Motor is running backwards after shut off?
 

I went for a short cruise with the G/F last night and she wanted to stop to enjoy the sunset. So I back off plane and kick it into nuetral, I let it idle for about 10 seconds and turn the key off. The motor did the sputter cough, sputter cough thing a good five or six times before it quit. Whats going on here? The temp was around 60-65 outside and kinda damp. I turned the key on to check the temp and it was right at 150 degrees where it should be. The motor is a box stock hp500 non EFI. Whats the cause of this?

I'm thinking you may have some carbon buildup in the cylinders.

How old is your gas?

BAD FUEL?? Are you still on the winter tank?

No I am not on the winter tank, but maybe I just bought a bad batch. I guess it could be carbon build up too. Maybe I should go dump some 104 in it see if it clears up.

Be careful. Dieseling can cause the engine to suck water back into the cylinder when it kicks backward, leading to hydrolock. If it is hard to get it to turn over after this happens, best bet would be to pull the spark plugs and remove the lanyard before turning it over a few times to dispell any water that might be in the cylinders. Hydrolock can result in extensive engine damage.

Ive seen where 1 cylinder will get some pre-ignition or detonation on the shutdown, and if in the piston\crank are in the right (wrong) spot, the motor can start to diesel backwards. ive seen it happen in a friends (crappy) car, and it is hell to shut it down if it doesnt stall right away.

This is what I was afraid of, I'm going to make sure I have a plug wrench in with me next time I go out

Why do you think it's going backwards? Sounds like run on (dieseling). Usually due to low octane gas, high compression (carbon buildup?), to much ignition advance, or too high idle speed.
Check it all out. If it's dieseling at shutdown, it's probably detonating under load too.
Gary

You were definitely dieseling, we had that prob in one of our Apaches. Check your carb setting also