screw plug.
7. Remove 2 primary metering rod jets (located on pump cylinder side of carburetor).
8. Remove 2 secondary main jets. NOTE: Primary metering rod jets have different openings than the secondary main jets. Never mix these jets.
9. Remove the low speed jet tubes (primary side).
10. Loosen the 6 throttle flange to carburetor body attaching screws.
11. Remove throttle flange from body and remove screws.
12. Remove gasket from carburetor body.

1. Remove idle adjusting needles with springs. NOTE: Under normal service the carburetor flange may be cleaned without further disassembly. If complete disassembly is necessary, perform the remaining operations.
2. Remove fast idle cam screw and fast idle cam assembly.
3. Remove primary to secondary connector rod pin springs and washers, then remove rod.
4. Remove primary throttle shaft screw and washer.
5. Remove primary throttle levers and spring as an assembly.
6. Remove primary throttle shaft spring thrust washer.
7. Remove secondary throttle shaft screw and washer.
8. Remove secondary throttle lever, and secondary throttle return spring.
9. File off staked ends of throttle valve attaching screws and remove screws and throttle valves from the four bores.
10. Remove primary and secondary throttle shafts.
11. Remove idle speed screw.

1. Wash all parts in carburetor cleaning solution except choke coil housing assembly and pump plunger.
   • Choke coil housing assembly should he cleaned in gasoline.
2. Inspect holes in all operating levers and castings for excessive wear.
3. Inspect bearing surfaces of all shafts for excessive wear. NOTE: If excessive wear is noted to the extent of improper operation of the carburetor, the worn parts should be replaced.
4. Inspect floats for bad dents and/or possible leaks.
5. Inspect pump plunger leather for cracks or creases.
6. If choke piston sticks in cylinder, remove welch plug in bottom of housing for inspection of cylinder and air slots. If carbon or dirt is present in slots, clean slots and carefully install new welch plug. Be certain welch plug is installed air tight. NOTE: Thorough cleaning of the slots in the choke piston housing should only be done if it is found that the choke piston does not work free in its cylinder.

Throttle Flange

1. Install primary and secondary throttle shafts.
2. Install throttle valves with trade mark (C in circle) toward idle ports when viewing flange from manifold side.
3. Install idle adjusting needles and springs finger tight, then back out the needles 1 turn each. CAUTION. Do not tighten idle needle screws more than finger tight.
4. Install secondary throttle return spring and secondary throttle lever.
5. Wind spring 1 1/2 turns with tag wire.
6. Install primary shaft thrust washer, inner throttle shaft arm and throttle shaft dog. Hook throttle flex spring on outer throttle lever and throttle shaft dog and install outer lever on primary shaft. Install washer and screw.
7. Using a flat washer on each side of the levers, install connector rod.
8. Install fast idle cam assembly, consisting of secondary lockout lever, spring, lower choke lever, fast idle cam and screw. Be certain the tang on choke lever is inserted under spring on fast idle cam. Cam and levers must operate freely.
9. Install idle speed screw and spring.
10. Place new gasket on carburetor body being sure slot in gasket is lined up with vacumeter passage .
11. Install throttle flange on carburetor body with 6 attaching screws and lock washers.

1. Install primary metering rod jets. NOTE: The primary metering rod jets hove the large holes and must be installed in the primary side of the carburetor. This is the pump cylinder side of the carburetor body.
2. Install secondary main jets.
3. Install 2 low speed jets on primary side of body.
4. Install steel pump inlet ball check and retainer.
5. Install pump passage screw plug.
6. Install brass pump discharge check needle. Be sure needle is installed point down.
7. Install pump discharge cluster gasket, cluster assembly and attaching screw.
8. Install vacumeter spring in vacumeter bore. NOTE: The vacumeter spring affects both economy and performance. If vacumeter piston spring appears to be damaged or distorted, it should be replaced. If any doubt exists, use a new spring for comparison.
9. Install lower pump spring in pump cylinder.

1. Install primary float needle and seat with new gasket.IMPORTANT: Float needles and seats are factory matched and must never be mixed.
2. Install secondary float needle and seat with new gasket.
3. Temporarily install both the primary and secondary float assemblies. NOTE: Float adjustments must be measured with gasket removed.
4. Three separate float adjustments must be made-lateral, vertical, and float drop.
   • Lateral adjustment: Place float gauge under center of float with notched portion of gauge fitted over edge of casting. Sides of float should just clear the vertical uprights of float gauge. Adjustment should be made by bending arms of float.
   • Vertical adjustment: With float gauge in position, floats should just clear the horizontal portion of gauge. Vertical distance between top of float and machined surface of casting must be 1/8" (gauge J-5457) for primary floats and 1/4" (gauge J-5228) for secondary floats. Adjust by bending float arms.
   • Float drop adjustment: With bowl cover held in upright position and measuring from center of float, the distance between top of floats and bowl cover should be 5/8" for primary and 3/4" for secondary floats. Adjust by bending stop tabs on float brackets.
5. Remove floats and intake needles and install new bowl cover gasket.
6. Install vacumeter link and vacumeter piston with lip on link toward bowl cover.
7. Insert pump shaft through bowl cover and retain in position with link and pump arm assembly.
8. Reinstall the primary and secondary float assemblies and needles. CAUTION: Be certain the float and needle assemblies are assembled to match the correct needle seat.
9. Carefully position the bowl cover assembly on the carburetor body being sure the vacumeter piston and pump plunger are aligned so they enter their respective bores.
10. Install 16 bowl cover attaching screws. Determine proper location of different length screws.
11. Tighten all screws evenly and securely in alternate order.
12. Install both metering rods as follows:
    • Install metering rod discs over holes for metering rods in bowl cover.
    • Catch metering rod spring loop with lower end of rod before rod is inserted through metering rod discs, then twist "eye" of rod onto vacumeter piston link assembly.
13. Place metering rod arm in place.
14. Install pump countershaft by sliding shaft through pump operating arm and metering rod arm.
15. Tighten pump arm screw and install atmospheric vent arm.
16. Place washer on lower end of throttle connector rod, install rod into throttle lever while holding lever in wide open position, and retain with spring and retainer.
17. Install throttle connector rod in pump countershaft lever.
18. Install choke piston housing and new gasket.
19. Install choke shaft and piston assembly through bowl cover while guiding piston into cylinder.
20. Place choke valve in position on choke shaft with the "C" (in circle) on valve visible from the top of carburetor. Center choke valve and install screws. Use new screws. IMPORTANT: Make sure that neither valve nor shaft binds in any position and that valve drops free by its own weight.
21. Position baffle plate into choke housing.
22. Install choke coil housing and new gasket on housing with index mark on plastic housing at the bottom. Revolve coil housing in direction opposite to arrow until index mark on coil housing is aligned with index mark on piston housing, and retain with 3 screws and retainers.
23. Install choke operating lever on shaft and tighten screw only enough to permit lever to be moved.
24. Install strainer plug, gasket, and strainer in primary side and install strainer plug and gasket in secondary side. Make carburetor adjustments as outlined in this section under "Care, Maintenance, and Adjustments," before installing the carburetor on the vehicle. NOTE: It is good shop practice to fill the carburetor bowl before installing the carburetor. This reduces the strain on the starting motor and battery and reduces the possibility of back firing while attempting to start the engine. A fuel pump clamped on the bench, a small supply of fuel and the necessary fittings enable the carburetor to be filled and the operation of the float and intake needle and seat to be checked. Operate the throttle several times and check the discharge from the pump jets before installing the carburetor.

General Description

The fuel pumps used on both six and eight cylinder models are of the diaphragm type. The pumps are of similar construction, and the service procedures are the same for each. Both pumps are located on lower right front corner on each engine. On the six cylinder models, an eccentric on the camshaft actuates the pump rocker arm. The eight cylinder pump rocker arm is actuated by a push rod, located in the cylinder block between the pump and the fuel pump eccentric on the camshaft. The eight cylinder model pump is inverted relative to the six cylinder model pump, and has a larger capacity. A leather oil seal is used on the six and a rubber oil seal on the eight. Figure 35 and figure 36 show a cross-section of each pump.

The fuel pump consists of a body, rocker arm and link assembly, fuel diaphragm, fuel diaphragm spring oil seal, seal spring, cover, inlet and outlet valves pulsator diaphragm and cover. The fuel diaphragm consists of several layers of specially treated cloth, which are not affected by gasoline, held together by two metal discs and a push rod. An oil seal assembly fits around the push rod and is held down on the pump body by the seal spring.

As the rocker arm is moved toward the pump, compressing the rocker arm spring, it bears against the fuel link which is pivoted on the rocker arm pin bushing. The end of the fuel link

is hooked to the fuel diaphragm pull rod. This moves the diaphragm away from fuel chamber and the fuel diaphragm spring is compressed. The enlarging fuel chamber moves gasoline from the tank through the fuel line, inlet valve and into the space on the valve side of the diaphragm.

As the rotating eccentric permits the rocker arm to move away from contact with the link, the compressed diaphragm spring is free to move the diaphragm up to expel the fuel through the outlet valve to the carburetor bowl and float needle valve.

Because the fuel diaphragm is moved toward the valves only by the fuel diaphragm spring, the pump delivers fuel to the carburetor only when the pressure in the outlet line is less than the pressure maintained by the diaphragm spring. Thus, fuel is delivered to the carburetor only when the needle valve is open. When the needle valve is closed by pressure of fuel on the float in the carburetor, the pump builds up pressure until the diaphragm spring is compressed. The diaphragm remains in a stationary condition to maintain a static pressure until more fuel is required. Normal diaphragm stroke is about 1/64" .The pulsator diaphragm in the fuel section cover acts as a pulsator or air dome to increase effective fuel flow by leveling off the flow variation experienced with the two stroke diaphragm cycle.

Care, Maintenance and Adjustments

The fuel pump should be checked regularly to make sure that the mounting bolts, cover to body bolts, pulsator diaphragm cover screw and inlet and outlet connections are tight.

FUEL PUMP INSPECTION AND TEST

Check the pump while it is mounted on the engine.

1. Be sure there is gasoline in the tank.
2. Note that the line from the tank to the pump is the suction side of the system and that the line from the pump to the carburetor is the pressure side of the system. Thus, a leak is apparent on the pressure side by dripping fuel, but a leak on the suction side will not be apparent except in its effect of reducing volume of fuel on the pressure side.
3. Tighten any loose line connections and look for bends or kinks in lines which would reduce fuel flow.
4. Tighten diaphragm flange screws.
5. Disconnect fuel pipe at carburetor. Place suitable container of one pint minimum capacity at end of pipe. Start engine and run at 1000 RPM. Pump should deliver one pint of fuel within 45 seconds. If no gasoline, or only a little flows from open end of pipe then the fuel pipe is clogged or the pump is inoperative. Before removing pump, remove gas tank cap, disconnect both inlet and outlet pipes and blow through them with an air hose to make sure they are clear. This will eliminate the possibility of a clogged gas strainer in the fuel tank. Reconnect pipes to pump and retest flow.
6. Even if fuel flows in good volume, from pipe at carburetor, it is advisable to make a test of fuel delivery pressure to be certain that pump is operating within specified limits.
7. Attach a low reading pressure gauge to disconnect end of pump to carburetor pipe. Run engine at approximately 450 and 1000 R.P.M. on gasoline in carburetor bowl and note reading on pressure gauge.
8. If pump is operating properly the pressure will be 3 1/2 to 4 1/2 psi on six cylinder models, and 4 to 5 1/4 psi on eight cylinder models, and will remain constant at speeds between 450 and 1000 R.P.M. If pressure is too low or too high, or varies materially at different speeds, the pump should be removed for repair or replacement.

REMOVAL

1. Disconnect fuel inlet and outlet pipes at fuel pump fuel cover.
2. Remove two fuel pump mounting bolts and lockwashers and remove pump and gasket.
3. On eight cylinder models, if rocker arm push rod is to be removed, remove two adapter mounting bolts and lockwashers and remove adapter and gasket from block. Remove push rod from block.

After removal of pump from engine and before disassembly is started, plug all openings and thoroughly wash exterior of pump with cleaning solvent to remove all dirt and grease.

DISASSEMBLY

1. Remove fuel pulsator diaphragm plate and diaphragm from fuel cover.
2. Mark edges of fuel cover and body flange with file. The parts may then be assembled in the same relative position.
3. Remove cover screws and lock washers. Separate fuel cover from body by jarring cover loose with a light plastic hammer.
4. On eight cylinder models, unhook the fuel diaphragm from the fuel link by compressing spring slightly and moving entire diaphragm assembly away from rocker arm to slide the eye of the pull rod off the hook of the lever. Lift the diaphragm spring, and lower spring seat out of the body.
5. On six cylinder models, raise fuel pump link with a screwdriver (fig. 37). Unhook diaphragm from the link by pressing down and away from the rocker arm side. Remove oil seal and retainer from diaphragm.

1. Clean and rinse all metal parts in solvent. Blow out all passages with air hose. Figure 38 shows the six cylinder model disassembled.
2. Inspect pump body and fuel cover for cracks, breakage and distorted flanges. Examine all screw holes for stripped or crossed threads. Replacement of pump assembly is advisable if one of the main castings is not serviceable.
3. On eight cylinder models, inspect the diaphragm pull rod oil seal in pump body. If damaged or of doubtful condition, clear the staked metal with a sharp chisel, file or suitable scraper and pry out the metal retainer and discard the rubber seal.
4. Inspect the rocker arm and link for excessive wear and for loose hinge pin.
5. Replace diaphragm.
6. Check the condition of the valves by pushing each valve off its seat with a thin rod or pencil. A hooked wire may be inserted through inlet opening in fuel cover to move the fuel inlet valve off its seat. If a valve sticks to its seat, if it moves off its seat and does not rebound, or if the cage is damaged, the complete valve must be replaced. To remove the valves, clear the staked metal with a sharp chisel, file or suitable scraper and pull valve out with a hook shaped tool.
7. Replace rocker arm spring and diaphragm springs as removed, because old springs may be distorted, weak or corroded.

1. On six cylinder models, install the oil seal to the diaphragm push rod in the following manner. Assemble oil seal spring, upper retainer, two leather seals and lower retainer with convex side out. This is extremely important in order to seal the fuel pump from any oil that might come up from the crankcase. Raise the fuel pump link with a screwdriver (fig. 38), install the diaphragm spring and hook the diaphragm pull rod over the end of the link.
2. On eight cylinder models, if push rod seal was removed, assemble new seal in retainer so seal fits inside retainer, and start assembly straight in bore in body with retainer facing out. Press retainer down firmly with flat end of 7/8 inch diameter bar. Retain by staking die cast lip in four places.
3. On eight cylinder models, set the diaphragm spring on the staked-in seal and the retainer on top of the spring. Push diaphragm pull rod through retainer, spring and oil seal. Flat of pull rod must be at right angles to fuel link. Compress diaphragm spring slightly, invert pump body and hook diaphragm pull rod to fuel link.
4. If either valve was removed from the fuel cover, install by placing gasket in recess and pressing valve into place. Outlet valve cage must face bottom of cover, and inlet valve cage must face opposite. Secure valve assembly by staking cover metal in four places around valve
5. Place new pulsator diaphragm over fuel cover opening, install plate and retain with the screw and fiber washer.
6. Install cover on body, making sure that file marks on cover and body line up. Push on rocker arm until diaphragm is flat across body flange. Install cover screws and lock washers loosely until screws just engage lockwashers. Push rocker arm through its full stroke to flex diaphragm and hold in that position while tightening cover screws securely.Caution: Diaphragm must be flexed to its full stroke while tightening cover screws or pump will deliver too much pressure.

Installation

1. On eight cylinder models, if rocker arm push rod was removed, place heavy grease on one end of push rod and insert that end into opening in block. Slide push rod up against camshaft. Install adapter gasket and adapter, securing with two bolts and lockwasher.
2. Install fuel pump gasket and fuel pump.
3. Connect fuel pipes to pump.

General Description

Air cleaners on all models operate primarily to remove dust and dirt from the air that is take into the carburetor and engine. All air cleaner used incorporate flame arresters. In addition, the air cleaner design is such that the sound of a rushing into the carburetor is deadened, reducing engine operating noise.

Standard Cleaner

The standard cleaner has an element consisting of a metallic gauze filter that is saturated heavy oil. As air filters through this element, dirt and dust are deposited on the oily surfaces o the gauze. This gauze also quenches any flame that may be caused by engine backfire through the carburetor.

Oil Bath Air Cleaner

A heavy duty, oil bath type cleaner is also available when vehicles are to be used in unusually dusty areas. This cleaner is interchangeable with the standard air cleaner and will not affect power or economy in any way. Air entering this cleaner must go directly down in a narrow space around the cleaner to the oil level in the cleaner body. The air must then turn and go up through the copper gauze and into the carburetor. As the direction of air flow is reversed, heavy particles in the air are thrown into the oil in the cleaner body, greatly reducing the amount of dirt to be deposited in the copper gauze. Oil is carried up into the gauze with the air. It is caught on the gauze, where it aids in trapping the finer dust particles from the air. The predetermined amount of oil being carried into the gauze washes the gauze and carries the dirt back to the sump. (fig. 39).

Service Operations

STANDARD CLEANER

1. Remove cover wing nut, cover and filter element.
2. Wash filter element thoroughly in cleaning solvent.
3. Let element dry and dip in engine oil. Drain surplus oil from element.
4. Install element and cover, and secure with wing nut.

OIL BATH AIR CLEANER

1. Loosen clamp and mounting screws and remove cleaner assembly.
2. Remove cover wing nut, cover and filter element assembly.
3. Empty oil out of cleaner and clean out o and accumulated dirt.
4. Wash body with cleaning solvent and wipe dry.
5. Wash filter element by slushing up and do in cleaning solvent.
6. Dry filter unit with an air hose or let stand until dry.
7. Fill body of cleaner with one pint of SAE 50 engine oil. If expected temperatures are to be consistently below freezing, use SAE 20 engine oil.
8. Assemble filter and cover assembly to body of cleaner.
9. Install cover wing nut.
10. Install cleaner, making sure it fits tight and is set down securely. Tighten clamp and mounting screws.

FUEL SYSTEM

Symptom and Probable Cause
Probable Remedy

Excessive Fuel Consumption

a. Improper adjustment
a. Adjust idling mixture screws

b. Improper float adjustment
b. Check and adjust float level

c. Dirty air cleaner
c. Clean air cleaner

d. Fuel leaks
d. Check carburetor, fuel pump, fuel tank and connections for leaks

e. Sticking controls
e. Check choke and throttle valve and manifold heat control valve or spring for proper operation

f. Improper engine temperature
f. Refer to Cooling Section

g. Dragging brakes
g. Refer to Brake Section

h. Engine improperly tuned
h. Tune engine-See Engine Section

i. Tires underinflated
i. Inflate to recommended pressure

j. Dirt in carburetor
j. Clean carburetor

k. Wrong jets
k. Install correct jets

Fast Idling

a. Improper adjustment
a. Adjust idling and throttle stop screws

b. Controls Sticking
b. Free up controls and lubricate linkage

c. Automatic choke sticking
c. Clean automatic choke

d. Poor automatic choke heat connection
d. Repair automatic choke heat connections

Engine Dies (Will Not Idle)

a. Idle speed or mixture screws improperly adjusted.
a. Adjust carburetor

b. Low speed jet or idle passages plugged.
b. Disassemble and clean carburetor

c. Vacuum leaks, carburetor or manifold
c. Replace necessary gaskets

d. Float needle and seat loose, worn or sticking
d. Replace needle and seat

Engine Misses on Acceleration

a. Accelerating pump jet plugged
a. Disassemble and clean carburetor

b. Accelerating pump check valves sticking or leaking
b. Disassemble and clean carburetor

c. Faulty power piston
c. Free-up or replace power piston

d. Worn pump leather
d. Replace pump plunger

e. Improper spark plug adjustment
e. Adjust spark plugs-See Engine Section

f. Improper tappet adjustment
f. Adjust tappets-See Engine Section

g. Sticking or burned valves
g. Free up sticking valves or replace burned

Fuel System Specifications

Air Cleaner

Make - AC
Type:
Standard - Mesh
Optional - Oil Bath

Carburetor

Make and Type:
6-cylinder - GM Model "BC"" Downdraft with Automatic Choke
8-cylinder - GM Model 2GC Downdraft, 2 barrel with Automatic Choke
8-cylinder (opt.) - Carter WCFB Downdraft, 4 barrel with Automatic Choke

Fuel Pump, 6-cylinder

Make, Model - AC, model EM
Pressure - 3 1/2 to 4 1/2 psi

Fuel Pump, 8-cylinder

Make, Model - AC, model EM
Pressure - 4 to 5 1/4 psi