Technical motor run on (dieseling)

I have a chevy 350 crate motor, mild cam,edelbrock intake and carb, AC spark plug 43ts, gap 45%, HEI dizzy, timming 6%. and it runs on when I cut it off what wrong.

 

Main causes of dieseling are carbon buildups in the cylinders, running low octane fuel instead of higher octane, or having the idle speed set too high.

 

Or alternator feedback. What alternator are you running, and how is it wired?

 

Could be several things
Is this a new problem, meaning it ran fine before
Or
Is this a new engine start up and nothing has proven itself?

Basically, there's enough heat on something to cause the air fuel mixture to ignite.
You'll need to either find and control the heat or find out why there's enough air fuel to ignite in the first place or a combination of both to correct it.

 

been running fine just started,

 

Does the engine have Vortec heads and if so-have you plumbed in an external water by-p***?

 

If you didn't change anything,
it may just need a tune up.
Something have came out of adjustment
You may have just got a carbon deposit built up large enough to get hot enough
You didn't touch anything ?
New problem shows up - go back to the last thing/s you did

 

The easiest way to avoid "run on" if not able to really fix the problem is to cut the key off while in gear,don't kill the engine in park or neutral ,or just let out the clutch while in gear.

 

Maybe you got some bad gasoline. Try an octane booster additive.

You could add an anti dieseling solenoid. It holds the throttle open at idle speed while the key is on and allows the throttle to close when the ignition is turned off.

 

Too rich of a mixture, high idle speed, too much base timing, vacuum leaks can all contribute to the problem. Poor fuel quality can also be a factor

 

How big of a carb are you using? CFM.... Vacuum secondaries or double pumper?

 

I find that most of the time it is carbon buildup. Mostly because the cars are set a little to rich, over time it causes build up. I usually use Seafoam to clean it out. Follow the instructions on the can.

 

I can go with bad gas especially if it happened suddenly. Try a tank full of 93 octane first. I buy my gas locally from 1 or 2 stations.

 

Had this problem on an OT car and it turned out to be a leak between intake and heads.


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Check the distributor hold down...it could be loose...especially if it is a chrome one....I had the same thing happen on the Roadster I traded your Dad.....back the timing down a little more.....I never use a timing light on a street car engine..........I adjust it to where it cranks good and cuts off good.......also idle may need to be backed down a tad.........timing is the culprit....this gas today needs lower timing.