GM Corvette 1963-1982 Repair Guide

Carter AFB Carburetor


See Figure 1

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Fig. Fig. 1: Carter AFB bowl cover parts

The Carter AFB (aluminum four-barrel) carburetor is a high performance option found on the 327 cubic inch Corvette engine from 1963-65. It is a four-throat downdraft type and offers improved flow rates over the standard carburetor. A clean air system reduces contamination of the choke vacuum circuit and linkage, and subsequent malfunctioning.


Idle Speed and Mixture

Idle speed and mixture are adjusted with the engine thoroughly warmed and idling and with the aid of a tachometer and vacuum gauge attached to the engine. With the choke fully off, adjust the idle-speed adjustment screw to give 475 rpm (450 for automatic transmission models in Drive). Adjust each idle-mixture screw until peak steady vacuum is achieved at the specified rpm.

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 Powerglide models and one notch lean with synchromesh.

Float See Figure 2

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Fig. Fig. 2: Carter AFB float drop adjustment

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 to adjust. The 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 in. Bend to adjust.

The float drop is adjusted by holding the air horn in the 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 in.

Intermediate Choke Rod

The intermediate choke rod adjustment begins with the removal of the choke coil housing assembly, gasket and baffle plate. Position a 0.026 in. wire gauge between the bottom of the slot in the piston and the top of the slot in the choke piston housing. Close the choke piston against the gauge and secure it with a rubber band. Now 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 in.

Accelerator Pump

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

Unloader, Closing Shoe, and Secondary Throttle

To adjust the unloader, hold the throttle wide open and bend the unloader tang to obtain a 3 / 16 in. clearance between the upper edge of the choke valve and inner wall of the air horn.

Clearance between the positive closing shoes on the primary and secondary throttle valves is checked with the valves closed. Bend the secondary closing as required to obtain a clearance of 0.20 in.

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.


See Figure 3

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Fig. Fig. 3: Carter AFB main body components

  1. Remove the pump rod and intermediate choke rod. Remove the outer lever and washer from the choke shaft, then remove the inner lever and fast-idle rod as an assembly. Remove the step-up position cover plates, piston, and step-up rod and spring. Lightly tap the fuel inlet fitting. Before removing it, remove its gasket and strainer then carefully lift the top cover to protect the floats and pump plunger from damage.
  3. Remove the float lever pins, floats, float needles, seats, and gaskets. Keep separate to avoid unnecessary adjustment. Remove the pump plunger lever, S link, plunger, and cover gasket.
  5. Do not remove the choke valve and shaft(s) unless there is obvious shaft binding or damage to the valve.
  7. Remove the accelerator-pump lower spring and, after checking the fuel for contamination, drain the bowl. Sweep a magnet around the bottom of the bowl while fuel is still present to capture iron oxide dust or metal particles which may damage the needle seats. Water contamination will appear as milky globules at the bottom of the fuel bowl.
  9. Remove the choke housing cover, gasket, and baffle. Remove the O-ring seal from the vacuum opening in the mounting boss. Remove the choke piston, levers, pump cluster and gasket, and pump discharge needle. Remove the venturi cluster. The venturi assemblies are dissimilar and cannot be assembled in the wrong location. Primary venturi gaskets differ from secondary.
  11. Remove the secondary auxiliary valves, idle-mixture screws and springs, and all four metering jets. Metering rods are used in the primary metering jets and these jets are visibly larger than their secondary counterparts. Remove the pump intake check valve and seat assembly.
  13. Wash all parts except the choke coil housing and the pump plunger in carburetor cleaning solution. Clean the choke housing in gasoline.
  15. Reassembly is the reversal of this procedure.