ddwood50

Hey forum members. Need some advice and help. Got everything working decent on my 76 with exception of one item. When i shut down the engine will diesel on me. Checked timing, set at 12 TDC per manual. The only thing is the previous owner has put aluminum heads from an 81 on here. This is a 350. Anybody got sugestions on what else I can do to stop this?

Big Fish

If the idle speed is set too high this could happen. Also if the carb has some problems which causes you to set the idle screw high enough where the throttle plates are opened slightly. Some of the earlier years had an idle stop solenoid so when the ignition switch was turned off the solenoid would release and cause the throttle plates to nearly close.

dogboy

I vote for carb problems. I had this happen also with the q jet. Idle was set to high to compensate for cam and would run on for a couple of seconds. I need a carb rebuild ,or change, and it will once in awhile still do it. I think the vents are not closing all the way and sticking sometimes. The motor is like new with 23K miles and no carbon build up at all. Still has the original 1977 q jet!

SanDiegoPaul

If it is a Q-Jet, then look for vacuum leaks around the throttle shaft. Wiggle it, you should have no play in there at all - and if there IS then it is sucking air. Also as otherwise posted, having a higher than normal idle and/or timing could contribute to this as well.

ddwood50

Carb is a Holley. That is where I am heading toward is a rebuild on the carb. Will try a higher octane fuel and run it hard on the road first to see if that will cure things. Thanks for the posts.

vettfixr

My 74 has an idle solenoid on it's Q-Jet to set the idle speed. The idea behind it was to completely shut down the carb when the engine was turned off so that it wouldn't diesel. I believe this problem became an issue when mixtures started to go lean due to emmissions. You might want to try to lower the idle speed and richen the mixture a little to see if it helps.