Stall and Backfires - Needs Expert Help

Discussion in 'Mechanic and Repair' started by MOTES, Aug 8, 2007.

  1. MOTES

    MOTES LawnSite Member
    Messages: 90

    Hi guys, I have a problem with my Exmark Lazer Z with 27 hp. Hoping someone on here can help me out. The problem is the mower backfires after slowing down at or getting ready to go reverse. It does it more on a small grade lots, going down and getting ready to turn, almost want to stall then backfires. This backfire is unpredictable. Sometime it doesn't't backfire but want to almost stall out. It have stall completely a few time. I've replace sparks plug. Check the fuel pump. Check Air filter. Replace fuel filter. Taken carbuator apart to clean out any dirt or water that may be in there. Even put in higher grade gas (89) after shop recommended. I know most of us use regular. Everything looks good but still can't figure it out why it still doing it. I am running out of option and hoping you guys can throw me some ideas, thought, comment or anything. I'm starting to lean toward a bad carbuator because that my only thought left, that's why i'm here, i don't want to have to buy a new carbuator if it's something else. The engine have almost 450 hours on it. I must say, Taken the spark plugs out , It looks too lean (not getting enough gas). The gap is at 30 which is recommended. Again, please let me know what you think.
  2. MOTES

    MOTES LawnSite Member
    Messages: 90

    Please help
  3. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 956

    I think it points to 2 possible things-
    1 You have water in the gas (bottom of carb bowl) and the engine gets a "sip" of it when it gets tilted or direction gets changed quickly. Try a few oz of Gas Dri per tank.
    2. "Shifting" of the frame/seat is causing a marginally adjusted safety switch to "do it's thing".
  4. The Captain

    The Captain LawnSite Senior Member
    Messages: 607

    Does the carb have adjusting screws for the mixture" and what about the idle speed? I Think you're on track with it being a carb/fuel problem. Just a guess as to the solution.

    Good luck and let us know how you correct it.
  5. MOTES

    MOTES LawnSite Member
    Messages: 90

    Bill and Captain, the carb be taken apart 4 times and been spray down, so there's no water. Water was the very first thing came to mind, but problem not solve. Carb is Clean Clean Clean. The second thing you mention is the frame/Seat......This was also checked out still nothing found. Alot of the lots are smooth, so it does alot of it backfireing or stalling as you getting ready to slow down or reverse. I'm not a rough driver so i take an easy with it, i'm not falling out of seat. Captain, the carb does not have screws for the mixture. Bill, i did stop by the shop and have them look at it, the mower was running, they can't see the problem since the problem is not happening right there. But at some point at the time, I think i overheard that they mention about the Accerlater Pump may be sticking, but then nothing was said anymore about it. I'm not familiar with Accerlater pump, but if i think about it, if you going full speed one way to the end of lot then pull back to slow down and revrese, can the accerlater pump be sticking and making it backfire or stalling? Please, let me know if there anything else that i can check, I'm up for anything. I pretty much done everything, but missing something simple such as the accerlater pump sticking or the whole carb (which i hope i don't plan on buying unless i have to). Hope to hear from you or anybody again.
  6. MOTES

    MOTES LawnSite Member
    Messages: 90

    Bill, I've also done the gas-dri to clean out the system last week, still nothing.
  7. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Messages: 1,164

    This is a Kohler 27 hp? ( No engine #s posted). If this is a Kohler, and it does have an accelerator pump then I would check it, but most that I Have seen fail make the unit run very rich not lean. I would check for intake leaks were the pipes connect to the heads. Spray (carb spray) around this area while the unit is running and see if there is a difference in how the engine runs.
  8. John Stiles

    John Stiles LawnSite Member
    Messages: 42

    Seems to me the governor could be adjusted up a tiny bit, and it would take care of the problem....~john
  9. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    In some cases backfire is caused from inter-minting spark (a spark plug skips a fire process).

    Given the fact that this only happens when on a incline/moving forward to reverse brings this to mind;

    Some OEM's install a mercury switch on the engine to kill the ignition should too steep of a incline is tackled or a roll-over occurs.

    It looks like a over-sized black pill capsule and has two black wires coming out of one end. On Kohlers it is mounted to the flywheel cover screw just above the starter.

    Check your unit for one of these, Make sure the wires are facing STRAIGHT up. I have seen these installed spun more sideways from tightening the screw and the slightest incline or jerk cause the mercury to kill spark.

    We all know how easy mercury moves around.

    Just a thought.....
  10. John Stiles

    John Stiles LawnSite Member
    Messages: 42

    Ah, yes...the evil bank angle sensor!:dancing: :) ~john

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