Originally Posted by
David T
Somehow, someway, more air is getting past the throttle plates. It could be leaks, it could be the decel valves not closed all the way, maybe the throttle plates have been deformed or bent, or the idle motor isn't working correctly. More air lets the motor run faster. Leaner for sure but also faster. Also check that the vacuum advance is working correctly. If it is not hooked up right or isn't working it can affect the idle speed. Check it electrically and with the vacuum. Make sure all of the hoses are hooked up to the correct ports and none of the hoses are cracked or split.