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Generator tries to keep running after shutting off

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DeDONRAGE:
What do you think would cause my generator to not shut down properly.  Kind like a car when the timing is off when you shut it down the engine appears to keep trying to turn over.  My generator did this at the end of our trip this week.  It had been running for about 3 hours.  Upon arriving at the house I shut it off.  It was making a knocking sound like it wouldn't shut off.  Started it back up and killed it from the generator itself.  Had to hold choke in to kill it.

I'm hoping to take it back on in the next couple weeks would like to get this fixed.  I have not started it back up yet to see if it does it again.

Rickf1985:
Could be a loose piece of carbon on the head glowing as you shut it down and that is firing the gasoline coming in even though the ignition is off and the plugs aren't firing. Could also be a mouse house in the shroud and the engine is running hot, that would be bad because that would mean it was running very hot for a very long time.

Oz:
Rick... Is this like what people used to call "pre ignition", when a car motor would continue to chug and run after turning the key to the off position, which seemed to be a pretty common issue with cars of the 1960s and early 70's?

DeDONRAGE:
Ive had zero issues with mice.  So thought I cant be 100% sure no mice.  Im going to go ahead and say its not a mouse house.  So what should I do?  Should I start it and see if it does it again?  If it does how should I address it?

Rickf1985:
Normally on most air cooled motors you would pull the heads and clean them and put them back on with new gaskets. the problem here is access, you are talking a MAJOR project to do that on these sets. A trick I have used in the past with everything from little Briggs and Stratton engines all the way up to huge gasoline V8s is water. You will have to have direct access to the mouth of the carburetor so the air cleaner and any hoses will have to come off. You will need a good spray bottle that can preferably squirt water. Get the engine running at normal speed and let it come up to temperature then take your squirt bottle and start squirting the water directly into the carburetor. The idea is to bring the engine speed down some with the water but do not stall the engine. do this for about 5-10 seconds and let it come back up to speed. Repeat this several times and see if the problem is gone. What this does is as the water hits the hot cylinder it vaporizes and steams the carbon off of the pistons and valves. If you keep it at the point where the engine is still running at a good clip and not stalling then you have a good balance and the cylinder is still firing and producing steam. Water is nothing more than oxygen and hydrogen so it will burn when broken down. Do not go overboard with this, a little is a good thing but more is not better. If you try to push it too hard and the engine comes close too stalling and you are still pumping water in you could hydrolock the cylinder, not good! So if it starts to actually stall stop the water.
To give you an idea how this works on a V8 I use a large glass of water and with the air cleaner off and one hand on the throttle linkage I will start giving the engine throttle and start pouring in the water, More throttle and more water. The goal is to keep the engine rpm steady and increase the amount of water as I add more gas. By the time I am at the end of the glass I am close to full throttle and I am pouring a lot faster than you could drink. But the engine is running at about 2000 rpm. If you were to pull the heads off right after that they would look like brand new heads with no deposits on them at all. You can't push an air cooled engine that hard but you get the idea of how it all works. Plus the generators have a preset throttle setting which already holds the throttle for you. I still suggest you take off the upper shrouds just to be sure there are no mouse houses. I have never seen an RV yet that mice have not been in or at least in the outer parts of. Mice are everywhere. just because you don't see them does not mean they are not there.

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