Kohler 25 HP Misfiring

Discussion in 'Lawn Mowing' started by mvgerb, Jun 3, 2003.

  1. mvgerb

    mvgerb LawnSite Member
    Messages: 6

    My Gravely 260Z with Kohler 25 HP is misfiring at full throttle.
    Backfiring through the airbox. Checked carburetor, plugs, air filter, and fuel filter however problem continues.
    Also had both head rebuilt, and problem began shortly thereafter!
    Runs well at half throttle. Any info would be appreciated
  2. 1 plug white and one plug black?
  3. EJK2352

    EJK2352 LawnSite Bronze Member
    Messages: 1,150

    Maybe a bad coil or an incorrect coil air gap setting?? Maybe a smart box going bad???
  4. Coil going bad has no in between, it goes then that side does not spark. It can come and go, but it won't pop, it will just sound funny and loose power.

    Coil gap setting maybe, could, possibly.:confused:

    Smart box; what's that?

    Possible items to check:

    Low octane or bad fuel
    Dirt in fuel line
    Dirty fuel filter
    Air cleaner dirty
  5. EJK2352

    EJK2352 LawnSite Bronze Member
    Messages: 1,150

    Smart box is another name for the spark advance module on most 25 HP Kohlers.
  6. ducky1

    ducky1 LawnSite Senior Member
    Messages: 252

    Kohler Commands sometimes need a multi wt oil for the lifters to work right. Was the oil changes when you had the heads repaired?
  7. Jman

    Jman LawnSite Member
    Messages: 217

    When the heads were done did they grind the valves and seats both? If so did they measure valve stem height before and after and then grind the end of the valve off so it was at the same height it was originally? Most shops miss this point. Kohlers do use a hydraulic valve lifter and the rocker arm is none adjustable.
  8. Grassmechanic

    Grassmechanic LawnSite Silver Member
    Messages: 2,697

    backfires through the intake usually indicate valve problems.


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