AMC Coupes/Sedans/Wagons 1975-1988 Repair Information

Carter BBD 2-BBL Carburetor

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See Figures 1 and 2

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Fig. Fig. 1: Exploded view of the Carter BBD carburetor components



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Fig. Fig. 2: Component list for the Carter BBD carburetor

ADJUSTMENT - Float Level



See Figure 3

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Fig. Fig. 3: Carter BBD carburetor float adjustment points

Float Adjustment

  1. Remove the carburetor air horn.
  2.  
  3. Gently hold the lip of the float against its needle to raise the float.
  4.  
  5. Measure float level by placing a straightedge across the float bowl. Float level should be maintained at 0.250 in. (6.35mm), plus or minus 0.032 in. (0.81mm). Release the floats.
  6.  
  7. If necessary, adjust by bending the float lips as required.
  8.  

Do not bend float lip while it is resting against the needle as this may deform the synthetic needle tip and cause a false setting.

  1. Install the air horn.
  2.  

Fast Idle See Figure 4

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Fig. Fig. 4: Adjusting the fast idle cam on the Carter BBD carburetor

Perform this adjustment with the carburetor installed on the engine. If the car is equipped with a Transmission Controlled Spark (TCS) system and/or an Exhaust Gas Recirculation (EGR) system, be sure that both are disconnected before attempting to set fast idle speed.

  1. Start engine and allow it to reach normal operating temperature.
  2.  
  3. Connect a tachometer to the engine.
  4.  
  5. Set the fast idle adjusting screw so that it contacts the second step of the fast idle cam and rests against the shoulder of the high step.
  6.  
  7. Rotate the fast idle adjusting screw until a fast idle speed of 1700 rpm is obtained.
  8.  
  9. Remove the tach and return the engine to normal idle speed after the adjustment is completed.
  10.  

Automatic Choke

This adjustment may be made with the carburetor either on or off the engine.

  1. Loosen the choke cover retaining screws.
  2.  
  3. Rotate the choke cover in the direction of its arrow to the specified setting. Refer to the carburetor specification charts.
  4.  
  5. Tighten the retaining screws.
  6.  
  7. If the car stumbles or stalls at the specified choke setting during engine warm-up, adjust the setting to (richer or leaner) until the car runs properly.
  8.  

Never set the choke more than two notches in either direction of the recommended setting.

Choke Unloader

  1. Hold the throttle in the wide open position and apply pressure on the choke plate toward the closed position.
  2.  
  3. Measure the distance between the lower edge of the choke plate and the air horn wall (see the `Carburetor Specifications' chart).
  4.  
  5. If necessary, adjust by bending the unloader tang where it contacts the fast idle cam. Bend toward the cam to increase clearance, and away from the cam to decrease clearance.
  6.  

Do not bend the unloader tang down from the horizontal plane. After adjusting, make sure that the unloader tang maintains at least a 0.070 in. (1.78mm) clearance from the flange of the main body at wide open throttle position.

  1. Operate the throttle and make sure that the unloader does not bind against the carburetor or linkage. Also make sure the wide open throttle can be reached by fully depressing the gas pedal. If not, remove excess padding from beneath the floor mat or reposition the throttle cable bracket.
  2.  

Initial Choke Valve

  1. Remove the choke cover.
  2.  
  3. Using a vacuum source which holds a minimum of 19 in. Hg, pull the diaphragm in against its stop.
  4.  
  5. Open the throttle valve slightly so that the fast idle screw locates on the high step of the cam.
  6.  
  7. Hold the choke bimetallic coil tang in the closed position and measure the clearance between the choke plate and the air horn wall. The distance should be 0.128 in. (3.25mm), plus or minus 0.010 in. (0.254mm).
  8.  
  9. Adjust as necessary by bending the `S' shaped section of the diaphragm connector link.
  10.  

Vacuum Step-Up Piston Gap See Figure 5

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Fig. Fig. 5: Carter BBD carburetor vacuum piston components

  1. Remove the step-up piston cover plate and gasket from the carburetor air horn.
  2.  
  3. Adjust the gap in the step-up piston to 0.040 in. (1.016mm), plus or minus 0.015 in. (0.38mm) using the allen head screw on top of the piston. Turning the screw clockwise richens the fuel mixture and turning counterclockwise leans it out.
  4.  
  5. Back off the curb idle adjustment until the throttle valves are fully closed, then rotate the idle screw inward one complete turn. Make a note of the number of turns so that the idle screw can be returned to its original position.
  6.  
  7. While keeping moderate pressure on the rod lifter tab, fully depress the step-up piston and tighten the rod lifter lockscrew.
  8.  
  9. Release the piston and rod lifter, and return the curb idle screw to its original position.
  10.  
  11. Install the step-up piston cover plate and gasket.
  12.  

Accelerator Pump See Figure 6

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Fig. Fig. 6: Carter BBD carburetor accelerator pump adjustment

  1. Back off the curb idle screw until the throttle valves (plates) are completely closed. Then, open the choke valve (plate) so that the fast idle cam permits the throttle valves to seat in their bores. Make sure that the accelerator pump `S' link is located in the outer hole of the pump arm.
  2.  
  3. Turn the curb idle screw clockwise until it just contacts its stop, and then continue to rotate two complete turns.
  4.  
  5. Measure the distance between the surface of the air horn and the top of the accelerator pump shaft. This distance should be 0.500 in. (12.7mm).
  6.  
  7. Adjust the pump travel as necessary, by loosening the pump arm adjusting lockscrew and rotating the sleeve until the proper measurement is obtained. Then, tighten the lockscrew.
  8.  

 
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