what causes dieseling?

My D-19 gas does a funny thing, when I shut it off it keeps trying to run and then finally backfires or spins backward and puffs smoke out the air cleaner. Any idea what causes that? It doesnt always do it, and runs fine otherwise. Thanks
 
My Husky mower and 550 Oliver will do that if I don't let them run about five min. idle to have a little time to cool off after working hard.
 
Idle it at 400 RPM for one minute before shutting off the key when HOT. Yes.....400 RPM. The hotter it is the more idle time you need.
 
(quoted from post at 19:44:10 10/27/16) My D-19 gas does a funny thing, when I shut it off it keeps trying to run and then finally backfires or spins backward and puffs smoke out the air cleaner. Any idea what causes that? It doesnt always do it, and runs fine otherwise. Thanks

Dieseling is caused by heat in the combustion chamber. Assuming the tractor has not been modified by increasing the compression ratio, adjusting the idle speed should cure it. The goal is to allow the combustion chamber to cool at idle.

Check and adjust the timing, retarded timing requires a greater throttle opening to maintain idle speed. A greater throttle opening means more heat in the chamber. Check and adjust the idle speed. A low idle speed is desired which increases the time between combustion events allowing more time for cooling.

Gasoline also plays a role with the higher octane grades being more resistant to dieseling. Regular grade gasoline (87 PON) should be fine in a tractor. If a higher grade is required it could indicate (IMO) a specific ignition source within the chamber that should be addressed.
 
thanks for responding, interesting, it has a lower idle speed than Ive ever seen, you can just cut the throttle and it just purrs barly turning over. Il check timing though. Thanks!
 

Have you changed from a Generator, to an Alternator recently..??

You may have a need to put a Diode in the output lead to prevent just this sort of thing..
 
Even at normal heat range, it is not advisable to just shut it down immediately. That goes for any engine.
 
That's not even remotely close to being a correct answer.

A diode is a one way current device. Install it reversed biased in the output to the bat and it won't charge. Only other option is forward bias, and like this, it wont effect dieseling at all.

Only thing a forward biased diode would remotely help with in the output line would be if the trio had a bad segment and allowed the bat to drain when not running, and it that setup, its a poor poor band aid due to the size of diode you would need.

You are probably thinking about a diode in the excite line to keep the excite line from backfeeding the ignition. Backfed ignitions continue to run normally when you turn the key off.

The op has dieseling.. 2 very different things.
 
I can understand your hostility. If I had posted a 100% wrong answer I would be mad too! :)

Have a good Saturday!
 
dieseling is just what it says... engine running without a spark. SO... to cure this you must remove the fuel. which you do by closing the throttle plate by slowing the idle whch closes the throttle plate. idle has to be less than 400 rpm or just so tractor hardly runs.you can even completely close the throttle plate and use the throttle lever as the shut down. guaranteed it will not keep running. dieseling is caused by hot spots in the combusion chambers. the fuel being sucked in is ignited and makes the engine keep running roughly, basically it has nothing to do with timing or spark. but they should be set to factory spec's to reduce the heat build up.and also idle the engine for a few minutes. very simple fix ... NO FUEL... NO RUN.
 
Agree fully with idle speed. Only add: be sure governor is not pulling throttle back open as engine speed decreases. No fuel in cylinder: no dieseling.
 
this tractor will run with the throttle closed. Its amazing it just sits there and purrs barely turning, Ive never seen anything like it. six cylinders are so cool that way
 

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