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Snapper backfires Please help

Discussion in 'Mechanic and Repair' started by Haake, Jul 31, 2014.

  1. Haake

    Haake LawnSite Member
    Posts: 20

    I have a snapper riding mower and after it runs for a while it starts backfiring and smells burnt... Any help would be appriciated.
  2. OptsyEagle

    OptsyEagle LawnSite Member
    from Toronto
    Posts: 13

    Will need an engine brand and model number.
  3. hal

    hal LawnSite Member
    from Georgia
    Posts: 45

    How old is it? When was the last time of tune-up? Could be as easy as spark plug fouling, or ignition module over heating, plugged gas cap, dirty air filter, broken plug wire, rings,........ Try some of these first. Fresh gas?
  4. Haake

    Haake LawnSite Member
    Posts: 20

    Would adjusting the idle throttle have anything to do with it? Or the needle valve? Its over 15 years old btw
  5. Haake

    Haake LawnSite Member
    Posts: 20

    Briggs and Stratton
  6. OptsyEagle

    OptsyEagle LawnSite Member
    from Toronto
    Posts: 13

    Most backfires are fuel igniting inside the exhaust cavity. Perhaps your exhaust valve is not closing enough allowing fuel to enter the exhaust and ignite. I would try to get a look at the valve clearance. Your exhaust valve should have a clearance between 0.009" and 0.011". If the clearance is too low or there is no clearance at all, it can prevent the exhaust valve from properly closing.
  7. Patriot Services

    Patriot Services LawnSite Fanatic
    Posts: 12,441

    Exhaust valve is hanging after heat expansion. Either the lash is closing or its hanging up and not seating.
    Posted via Mobile Device
  8. JimQ

    JimQ LawnSite Bronze Member
    Posts: 1,139

    Sounds like valve issues but also check the throttle shaft for excessive clearance. They wear, suck air, and cause the engine to run lean.

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