Chevrolet Full-size Cars 1968-1978 Repair Guide

Carter AFB 4-BBL Carburetor



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Fig. Fig. 1 Top view of various Carter AFB components

Automatic Choke

The automatic choke is correctly adjusted when the scribe mark on the coil housing is aligned with the center notch in the choke housing for automatic transmission vehicles and one notch lean for manual transmission vehicles.


Remove the metering rods and the bowl cover. Align the float by sighting down its side to determine if it is parallel with the outer edge of the air horn. Bend the float to adjust. Float level is adjusted with the air horn inverted and the air horn gasket in place. Clearance between each float (at the outer end) and the air horn gasket should be 5 / 16 ". Bend to adjust.

Float Drop

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Fig. Fig. 2 Float drop measuring points for the Carter AFB carburetor

Float drop is adjusted by holding the air horn in an upright position and bending the float arm until the vertical distance from the air horn gasket to the outer end of each float measures 3 / 4 ".

Intermediate Choke Rod

Remove the choke coil housing assembly, gasket, and baffle plate. Position a 0.026" wire gauge between the bottom of the slot in the piston and the top of the float in the choke piston housing. Close the choke piston against the gauge and secure it with a rubber band. Bend the intermediate choke rod so that the distance between the top edge of the choke valve and the air horn divider measures 0.070".

Accelerator Pump

The first step in adjusting the accelerator pump is to push aside the fast idle cam and firmly seat the throttle valves. Bend the pump rod at the lower angle to obtain a 1 / 2 " clearance between the air horn and the top of the plunger shaft.

Unloaded, Closing Shoe, and Secondary Throttle

To adjust the unloader, hold the throttle wide open and bend the unloaded tang to obtain a u-/ 16 " clearance between the upper edge of the choke valve and the inner wall of the air horn.

The clearance between the positive closing shoes on the primary and secondary throttle valves is checked with the valves closed. Bend the secondary closing shoe as required to obtain a clearance of 0.020".

The secondary throttle opening is governed by the pick-up lever on the primary throttle shaft. It has two points of contact with the loose lever on the primary shaft. If the contact points do not simultaneously engage, bend the pick-up lever to obtain proper engagement. The primary and secondary throttle valve opening must be synchronized.