What causes backfire?

Discussion in 'Engine, Fuel and Exhaust' started by thwart, Jun 29, 2014.

  1. thwart

    thwart Member

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    Newbie here. My 2008 fatboy is starting to "pop" some backfire when I downshift for stops. What causes that? How do I correct it?
     
  2. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    Where's the "pop" coming from? Intake or exhaust? Assuming exhaust, sounds like a lean condition and/or exhaust leakage. Is the bike completely stock? If not fill us in.
     
  3. Jack Klarich

    Jack Klarich Expert Member

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    What is the last thing done to your bike as in modifications to exhaust or air cleaner? Or have you changed plug brands or wires?
     
  4. dolt

    dolt Senior Member Contributor

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    Lot's of reasons for decal back firing; as requested more information will help diagnose the problem. The first thing to check is the exhaust flange nut; loose nuts will cause decel popping.:rofl

    If the exhaust flange nuts are tight then we have to look elsewhere.
     
  5. BUBBIE

    BUBBIE Well-Known Member

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    HD's Shut off the Fuel at harder than normal Decel..
    EXAMPLE:
    Say at fifty and at about 3000 RPM... Leaving OFF Fully the throttle is when it happens... No decelerate (fuel) firing occurs just a Smooth shutting down until about 1250 rpms is reached THEN you can feel it come back alive... (it's like turning Off the key but it is the Fuel shut off)

    IF you are Not leaving OFF the throttle completely OR interrupt this event, you may have popping from the exhaust.

    signed....BUBBIE
     
  6. dbmg

    dbmg Experienced Member

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    Depending of how hard the pop or backfire is, I can tell you my 2008 EG all stock is starting to some what back fire more as it ages on decel. The performance is not compromised at all. I believe that with 28,000 miles the mufflers are starting to burn out..... I do not consider it to be a problem otherwise....
     
  7. dolt

    dolt Senior Member Contributor

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    A properly tuned motor should not backfire on decel or any other time but, that's JMHO.:D
     
  8. thwart

    thwart Member

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    No mods at all. Bought the end of last year. Put on a tender and just getting some miles this summer. It didn't do it last year.

    It sounds like it's coming from behind me only when I downshift. So I assume exhaust.
     
  9. thwart

    thwart Member

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    It's just some light "popping" mixed in with a high revved engine. Maybe it's not even backfire? It's not that loud...
     
  10. dbmg

    dbmg Experienced Member

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    I would check exhaust attachments and forget about it....... Sounds normal to me.