I am running a recently rebuilt Autolite 4100 carburetor and the stock Duraspark II ignition system in my 1985 302.
I warmed the engine up and set the idle and the dash pot at 750RPM. It idles great here, until I take it for a spin. When I come back, the idle is up to 900RPM. I give it a quick stab of the throttle, and it comes back to 750RPM. Another test drive, and the same thing happens again. I pulled the air cleaner and it appears that the throttle isn't returning all the way to the dash pot setting. If I manually push the throttle arm down to the dashpot, it idles fine again at 750RPM.
I take it for a spin again, and the same thing happens. Frustrated, I turn it off for about 30 minutes. Go back to start it, and it stalls immediately. Try it again and the engine starts right up but now it is idling low at 500RPM (but touching the dash pot that was previously set at 750 RPM) and is about ready to stall. So I give it some gas and the idle comes back to 750RPM and stay there until I drive it again or rev it up high and then it wants to idle at 900RPM again. I have to give the gas a quick stab again to get the throttle to return to 750RPM.
It was running perfect until yesterday, and the engine was rebuilt only a couple of weeks ago.
What in the heck is going on with this thing?