How to Adjust the Mixture on a Carter AFBby John Stevens J.D.
The Carter AFB four-barrel carburetor has been among the most popular choices among automotive enthusiasts for decades. Known for its chrome finish, the AFB is also known for its user-friendly adjustment points. Among the most common adjustments are the carburetor’s air/fuel mixture. A mixture which contains too much air will cause the engine to hesitate upon acceleration and potentially destroy the pistons. A mixture which contains too much fuel will decrease the engine’s power. Fortunately, the carburetor need not be disassembled to adjust the mixture.
Turn the engine on and allow it to warm up.
Locate the two large slothead screws at the bottom of the front of the carburetor. These are the air/fuel mixture screws.
Turn one air/fuel mixture screw in a clockwise direction with a slothead screwdriver with the engine idling until the engine speeds up. If the engine instead slows down, turn the screw in a counterclockwise direction until the engine speeds up.
Turn the other air/fuel mixture screw in a clockwise direction with a slothead screwdriver until the engine again speeds up. If the engine instead slows down, turn the screw in a counterclockwise direction until the engine speeds up.
Adjust the throttle idle screw to the desired idle speed. Because adjusting the air/fuel mixture to its proper setting causes the engine speed to increase, the speed at which the engine idles may have to be lowered. The throttle idle screw is a slothead screw located on the driver’s side of the carburetor. Turn the screw in a counterclockwise direction to slow the engine’s idle speed.