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Just curious why I get the backfire

Discussion in 'Mechanic and Repair' started by Craftybigdog, Jul 25, 2002.

  1. Craftybigdog

    Craftybigdog LawnSite Senior Member
    Posts: 425

    I have a john deere with a 25HP Kohler gas motor and when you shut it off it backfires everytime I have looked in the manual and it doesnt have adjustment for the timing any ideas!
  2. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    that's common on the kohlers when you idle it down then shut it off. shut it off at 3/4 to full throttle and that will do it.
  3. Ax Man

    Ax Man LawnSite Senior Member
    Posts: 446

    Yup, try shutting it down at half throttle.
    I had the same trouble and someone else told me.
    Good luck
  4. lschultz

    lschultz LawnSite Member
    Posts: 11

    I had a cheap Husky with a tecumseh 15.5 and it would do that.I read on here to let it idle a bit before you shut it off.I tryed that and it works.
  5. grasmo

    grasmo LawnSite Member
    from fl
    Posts: 34

    shultz is right. let it idle longer to let it cool down more before shutting it off. if you shut it down at high rpms you are cooling it down with excessive fuel which is also washing the oil off the cylinders. check to make sure the blower housing and the cooling fins are clean. you could also try the coolest spark plug they make.
  6. Ax Man

    Ax Man LawnSite Senior Member
    Posts: 446

    Actually the Kohler owners manual, My Walker manual both state to shut down at half throttle.
    Letting it idle down for a minute or so is a good idea, but htn give it a little juice and shut it off.
  7. olfrt

    olfrt LawnSite Member
    Posts: 48

    These new carbs and emission control cause the motors that have to meet them to act diffrently than the older style carb.

    We use to say to idle the motor down and cool it off (so the fuel would not wash the oil of the cylinder wall during shut down).

    Now the fuel shut off is engage as soon as you turn the key off. Also the engines run hotter because of leaner fuel requirements in order to meet emissions.

    Shutting down with the throttle at 1/2 or slightly higher is the ticket on the kohler motors now.

  8. grasmo

    grasmo LawnSite Member
    from fl
    Posts: 34

    so mine should shut off immediately as soon as i unplug it then right? i wonder why it doesn't.
  9. olfrt

    olfrt LawnSite Member
    Posts: 48

    The fuel shut of solenoid is suppose to serve more than one purpose. Some times it is called an anti backfire solenoid.

    When you turn the key off the juice (12V) is removed and the plunger pushed into the seat or main jet to stop fuel flow.

    This prevents most of the fuel flow after the key is turned off.

    With the new large mufflers needed to reduce noise they would collect fumes and would issue loud backfireing a few years ago.

    Now if yours is running on after you turn the key off a couple of things could be wrong.

    1. the heads have a lot of carbon build up (not normaly the culprit in todays engines due to clean burning)

    2. The fuel solenoid is not seating because the jet has on it burr, is dirty, or the plunger is weak.

    if you have changed your fuel filter a small piece of the fuel line could have gotten up to the fuel shut off.

    there other things that could cause this. With out seeing the machine I am only guessing at some of the possible problems
  10. olfrt

    olfrt LawnSite Member
    Posts: 48

    By the way

    Assuming it's a new machine it should be under warranty

    One other thing that happens when you turn the key off the magneto is grounded (ignition). This kills the engine fast.

    If the ignition is not grounded then the engine will run for a short time before it dies on the residual gas.

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