Running on

I ran my tractor hard for a short time a couple of days ago, and it became quite hot so I decided to park it. After I turned the ignition off the engine kept running for quite some time until I turned the fuel off.

I have read that deposits in the engine can cause this. I have a couple of questions:
- Are there any other causes for an engine running on?
- If I have carbon deposits in my engine, will they contribute to overheating? If not, what else might?

Thanks for any insights!

- TS

Hi Pard,

You've answered your own question.

"Dieseling or run-on" is nothing more than a hot chunk of iron that is being fed fuel.

Adjust and slow that idle down.

Allan

Here is a useful explanation from Wikipedia:

Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.

The phenomenon is also referred to as after-run, or run-on when it causes the engine to carry on running after the ignition is shut off, or sometimes dieseling, in reference to the fact that a heated diesel engine may, by design, run without an external ignition trigger so long as a suitable fuel/air mixture is supplied to the cylinders. This effect is more readily achieved on carbureted gasoline engines, as the fuel supply to the carburetor is typically regulated by a passive mechanical float valve and fuel delivery can feasibly continue until fuel line pressure has been relieved, provided the fuel can be somehow drawn past the throttle plate. The occurrence is rare in modern engines with throttle-body or electronic fuel injection, as the injectors will not be permitted to continue delivering fuel after the engine is shut off, and any occurrence may indicate the presence of a leaking (failed) injector.

Preignition and engine knock both sharply increase combustion chamber temperatures. Consequently, either effect increases the likelihood of the other effect occurring, and both can produce similar effects from the operator's perspective, such as rough engine operation or loss of performance due to operational intervention by a powertrain-management computer. For reasons like these, a person not familiarized with the distinction might describe one by the name of the other. Given proper combustion chamber design, preignition can generally be eliminated by proper spark plug selection, proper fuel/air mixture adjustment, and periodic cleaning of the combustion chambers.


I had a similar problem in my Jaguar but I solved the problem with higher octane fuel.

Check your spark plus heat range, ignition timing and fuel mixture before you think about pulling the head off. On old trick of my youth for de-coking an engine was to dribble upper cylinder lubricant down the carby with the engine running. I guess it works - certainly makes a heap of smoke! :lol:

Check that your ignition timing is correct, make sure that the fuel mixture is not too weak, you could have air leaks on the manifold and carb gaskets. Make sure that the fuel is of a good octane rating, (not watered down crap).If you keep running the engine in this condition you will do it harm, so find out what is causing it..John

Check that your ignition timing is correct, make sure that the fuel mixture is not too weak, you could have air leaks on the manifold and carb gaskets. Make sure that the fuel is of a good octane rating, (not watered down crap).If you keep running the engine in this condition you will do it harm, so find out what is causing it..John

if carbon is the problem, you can try seafoam additive from napa which is what is used for outboard motors which are prone to coke up. warm up the engine then pour or spray it in the carb intake so the engine bogs but does not stall until you have used up half a can and then add enough to let it stall. exhaust should emit black smoke like crazy. wait until it cools down then add the rest of the can through the spark plug holes. let it sit overnight. before you start it, put a cardboard box right behind the exhaust weighted in position because it will blast out a bunch of nasty black soot that will stain your driveway / garage wall. for a badly carboned engine run it for a few days then repeat this a couple more times until you get no smoke.

this is not a perfect solution. once an engine gets really carboned up it is very hard to remove the deposits. the only way to safely decoke it is to remove the head and do it manually. an unsafe way told to me by an old mechanic is to add water in the carb intake instead of seafoam. steam works really well at removing carbon but you have to be very very very careful with the amount of water you administer!

Thanks for all the replies. If there's one thing I can say about my tractor it's that I learn stuff!

I'm pretty sure my manifold gasket is good. I will check timing, etc.

What do others think about Semlin's suggestion? I have to admit I am a bit reluctant to try something like that.

- TS

This is what I have used for a lot of years. When the engine is warmed up as much as it is going to warm up,remove the air cleaner hose at the carb. set a pint can of water up on the hood and use a small rubber hose to siphon the water,use a hose that you can pinch off the flow of water. Run engine at near full throttle and hold the hose end in intake of carb while pinching hose to control flow as engine will bog down some as water is injected. The water turns to steam and blasts the carbon away. The price is right. Let engine run a few minutes to make sure all moisture has evaporated.

if you just want to stop the tractor from running on all you have to do is keep tractor in gear when turning off the ignition. then release clutch with foot firmly on master brake pedal. in the 70's our cars would run on and in a automatic we would leave them in drive and turn off the ignition. then place the selector in park. killed them every time.