Why does my bike backfire???

Discussion in 'Mechanical & Technical' started by A4wheelin, May 28, 2008.


  1. Recently my bike has been back firing when I let off the gas. Sometimes one pop, other times a series of pops. What causes this and how do I fix it? Is it really a big issue? Thanks!
     
  2. Probably a small exhaust leak? Check the joints/gaskets in the exhaust system.
     
  3. I'm no expert but I think popping once in a while is normal. I got an '06 gsxr 600 and it pops when i let off the gas at higher RPMs. Dont know much about carbureted bikes though.
     
  4. My 07 GSXR 1000 does the same after I put an exhaust and power commander on it. I've been told that its just fuel that hasnt been burned and gets into the exhaust and when it gets the right air and heat it egnites. Not sure this is correct or not. I also dont think its bad but the only reason I say that is the one time I went to the track I think most of those guys had the same thing.
     
  5. tophyr

    tophyr Forum Cripple

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    Too rich.

    Have you recent re-mapped/re-jetted/modified your bike in any way?
     
  6. tophyr

    tophyr Forum Cripple

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    A lot of track bikes "burble" when they're off the throttle.. this is different than backfiring. Burbling is a "problem", but track guys don't care about it because it indicates poor off-throttle mapping, and they only usually care about WOT. Backfiring, on the other hand, is a problem.
     
  7. So who can he contact to have his stuff dyno mapped out correctly?
     
  8. tophyr

    tophyr Forum Cripple

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    His F3 is a carb'ed bike, so it might not be worth some intense dyno time. But, given that he's in Portland, EDR is where I'd go.
     
  9. +1
    It could also be caused by dirty plugs. A weak or occasionally missing spark will keep it from burning all the fuel.

    A bad coil could be causing weak or missing spark as well, but usually it is the simplest answer as opposed to some part of the ignition system farther down the line.
     
  10. A couple possible factors:

    A change in back pressure of the exhaust system. (like changing your exhaust or getting rid of a cat. converter if your bike came with one. Higher flow systems generally mess with the fuel mapping of your system causing more fuel to be used and since it doesn't burn completely it gets superheated and pushed out the back) ...which brings me to ->

    Engine not completely burning fuel and upon exiting the exhaust tube mixes with enough oxygen in the air to combust. (backfire)

    Leak in the exhaust pipe somewhere enabling oxygen to enter the system creating secondary combustions (backfires)

    Basically the problem is the engine not completely burning all of the fuel that's pumped into it. "running too rich" If your exhaust smells of gas and you have a lot of carbon deposits this might be the case.
     
  11. been thu this myself and it was a lean condition...
     
  12. Thanks for all the answers guys! I remember it doing this every once in a long while. I couldn't figure out what the noise was though. Now it pretty much happens anytime I let off the throttle. I haven't done any modding or tuning at all. I did run the bike without the exhaust pipe for a day last week. But besides that nothing else has been changed. It doens't bother me any I just didn't know if it would cause any damage or anything.
     
  13. It is likely running LEAN. Take it to EDR and have him check the air/fuel ratio on the dyno. Backfiring is only a SYMPTOM. A lean running bike can also run HOT when the temp warms up, and you can burn valves etc... Backfiring is NOT normal and you really should get it checked out.

    EDR: 503-222-race
     
  14. here are the possible causes:

    1) normal operation or air injection system (yes it is suppose to do that)
    2) free flowing exhaust system (they do that too)
    3) fuel mixture too lean at low speed
    4) fuel mixture too rich at low speed
    5) air entering exhaust system
    6) incorrect ignition timing
    7) water in fuel (will also misfire during acceleration)
     
  15. Grantizzle

    Grantizzle <img src="/images/ranks/mod.gif" alt="Moderator">

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    cause: touching yourself too much

    fix: touch yourself less or touch others more.
     
  16. FastCat

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  17. Kolat

    Kolat emw2k9 beer pong champions

    put the bike in neutral.....

    pin the throttle, when the rpm's get about halfway up click the kill switch off then on :)

    makes one helluva backfire on carb'd bikes, though I've heard of it blowing up motors too /shrug.

    T
     
  18. FastCat

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    Nope, that is not a "backfire" either.

    ...although it's very LOUD.
     
  19. You Sir! ...are a very bad influence...:bonk
     
  20. FastCat

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    (poppity-pop-BANG-pop-pop,poppity-pop)

    ...nope... that's not a backfire.

    [​IMG]

    ...now, THAT's a backfire.
     

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