Kohler Backfire

Discussion in 'Mechanic and Repair' started by Chopperman, Apr 12, 2004.

  1. Chopperman

    Chopperman LawnSite Member
    Messages: 1

    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.....
  2. Mikes Machines

    Mikes Machines LawnSite Member
    Messages: 112

    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
  3. grass_cuttin_fool

    grass_cuttin_fool LawnSite Gold Member
    Messages: 3,526

    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
  4. ducky1

    ducky1 LawnSite Senior Member
    Messages: 252

    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!
  5. grass_cuttin_fool

    grass_cuttin_fool LawnSite Gold Member
    Messages: 3,526

    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??
  6. VegetiveSteam

    VegetiveSteam LawnSite Senior Member
    Messages: 296

    Have you checked the flywheel key?
  7. AirCooled

    AirCooled LawnSite Member
    Messages: 30

    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.
    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.
  8. wriken

    wriken LawnSite Silver Member
    Messages: 2,154

    I have a generac 28 hp, that backfires when I shut it down, helps if I let it idle for a couple minutes before shutting off.

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