Quote Originally Posted by larjones View Post
The assembler took my old dashpot and accelerator lingage and put it on my new short block. Whats occurring is that the engine idle screw is set to 575 rpms. Now when the engine is turned on it goes to 800 rpms. When I play with the accelerator rod back and forth the engine will drop back to 575 rpms. What could be wrong is it a weak spring on the dashpot or what. This engine is a fe390 into a thunderbird. Thank you Larry. Ps this didnt occur on the old engine at all.


Electric, or mechanical dash pot? The electric type needs to have the idle speed set, with the "solenoid engaged".

The mechanical type just slows the throttle return speed to idle. Check for linkage binding. If it has a kick down rod check that also for binding.
Another thing is the fast idle cam on the choke. It was common for the nylon to deform and bind. Just take it apart and turn it "by hand" on a drill bit mounted in a vise to clean it up.

Best to disconnect everything, and see if it works OK, then add the pieces back on till you find the problem.