Hey Z people, What could be causing my L28 w/ SU carbs to deisel after I shut it off. Is it a vacume leak? If so from where? Help!

Matt-

Look at your timing. That can couse this problem. It could be a number of thangs.

you mean engine run on right?

I have noticed when running a bit rich it can do this but as Bill says ignition timing is another cause.

Too far advanced which causes it to run hotter will cause small imperfections in the cylinder head to glow like a glow plug in a diesel and cause it to fire after the engine has stopped.

If it does this drop the clutch as the motor can actually run backwards running the oil pump in reverse and well u know what.

edit: you could be right about vacumm leak check the intake manifolds. Seals , gaskets aswell.

the timeing is about 17 degrees addvanced. Is that to far? I don't think Im running to rich. The nozzels are about 11/2 turns down. Would an exaust leak at the Y pipe on my header cause that?

Also it only does it very intermitently. Could a leek in the vacume addvance dashpot cause this.

Matt-

I had a pretty bad exhaust leak at the exhaust flange and my run on was pretty bad. After changing the gasket there was still a slight leak due to a warped surface on the exhaust manifold, but I don't have run on any more. So yes, I do think it could be a leak at your down pipe.

The run on happened to me the most when the engine was hot. Sometimes it would last for a few seconds.

Ben