Backfire on decelerating?

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Nov 2, 2020 | 10:28 AM

pomeara

Thread Starter

Cruiser

Joined: Jun 2010

Posts: 237

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From: St Louis

Backfire on decelerating?

2000 carbureted Fatboy is giving me some backfire noise on deceleration, particularly if I am going downhill and engine breaking. First time in 20 years I have had this issue. Took it into the shop and they replaced the exhaust and intake gaskets but no improvement.

Any advice would be appreciated. Thanks

Nov 2, 2020 | 10:47 AM

0maha

Seasoned HDF Member

Joined: Nov 2012

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From: Omaha

Decel pops are frequently associated with exhaust leaks. Did your shop carefully inspect the pipes for cracks? Even a very small one can cause this.

Nov 2, 2020 | 10:56 AM

MyFavRk

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Joined: Nov 2018

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From: Canada Flats

Exhaust baffles need to be repacked , perhaps your carb has gummed up and need a good cleaning , try running a couple tanks of sea foam through it , 1 once per gal .

How's the air cleaner ? A plugged / dirty air cleaner can cause a rich condition causing backfire . Intake leaks perhaps , bike at idle , spray some TB cleaner on them and see if the idle changes .

Clean the carbon out of the TB , tooth brush and some TB cleaner or sea foam will do , do the butterfly and seat as well .

Does your bike have stage 1 or just stock ?

How does it run / idle otherwise ?

Nov 2, 2020 | 12:52 PM

Bingee

Outstanding HDF Member

Joined: Dec 2008

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From: Ohio

Try increasing the idle fuel a little. If there's a lean condition on decel you'll get popping. A leaky head pipe will also cause popping.

Nov 2, 2020 | 01:33 PM

WP50

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Joined: Apr 2011

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From: W. Texas

Exhaust leak or lean condition is a common cause of a deceleration popping

WP

Nov 2, 2020 | 04:26 PM

pomeara

Thread Starter

Cruiser

Joined: Jun 2010

Posts: 237

Likes: 25

From: St Louis

Great feedback guys - thank you

Nov 5, 2020 | 08:06 AM

bustert

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Joined: Aug 2008

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popping is caused by accumulation of unburned fuel in the exhaust. normally with a correct working carb, the fuel is too lean to burn on a decel and exits the exhaust with no issue. in this situation, extra air from leaks does nothing. but for grins and giggles, we add in extra fuel, still to lean to burn in the chamber, it will accumulate in the exhaust till it reaches a point where it can ignite and cause the pop. so have you reset the idle mix? is the throttle stop too far open? have you checked float height?