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Backfiring Through Exhaust

Engine, Fuel and Exhaust

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Old Apr 12th, 2009, 04:37 PM     #1
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Backfiring Through Exhaust

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
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Old Apr 12th, 2009, 05:03 PM     #2
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Re: Backfiring Through Exhaust

Possibly an exhaust leak.

Exhaust Leaks - Harley Davidson Community

Muffler Leaks - Harley Davidson Community (Muffler Leaks)
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Old Apr 13th, 2009, 11:54 AM     #3
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Re: Backfiring Through Exhaust

Quote: Originally Posted by Hogfather View Post
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
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
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Old Apr 13th, 2009, 03:38 PM     #4
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Re: Backfiring Through Exhaust

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

Thanks Again!
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Old Apr 14th, 2009, 08:03 AM     #5
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Re: Backfiring Through Exhaust

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
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Old Apr 14th, 2009, 08:05 AM     #6
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Re: Backfiring Through Exhaust

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.
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Old Apr 14th, 2009, 11:35 PM     #7
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Re: Backfiring Through Exhaust

Quote: Originally Posted by tbaker1212 View Post
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
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
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Old Apr 15th, 2009, 07:06 AM     #8
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Re: Backfiring Through Exhaust

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