Engine is dieselling

[dana a]

ACF. The reason suggested cleaning your engine off is because I bought a used Toro with a twin cylinder Krohler engine and it had an oil leak and the oil collected a lot of dust while leaking oil. I'd be mowing 3 or 4 hours at a time and if I didn't let it idle to cool off some it would set there still running with the key off and making all kinds of knocking noises till it stopped. After I took the engine out and fixed the oil leak and cleaned the engine I could mow for several hours and turn the key off and it quit running like it's supposed to. All the dirt and crud insulates the engine and makes it run hot and when I'd turn the key off it was so hot that the gasoline fired from the heat left in the engine and ran like a diesel. Yours may be doing the same thing.
sgkent and hammermechanic also told you over heating would cause it to diesel.

 

[ACF]

What is the engine model number? Can you post a pic of the spark plug and what is the numbers of the plug?
When you sad dieseling is it running on when you turn the key off or just kicking backwards once when you turn the key off?

 

[Hammermechanicman]

That plug is good. If the engine was overheating to the point of dieseling from an overheated plug the insulator would be white.
Does the engine need to run for a while before it diesels or will it do it after just a couple of minutes of running?

 

[ACF]

That plug is good. If the engine was overheating to the point of dieseling from an overheated plug the insulator would be white.
Does the engine need to run for a while before it diesels or will it do it after just a couple of minutes of running?

needs to run for a while over an hour at least

 

[Scrubcadet10]

Get an inline spark tester, and put it on and fire up the mower. When you shut it off, see if there is spark still present while the engine is dieseling.

 

[Hammermechanicman]

Sounds like a carbon hot spot. I would pull the head and decarbon it.

 

[ACF]

Get an inline spark tester, and put it on and fire up the mower. When you shut it off, see if there is spark still present while the engine is dieseling.

no spark when engine shut off after running for 1 hour just turning backwards and making a loud bangging noise like something is going to come side of engine

 

[sgkent]

with the engine running at a high idle e.g about 1/2 speed, drizzle/spray with spray bottle some water into the carb - drizzle/spray with spray bottle not pour. The drizzle will make it run rough, if so open the throttle a little more to keep it running. You do not want to use so much that it stalls. But if it stalls STOP drizzlingspraying. It is a dance between the amount of water and keeping the throttle open, try not to let it stall so it is Ok to stop pouring (or spraying if you have a good spray bottle). I let the trickle be like a small trickle coming out of the faucet. Again, the goal it to get the water thru with it running and not stall it. The water will turn to steam and knock carbon off the piston and head. It is Ok to stop pouring/spraying and get the engine back up to speed before adding a little more moisture. It is the GM approved method for knocking carbon out of an engine for years. Some folks add a teaspoon of brake fluid to a pint or so of water to make it easier on the engine. A 1/2 small beer bottle full of water is about what it takes, even a few sprays at a time to avoid killing the engine. See if that helps. If not the head comes off and the piston and head get cleaned as suggested. Change the oil afterwards because it will be dirty with carbon. If you have ever seen an engine that had a head gasket to a water chamber go bad the piston and head are clean and white due to the water knocking the carbon off when it turns to steam.

ALSO make 100% sure all the fins and blower etc are clear of grass and dirt, and that it is not causing the head or cylinder(s) to overheat. IF YOUR ENGINE HAS A CATALYTIC CONVERTER DO NOT USE THIS PROCESS.

 

[ACF]

to all thank you for all the help in trying to resolve the issue with the engine i was working on. did it the engine running the correct way. i disconnected the fuel solenoid and the mower kept running, turned off engine removed fuel solenoid and found someone had cutoff the end of the fuel solenoid. replaced the fuel solenoid started the engine ran it for 2 hours turned the engine off no dieseling or noise. not sure why this fixed it but it did.

thanks aall

 

[Scrubcadet10]

good deal