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I have a 12.5 HP Kohler on my JD. I replaced the old gas,spark plug and cleaned the carb, but when I try to start it, I get a backfire through the exhaust. Removing the plug reveals oil on the plug and the smell of gas. I know my carbs getting gas but am not sure if it's reaching the cylinder. I'm getting plenty of spark but it will not start, just backfires. Should I rebuild the carb?? Help.....
 

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its hard to say without being there but it sounds like the float in the carb is not shutting off or maybe gas got in the oil and may be coming through the crankcase vent into the carb. If it ran ok before you would assume that the timing and valve train are ok and could be a carb problem
 

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I would do a compression check, If it is back firing while trying to crank it sounds like a valve isnt closing and letting the compression through the exhaust. My 15 hp kohler has a compresion release to allow for easier cranking. Could it be that this is stuck in the open position??? come on guys help us out here
 

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Could be several things. Since it was running ok last year I would try a new plug first since that one is oil soaked. A compresson check would not tell much since it has a compresson release. Change oil for sure. If it still wants to backfire you may have to pull head and see whats going on. As a friend of mine would say, It will be OK!
 

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I am not sure what the minimum compression is with a compression relief. But if it is below the minimum compresion reguirements then that might indicate a problem, does anyone know how much compresion it takes for a kohler to crank properly??
 

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I agree with VegativeSteam, I would pull the flywheel to check the key before pulling the head. Normally when a key shears the timing will advance causing a backfire through the intake. Its not often the key will shear to ****** the spark but stranger things have happened.
Note: When pulling the flywheel, use a puller and DO NOT use a hammer. The charging system magnets are glued in and you risk knocking them loose if you use impact.
COMPRESSION
The engine has a compression release but you should still get about 100psi. If the compression release is out, compression can reach 180psi.
A leakdown tester is the best way to check the engine. If compression is low the tester will help locate where to find the problem.
 
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