Backfiring Through Exhaust

Discussion in 'Engine, Fuel and Exhaust' started by Hogfather, Apr 12, 2009.

  1. Hogfather

    Hogfather New Member

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    After complete engine warm-up the bike backfires through the exhaust when starting. Otherwise engine idles and performs very well. Any ideas on what would cause this?

    97 FLSTS Stock Engine
    45 Slow Jet
    185 Main Jet
     
  2. glider

    glider Veteran Member

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  3. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    Ditto above. Also, are you goosing the throttle when you shut the bike down? If so, try stopping that and see what happens. Also, are you seeing any fuel leaking while the bike is parked, even if just the smell of raw gasoline? Could suggest that your float needle is not shutting off the fuel right away. I suggest ALWAYS shutting off the tank valve (does your bike have the vacuum activated valve?).

    This sort of problem is associated with excess fuel in the cylinder that is on its exhaust stroke. Unless you have replaced the ignition system and changed to single fire, you are sparking the cylinder that is on its exhaust stroke too. So if there is excess fuel in the cylinder and the valves are open, you can get a backfire when the plug fires.

    TQ
     
  4. Hogfather

    Hogfather New Member

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    Thanks to all for the responses. Turns out the enrichener valve was bad. Replaced it this morning.

    Thanks Again!
     
  5. tbaker1212

    tbaker1212 Member

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    Sorry for jumping in here and I'll show a bit of ignorance. Mine does the same thing and I'm wondering if this could cause any damage?

    I'm new to the site and have to say that the info provided throughout is very helpful. Thanks.
    Thom
     
  6. glider

    glider Veteran Member

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    In excess, the backfiring can do damage to parts of the motor but in normal operation it is possible to get some after firing out the muffler with an incorrect mixture or exhaust leak.
     
  7. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    Hmm. Your bike is a different situation from the guy above, because I assume your bike is FI, right? I would be much more suspicious of an exhaust or intake leak. Check in the Self-help pages for techniques to check for leaks.

    TQ
     
  8. tbaker1212

    tbaker1212 Member

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    Thanks for the replies and referal to the self help area, I will check for an exhaust leak first. Thanks again.
    Thom