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PK.
PK., Small Engine Technician
Category: Small Engine
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Experience:  Retired Owner of a full service shop and national parts sales website.
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I have a John Deere snowblower and the engine revs up and down

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I have a John Deere snowblower and the engine revs up and down (surges). It starts fine but won't idle slow. When you idle it down it surges back and forth backfires, and dies. The exhaust smells very rich. I tried to adjust the carbs main jet and idle screw out 1 1/2 turns. Removed the carb and cleaned the bowl, needle and float. It had a bit of tarnish but nothing serious. Co-worker suggested the governor is messed up. What do you think?
Submitted: 5 years ago.
Category: Small Engine
Expert:  PK. replied 5 years ago.
I think you were right when you suspected the carburetor. If you hold the governor rod, will the engine die?
Customer: replied 5 years ago.
If you hold the governor back it will die and of course it will run faster if you hold it the opposite direction.
Customer: replied 5 years ago.
Are we still trying to figure this out or are we done at I think it's the carb?
Expert:  PK. replied 5 years ago.

Sorry, I was answering someone else. It can take a few minutes for me to get back to you.

 

If you hold the governor rod so that the throttle is at normal operating speed and the engine dies or surges, then it sounds as though the carburetor could stand a good cleaning. I'm assuming it does this with the air filter off? It only takes a speck of dirt in the wrong place to cause a carburetor to malfunction. What you can try is to spray a little carb cleaner in the carburetor with the engine running and see if that helps smooth it out. If it seems to help, then a product like SeaFoam used per the label might be of help. This may save you from having to completely rebuild the carb.

 

If holding the governor stops surging, it could still be the carburetor, but also could be an internal problem with the governor. Since the carburetor is cheap and easy to work on,. I'd eliminate that as a source before I moved to the governor.

 

 

Customer: replied 5 years ago.
i don't think there is an air cleaner on this machine. I have put a little sea foam in the fuel.
Expert:  PK. replied 5 years ago.
Did you try the SeaFoam straight into the carburetor?
Customer: replied 5 years ago.
no- what about the gasket between the carb and intake? Could that make it surge?
Expert:  PK. replied 5 years ago.

I'd try that. I forgot to ask, which engine is this? If the SeaFoam doesn't help, then I'd pull the carburetor and check the float level. While I were at it, I'd go ahead and give the carb a good soak in a tub of cleaner and put a new kit in it. As there was some sediment in the bowl, it's a safe bet that there's more. All it takes is for an air circuit to be partially clogged and you'll have your problem. Also a leaky intake gasket can cause this sort of trouble.

 

After being completely satisfied the carburetor is okay, then your two options are to check the head, valves and head gasket and the governor. It's fairly uncommon to have a governor malfunction, but it does happen. Let me know what you get with the carb and we'll go from there. Thanks, PK.

PK., Small Engine Technician
Category: Small Engine
Satisfied Customers: 1038
Experience: Retired Owner of a full service shop and national parts sales website.
PK. and other Small Engine Specialists are ready to help you
Expert:  PK. replied 5 years ago.

I just saw your edit. Yes the intake gasket can cause this. If the carb was off and a new gasket wasn't used this will cause a surge.

 

You can check it by spraying some carb cleaner at the mating surfaces with the engine running. The engine will speed up or die or smooth out when you do this if there's a leak.

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