High Idle problems

[steveplym]

Wondering if any of you have run across this problem. My '47 plymouth continues to have a high idle problem. I recently had the carb rebuilt and the vehicle starts up fine, once it runs for 15mins or so, or it is driven, it will start to idle very high.

I've checked the throttle linkage and moved the spring around to tighten up everything. No problems there. Marked the idle screw and idle/air screw to make sure neither was turning to increase the idle. Nothing there either. Lastly I have checked for a vacuum leak. None noted. I have turned the idle screw back down after I drive it to decrease the idle. It will idle down, but after I drive it a little while farther it will run the rpms right back up.

Is there anything in the carb that would cause this type of problem if not installed, seated, etc, correctly? I know there is a step up valve in the carb, if it is stuck or not seated right would that possibly cause this condition?

Any help would be appreciated. I'm going crazy trying to figure this out.

[Guest Nelsons Ply]

Steve next time it does not idle down reach down and pull back on the pedal.

that is what i found to be the problem once.

gromet to tight or off center maybe.

maybe the return spring is not tight enough.

Good luck on the fix

[greg g]

Assure that you high idle cam is in its park position. If it is loose it might be bouncing to a positon that contacts the idle screw.