I've gotten my carb just about running its best although I have this idling problem I can't figure out. The carb is a 4160 VS 750 Holley with a Proform body. It has 70 primary jets.

The car runs slightly on the rich side during driving but VERY rich at idle. If you let the car idle long enough it will blacken the plugs. The car runs its best with the idle mixture screws turned only 1 1/2 turns out ...which is where its fouling the plugs. If you turn the screws in any more the car pops out of the exhaust and runs very rough. The car will stall if you turn them all the way in which leads me to believe there is no internal leak. Its pulling about 15" of vacuum at 1100rpm and 9" while in gear at 750rpm.

I put in a 4.5" power valve to make sure it wasn't opening at idle ...nothing. My floats are also good (just below the sight plugs). I put in 68 primary jets and the car ran like crap. It would break up real bad at part throttle and backfire out of the carb like crazy.

I'm clueless. I'm about to re-install the old main body to see if that helps.... Any suggestions?

Thanks,
Chris

 

Did you try to attain the highest vacuum reading while the car was in drive? Of course you'll need a friend for this but I would adjust the screws this way and see how it acts. Also is your timming set correctly?

 

I set the idle mixture in gear and it still runs rich. Every where else the car runs great. The timing is at 19* initial and about 36* in by 2500rpm. I also set the timing with the car in gear so the load on the motor isn't causing the timing to retard at idle (which was my original thought).