REMOVAL & INSTALLATION
See Figure 1
- Remove the air cleaner.
- Disconnect the fuel and vacuum lines. It might be a good idea to tag them to avoid confusion upon assembly.
- Disconnect the choke rod.
- Disconnect the accelerator linkage.
- Disconnect the automatic transmission linkage.
- Unbolt and remove the carburetor.
- Remove the base gasket.
- Before installation, make sure that the carburetor and manifold sealing surfaces are clean.
- Install a new carburetor base gasket.
- Install the carburetor, then position the fuel and vacuum lines.
- Bolt down the carburetor evenly, tightening the bolts in a crisscross pattern to 7 ft. lbs. (9 Nm), then to 14 ft. lbs. (19 Nm).
- Secure the fuel and vacuum lines.
- Connect the accelerator and automatic transmission linkage. If the transmission linkage was disturbed, it will have to be adjusted.
- Connect the choke rod.
- Install the air cleaner. Adjust the idle speed and mixture.
Efficient carburetion depends greatly on careful cleaning and inspection during overhaul, since dirt, gum, water, or varnish in or on the carburetor parts is often responsible for poor performance.
Overhaul your carburetor in a clean, dust-free area. Carefully disassemble the carburetor, referring often to the exploded views. Keep all similar and look-alike parts segregated during disassembly and cleaning to avoid accidental interchange during assembly. Make a note of all jet sizes.
When the carburetor is disassembled, wash all parts (except diaphragms, electric choke units, pump plunger, and any other plastic, leather, fiber or rubber parts) in clean carburetor solvent. Do not leave parts in the solvent any longer than is necessary to sufficiently loosen the deposits. Excessive cleaning may remove the special finish from the float bowl and choke valve bodies, leaving these parts unfit for service. Rinse all parts in clean solvent and blow them dry with compressed air or allow them to air dry. Wipe clean all cork, plastic, leather and fiber parts with a clean, lint-free cloth.
Blow out all passages and jets with compressed air and be sure that there are no restrictions or blockages. Never use wire or similar tools to clean jets, fuel passages, or air bleeds. Clean all jets and valves separately to avoid accidental interchange.
Check all parts for wear or damage. If wear or damage is found, replace the defective parts. Especially check the following:
- Check the float needle and seat for wear. If wear is found, replace the complete assembly.
- Check the float hinge pin for wear and the float(s) for dents or distortion. Replace the float if fuel has leaked into it.
- Check the throttle and choke shaft bores for wear or an out-of-round condition. Damage or wear to the throttle arm, shaft, or shaft bore will often require replacement of the throttle body. These parts require a close tolerance of fit. Wear may allow air leakage, which could affect starting and idling.
Throttle shafts and bushings are not included in overhaul kits. They can be purchased separately.
- Inspect the idle mixture adjusting needles for burrs or grooves. Any such condition requires replacement of the needle, since you will not be able to obtain a satisfactory idle.
- Test the accelerator pump check valves. They should pass air one way but not the other. Test for proper seating by blowing and sucking on the valve. Replace the valve if necessary. If the valve is satisfactory, wash the valve again to remove breath moisture.
- Check the bowl cover for warped surfaces with a straightedge.
- Closely inspect the valves and seats for wear and damage, replacing as necessary.
- After the carburetor is assembled, check the choke valve for freedom of operation.
Carburetor overhaul kits are recommended for each overhaul. These kits contain all gaskets and new parts to replace those that deteriorate most rapidly. Failure to replace all parts supplied with the kit (especially gaskets) can result in poor performance later.
Carburetor manufacturers supply overhaul kits of three basic types: minor repair, major repair, and gasket kits. Basically, they contain the following:Minor Repair Kits
Major Repair Kits
After cleaning and checking all components, reassemble the carburetor, using new parts and referring to the exploded view. When reassembling, make sure that all screws and jets are tight in their seats, but do not overtighten, as the tips will be distorted. Tighten all screws gradually, in rotation. Do not tighten needle valves into their seats; uneven jetting will result. Always use new gaskets. Be sure to adjust the float level when reassembling.Carter Model BBD
See Figure 2
- Place the carburetor on a repair stand to protect throttle valves from damage and to provide a stable base for working.
- Unfasten the retaining clip from the accelerator pump arm link and disconnect the line. Remove the stepper motor.
- Remove the step-up piston cover plate and gasket from atop the air horn.
- Remove the screws and locks from the accelerator pump arm and the vacuum piston rod lifter. Then, slide the pump lever out to the air horn. The vacuum piston and step-up rods can now be lifted straight up and out of the air horn as an assembly.
- Remove the vacuum hose from between the carburetor main body and the choke vacuum diaphragm at the main body tap.
- Remove the choke diaphragm, linkage and bracket assembly and place to one side to be cleaned as a separate item.
- Remove the retaining clip from the fast idle cam link and remove the link from the choke shaft lever.
- Remove the fast idle cam retaining screw and remove the fast idle cam and linkage.
- Remove the air horn retaining screws and lift the air horn straight up and away from the main body. Discard the gasket.
- Invert the air horn and compress the accelerator pump drive spring and remove the "S'' link from the pump shaft. The pump assembly can now be removed.
- Remove the fuel inlet needle valve, seat and gasket from the main body.
- Lift out the float fulcrum pin retainer and baffle. Then lift out the floats and fulcrum pin.
- Remove the main metering jets.
- Remove the venturi cluster screws, then lift the venturi cluster and gaskets up and away from the main body. Discard the gaskets. Do not remove the idle orifice tubes or the main vent tubes from the cluster. They can be cleaned in a solvent and dried with compressed air.
- Invert the carburetor and drop out the accelerator pump discharge and intake check balls.
- Remove the idle mixture screws from the throttle body, after lightly bottoming and noting the number of turns. Record the turns in for reference when installing the mixture screws.
- Remove the screws that attach the throttle body to the main body. Separate the bodies.
- Test the freeness of the choke mechanism in the air horn. The choke shaft must float free to operate correctly. If choke shaft sticks, or appears to be gummed from deposits in the air horn, a thorough cleaning will be required.
- The carburetor now has been disassembled into three main units: the air horn, main body, and throttle body. Components are disassembled as far as necessary for cleaning and inspection.
Check the throttle shaft for excessive wear in the throttle body. If wear is extreme, it is recommended that the throttle body assembly be replaced rather than installing a new shaft in the old body. Install the idle mixture screws in the body. The tapered portion must be straight and smooth. If the tapered portion is grooved or ridged, a new idle mixture screw should be installed to insure having correct idle mixture control.MAIN BODY
- Invert the main body and place insulator in position, then place the throttle body on the main body and align. Install the screws and tighten securely.
- Install the accelerator pump discharge the check ball ( 5 / 32 inch diameter) in the discharge passage. Drop the accelerator pump intake check ball ( 3 / 16 inch diameter) into the bottom of the pump cylinder.
- To check the accelerator pump system, fuel inlet and discharge the check balls, and proceed as follows:
- Pour clean gasoline into the carburetor bowl, approximately 1 / 2 inch deep. Remove the pump plunger from the container of mineral spirits and slide down into the pump cylinder. Raise the plunger and press lightly on the plunger shaft to expel the air from the pump passage.
- Using a small clean brass rod, hold the discharge check ball down firmly on its seat. Again raise the plunger and press downward. No fuel should be emitted from either the intake or discharge passage. If any fuel does emit from either passage, it indicates the presence of dirt or a damaged check ball or seat. Clean the passage again and repeat the test. If leakage is still evident, stake the check ball seats (place a piece of drill rod on top of check ball and lightly tap drill rod with a hammer to form a new seat), remove and discard the old balls, and install new check balls. The fuel inlet check ball is located at bottom of the plunger well. Remove fuel from bowl.
- Install the discharge check ball. Install new gaskets on the venturi cluster, then position it in the main body. Install the cluster screws and tighten securely.
- Install the main metering jets.
The carburetors are equipped with a synthetic rubber tipped fuel inlet needle. The viton needle tip is not affected by gasoline and is stable over a wide range of temperatures. The tip is flexible enough to make a good seal on the needle seat, and to give increased resistance to flooding.
The use of the synthetic rubber tipped inlet needle requires that care be used in adjusting the float setting. Care should be taken to ensure this accurately in order to secure the best performance and fuel economy.
When replacing the needle and seat assembly (inlet fitting), the float level must also be checked, as dimensional difference between the old and new assemblies may change the float level. Refer to the carburetor adjustments information for this procedure.
- Install the floats and fulcrum pin.
- Install the fulcrum pin retainer and baffle.
- Install the fuel inlet needle valve, seat and gasket in the main body.
- Place the accelerator pump drive spring on the pump plunger shaft then insert the shaft into air horn. Compress the spring far enough to insert the "S'' link.
- Install the pump lever, vacuum piston rod lifter and accelerator pump arm in the air horn.
- Drop the intake check ball into the pump bore. Install the baffle into the main body. Place the step-up piston spring in the piston vacuum bore. Position a new gasket on the main body and install the air horn.
- Install the air horn retaining screws and tighten alternately, a little at a time, to compress the gasket securely.
- To qualify the step-up piston, adjust the gap by turning the Allen head calibration screws on top of the piston. See the adjustment portion of this section for proper measurement. Record the number of turns and direction to obtain this dimension for this must be reset to its original position after the the vacuum step-up piston adjustment has been made.
- Carefully position the vacuum piston metering rod assembly into the bore in air horn making sure metering rods are in the main metering jets. Then place the two lifting tangs of the plastic rod lifter under the piston yoke. Slide the shaft of the accelerator pump lever through the rod lifter and pump arm. Install the two locks and adjusting screws, but do not tighten until after the adjustment is made.
- Install the fast idle cam and linkage. Tighten the retaining screw securely.
- Connect the accelerator pump linkage to the pump lever and throttle lever. Install the retaining clip.
Inspect the diaphragm vacuum fitting to insure that the passage is not plugged with foreign material. Leak check the diaphragm to determine if it has internal leaks. To do this, first depress the diaphragm stem, then place a finger over the vacuum fitting to seal the opening. Release the diaphragm stem. If the stem moves more than 1 / 16 inch (2mm) in 10 seconds, the leakage is excessive and the assembly must be replaced.
Install the diaphragm assembly on the air horn as follows:
- Engage the choke link in the slot in the choke lever.
- Install the diaphragm assembly, secure with the attaching screws.
- Inspect the rubber hose for cracks before placing it on the correct carburetor fitting. Do not connect the vacuum hose to the diaphragm fitting until after the vacuum kick adjustment has been made.
- Loosen the choke valve attaching screws slightly. Hold the valve closed, with fingers pressing on high side of the valve. Tap the valve lightly with a screwdriver to seat in the air horn. Tighten the attaching screws securely and stake by squeezing with pliers.
The choke diaphragm adjustment controls the fuel delivery while the engine is running. It positions the choke valve within the air horn by action of the linkage between the choke shaft and the diaphragm. The diaphragm must be energized to measure the vacuum kick adjustment. Vacuum can be supplied by an auxiliary vacuum source.
Float and Fuel Level
See Figure 3
- Remove the air horn.
- Apply light finger pressure to the vertical float tab to exert GENTLE pressure against the inlet needle.
- Lay a straight edge across the float bowl and measure the gap between the straight edge and the top of the float at its highest point. The gap should be 1 / 4 in. (6mm).
- To adjust, remove the float and bend the lower tab. Replace the float and check the gap.
Fast Idle Linkage
See Figure 4
This adjustment is performed with the air cleaner removed.
- Loosen the choke housing cover and rotate it 1 / 4 turn to the right. Tighten one screw.
- Slightly open the throttle and place the fast idle screw on the second cam step.
- Measure the distance between the choke plate and the air horn wall. The distance should be 0.095 in. (2.4mm).
- If adjustment is necessary, bend the fast idle cam link down to increase or up to decrease the gap.
- Return the choke cover cap to the original setting.
Initial Choke Valve Clearance
See Figure 5
- Position the fast idle screw on the top step of the fast idle cam.
- Using a vacuum pump, seat the choke vacuum break.
- Apply light closing pressure on the choke plate to position the plate as far closed as possible without forcing it.
- Measure the distance between the air horn wall and the choke plate. If it is not 9 / 64 in. (3.6mm), bend the choke vacuum break to adjust the clearance.
The automatic choke setting is made by loosening the choke cover in the desired direction as indicated by an arrow on the face of the cover. the original setting will be satisfactory for most driving conditions. However, if the engine stumbles or stalls on acceleration during warm-up, the choke may be set richer or leaner no more than two graduations from the original setting.Choke Unloader
See Figure 6
With the throttle held fully open, apply pressure on the choke valve toward the closed position and measure the clearance between the lower edge of the choke valve and the air horn wall. The measurement should be 9 / 32 in. (7mm). Adjust by bending the tang on the throttle lever which contacts the fast idle cam. Bend toward the cam to increase the clearance.
Do not bend the unloader down from a horizontal plane. After making the adjustment, make sure the unloader tang does not contact the main body flange when the throttle is fully open. A clearance of 0.070 in. (1.8mm) must be present. Final unloader adjustment must always be done on the vehicle. The throttle should be fully opened by depressing the accelerator pedal to the floor. This is to assure that full throttle is obtained.
Vacuum (Step-up) Piston Gap
See Figure 7
- Turn the adjusting screw (mounted on top of the unit), so that the gap between the metering rod lifter's lower edge and the top of the vacuum piston is 1 / 32 in. (0.03mm).
- Counting the number of turns involved, turn the curb idle adjustment screw counterclockwise, until the throttle valves are completely closed.
- Fully depress the vacuum piston, while exerting moderate pressure on the metering rod lifter tab. In this position, tighten the rod lifter lock screw.
- Release the piston and rod lifter.
The accelerator pump should now be adjusted.
- Return the curb idle adjustment screw to its original position.
See Figure 8
- Counting the number of turns involved, turn the curb idle adjustment screw counterclockwise, until the throttle valves are completely closed.
- Open the choke valve so that the fast idle cam will allow the throttle valves to seat in their bores.
- Turn the curb idle adjustment screw clockwise, so that it just barely touches the stop, then turn it 2 additional full turns.
- Measure the distance between the surface of the air horn and the top of the accelerator pump shaft with a T-scale. The distance should be 33 / 64 in. (13mm).
- If the dimension is not correct, loosen the pump arm adjusting screw and rotate the sleeve to adjust the pump travel. Tighten the lock screw.
- Return the curb idle screw to its original position.