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Backfiring engine

Discussion in 'Mechanic and Repair' started by slytiger, Jul 1, 2001.

  1. slytiger

    slytiger LawnSite Member
    Posts: 3

    I've got a 12HP B&S engine on a Lowes/MTD riding mower. Periodicaly the engine backfires when I go around a corner, or when I disengage the blades and put the mower in neutral. Is this normal? This sort of thing happened to me before, and the engine ended up throwing a rod. I don't want that to happen again, any preventive advice, checks?
  2. ron

    ron LawnSite Senior Member
    Posts: 312

    Ok try this
    1.lower your RPM before shutting off the engine.
    2. turn fuel shut off valve next to you gas tank and let the motor run itself out.
    This works great for me with my Scag 36 in WB
  3. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    Or you can lift the battery up, slide the riding tractor out from under it and slide a commercial mower under it that has a real engine. Drop the battery into the commercial mower and wham, problem fixed.
  4. MrFikit

    MrFikit LawnSite Member
    Posts: 28

    What sounds like is you may be getting an excess of fuel into the combustion chamber. What would normally cause this is the wrong float bowl setting. Get yourself a nice manual on 12HP Briggs engines and it will tell you how to go about doing it. Normally, you just remove the carb, remove the bowl on the bottom, turn it upside-down, then measure the distance between the bowl mounting surface and the bottom (in this position) of the float (usually not more than maybe 1/4" to 3/8") look at the book. There is a tab at the pivot side of the float which controls the depth of the needle valve. If you insert a screwdriver into or under that tab and bend it, you can achieve the desired height. Also, it never hurts to keep-up with regular maintenance such as spark plug, air cleaner, etc. Hope this helps.
  5. Fish

    Fish LawnSite Member
    Posts: 139

    Sounds like a layer of water in the bottom of the carb bowl. Dump
    it out and see what happens.
  6. Fish

    Fish LawnSite Member
    Posts: 139

    Also could be that the kill wire to the switch at your forward
    /reverse lever is has come unplugged and is close to metal.
    Take the two phillips screws off of the panel and lift it up and
    see. The seat switch is another problem area .
  7. williamslawn

    williamslawn LawnSite Member
    from SC
    Posts: 202

    Sounds like the seat switch to me.

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