What Makes My Carter AFB Idle Too Fast?
- Idle Speed Adjustment: The idle speed screw might be set too high. This screw controls the throttle plate opening at idle, and if it’s turned too far in, it will allow more air and fuel into the engine, causing a high idle.
- Throttle Plates: If the throttle plates were removed and replaced in the wrong position, there may have too much space between the throttle plate and carburetor bore wall. The throttle plates opening up is what makes the RPM increase.
- Vacuum Leak: A vacuum leak would make it idle fast. Use spray carb cleaner to spray around the throttle body and any other vacuum source. If the RPM changes, then there is a leak. A vacuum leak can cause the engine to run lean and the idle speed to increase. Common sources of vacuum leaks include the intake manifold gasket, carburetor base gasket, or vacuum hoses that may be cracked or disconnected.
- Linkage : Disconnect the throttle linkage to the carburetor and run the engine. If that makes a difference then the problem is in the linkage. May bent, or mall adjusted.
Look at the fast idle cam to make sure when the engine is warm and choke is off that the idle screw is on the lowest point of the cam.
- Secondary Throttle Plates Sticking: On some Carter AFB carburetors, the secondary throttle plates might stick slightly open if they are not adjusted or aligned properly, leading to a higher idle speed.
- Secondary Opening When Cold: Is the dog in position to lock out the secondary when the choke is closed?
- Incorrect Timing: If the ignition timing is set too far advanced, it can increase the idle speed. Double-check the timing to ensure it’s within the proper specifications for your engine.
- Carburetor Dirt or Debris: Dirt or debris in the carburetor can interfere with proper operation, such as the idle circuit. This could cause the idle to be too fast if fuel or air passages are partially blocked.
