dieseling

Scott Blanchard · Apr 17, 2013

I rebuilt the motor on my super C, increased the compression in the process. I have been breaking it in and worked in under load for 30 minute periods. the last two times it didn't want to shut off. The last time I had to choke it to stop it. Someone told me I might have to run higher octane fuel. Is this the problem or is my timing off a little. I run 87 octane and the timing sounds spot on. Or is it something else?

gene bender · Apr 17, 2013

Just stop it in gear. You mite need a different spark plug. This can be a problem when using the hi-dome set-up till it gets used some more. Check the timing how far is it sdvanced.

rustred · Apr 17, 2013

make sure the timing is spot on not just by "ear". sometime it helps to retard 2 degree's. the big thing is to have the idle set as slow as possible and this is the biggest cure. to have the throttle plate close completely is the ideal situation when engine is shut off. the chev trucks had an electric soliniod that did this to cure run on.

teddy52food · Apr 17, 2013

Timing shouldn't be an issue as once you turn off the ign, the spark is gone. How long do you let it idel before stopping? Idel it as slow as it goes for a few minutes.

Bob M · Apr 17, 2013

Scott - As others point out ignition timing cannot cause dieseling since there is no spark to "time" once the ignition is turned off.

Rather dieseling is generally caused by a combination of high compression AND hot spots in the combustion chambers. These hot spots can be carbon deposits, a bit of head gasket protruding into the cylinder or spark plugs that are too hot.

You can try running plugs a heat range or two lower and see if dieseling diminishes. As others mention setting the idle RPM as slow as possible and letting the engine idle for 1 - 2 minutes before shutting down can help a bunch.

Switching to higher octane gas MAY help if the problem is high compression. But if dieseling is from combustion chamber hot spots using 89 or 93 octane gas will make no difference. But it won't hurt anything (except your cash flow...!) to try it.

Finally if all else fails simply put the transmission in road gear then let out the clutch as you shut off the ignition.

dhermesc · Apr 17, 2013

Timing can cause the "hot spots" by being too far advanced which caused excessive heat in the cylinder head.

'If the timing is too far advanced, the fuel will be exhausted prior to the end of the stroke, resulting again in a lack of horsepower, a rough running engine and a quick cylinder head temperature buildup. A too-advanced situation will cause detonation within the cylinder, causing damage to the valves, head gasket and rods.'

http://www.life123.com/cars-vehicles/repair-troubleshooting/ignition/ignition-timing-problems.shtml

Bob M · Apr 17, 2013

Good point! However this situation is usually accompanied by pronounced pinging/knocking under any significant load.

teddy52food · Apr 17, 2013

And kick-back of the starter.

David G · Apr 17, 2013

It is not timing, that is an old wives tale, idle is too fast.

rhtx55 · Apr 17, 2013

+2 on idle adjustment

John G. Hasler · Apr 18, 2013

> the chev trucks had an electric soliniod that did this to cure run on.

So does the IH544.

Scott Blanchard · Apr 18, 2013

Thanks for the advice. I slowed the idle down some and could go a little more. I will work it a little more and see if the problem persists. I'm going to buy some cooler plugs if that happens. I may be back. Thanks again.

dieseling

Scott Blanchard

Member

gene bender

Well-known Member

rustred

Well-known Member

teddy52food

Well-known Member

Bob M

Well-known Member

dhermesc

Well-known Member

Bob M

Well-known Member

teddy52food

Well-known Member

David G

Well-known Member

rhtx55

Member

John G. Hasler

Member

Scott Blanchard

Member

Similar threads