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Garden Tractors Discussion Forum

12 hp Kohler; backfires shuts down

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Jim F.

07-12-2004 04:10:50




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Have a 12 hp Kohler in a Cub 1250, the engine will start run and then after 3 minutes it will start to loose rpm's, backfire and shutdown. Wait a few seconds and it will start and run and do the same thing. Sometimes it runs longer than the next but never over 3-4 minutes.

The carb has been rebuilt, new coil and condenser, when it shuts down there appears to be fuel spitting out the carb. Could the exhaust valve be hanging up?

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Teej

07-12-2004 08:35:30




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 Re: 12 hp Kohler; backfires shuts down in reply to Jim F., 07-12-2004 04:10:50  
Had a 10hp kohler do the exact same thing. Even shot some flame out the muffler sometimes.

Exhaust valve was sticking in the guide.
Yours spitting gas out the carb though, could be the intake valve.

I bought mine that way, cheap. took the shrouds off, found the cooling fins around the valve areas plugged, cleaned it up, put it back together, been running great for 5 years now.

I see you put a new coil and condenser on it, a set of points might help some also.

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Phil B.

07-12-2004 07:15:44




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 Re: 12 hp Kohler; backfires shuts down in reply to Jim F., 07-12-2004 04:10:50  
It's kind of a trait of these motors to have the exhaust valve hang up after a lot of hours. When you take them apart, you'll find carbon baked hard on to the valve stem. The Marvel Mystery oil suggestion works great.



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maek

07-12-2004 06:51:28




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 Re: 12 hp Kohler; backfires shuts down in reply to Jim F., 07-12-2004 04:10:50  
You said it has had a coil and condenser.How about points? they will make it act very wierd when they are bad!?



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R Bedell

07-12-2004 06:35:13




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 Re: 12 hp Kohler; backfires shuts down in reply to Jim F., 07-12-2004 04:10:50  
There could be a number of things causing this to include: Starving for gas, running lean, overheating to mention a few. I would start with the MMO and see what that does. Then I would look at the Carb. Overheating can be from several areas. Blocked fins, obstructed fins on the flywheel blower. All these things are maintenance items that should be checked anyway.

Hope this helps.



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R Bedell

07-12-2004 05:43:56




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 Re: 12 hp Kohler; backfires shuts down in reply to Jim F., 07-12-2004 04:10:50  
You may want to try some Marvel Mystery Oil (MMO)
in the Gas tank and crankcase as indicated by the directions on the back of the bottle. This product has been known to free up sticking valves.



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KennyW

07-12-2004 04:19:19




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 Re: 12 hp Kohler; backfires shuts down in reply to Jim F., 07-12-2004 04:10:50  
YUP



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Jim F.

07-12-2004 06:21:31




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 Re: Re: 12 hp Kohler; backfires shuts down in reply to KennyW, 07-12-2004 04:19:19  
So, both you fellows think that the exhaust valve may be hanging up???



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lucas

07-12-2004 08:09:45




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 Re: Re: Re: 12 hp Kohler; backfires shuts down in reply to Jim F., 07-12-2004 06:21:31  
ive seen a bunch of sticking ex valves on these..usually you can ream or clean out the guide ,clean or replace the valve to fix it.. you should have near 0 compression when this happens... i now use a tablespoon of echo 2 cycle oil per gallon in my cub and it seems to help alot.. used to stick about every 5 years... lucas usmc



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KennyW

07-12-2004 08:56:39




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 Re: Re: Re: Re: 12 hp Kohler; backfires shuts down in reply to lucas, 07-12-2004 08:09:45  
I use Marvel Mystery Oil in my gas mix. Better to take the head off when she quits and confirm it. Any way you decide, a valve job can be done with the engine in the tractor, just put a rag in the breather chamber and ream the guides with a 5/16 reamer, then Lap the valves back in. Kenny



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