Fatboy backfires
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Road Warrior
Joined: Jun 2008
Posts: 1,381
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Fatboy backfires
My '08 will sometimes backfire when I start it up. It's a very loud pop and it runs ok, but stumbles slightly until warmed up. It has V&H Big Radius pipes, a fuelpack, and Screaming Eagle air. I scare them sometimes when I'm leaving work lol.
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,225
Likes: 11,348
From: San Diego, CA
Has it always done this, or has it started all of a sudden..... ? Have you done any work/mods/maintenance recently....?? Any codes....???
Just on this brief info, it could be an exhaust leak or intake leak... but if it has done it all along, most likely the tune...
Last edited by hattitude; Mar 17, 2023 at 04:08 PM.
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Road Warrior
Joined: Jun 2008
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Likes: 4
It's always been loud starting up, but for a few months it will pop like a rifle shot on occasion.
The fuelpack settings have been it it for years with the only change from V&H recommendations mainly to stop it from sounding like an air compressor when chopping the throttle. Someone posted how to do that years ago in here. I'll check for air leaks, hopefully that is the problem.
No work on it other than changing the plugs last year and no codes.
Big Al
The fuelpack settings have been it it for years with the only change from V&H recommendations mainly to stop it from sounding like an air compressor when chopping the throttle. Someone posted how to do that years ago in here. I'll check for air leaks, hopefully that is the problem.
No work on it other than changing the plugs last year and no codes.
Big Al
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,225
Likes: 11,348
From: San Diego, CA
It's always been loud starting up, but for a few months it will pop like a rifle shot on occasion.
The fuelpack settings have been it it for years with the only change from V&H recommendations mainly to stop it from sounding like an air compressor when chopping the throttle. Someone posted how to do that years ago in here. I'll check for air leaks, hopefully that is the problem.
No work on it other than changing the plugs last year and no codes.
Big Al
The fuelpack settings have been it it for years with the only change from V&H recommendations mainly to stop it from sounding like an air compressor when chopping the throttle. Someone posted how to do that years ago in here. I'll check for air leaks, hopefully that is the problem.
No work on it other than changing the plugs last year and no codes.
Big Al
I'm sure it's my fault, I can be quite literal, too much so, but I don't understand some of your terminology....
I'm not sure what "loud starting up" means... does that mean backfiring... does that mean high RPM....???
You adjusted the tune to stop it from "sounding like an air compressor when chopping the throttle"... Not sure what that means either....
My best suggestion would be...... If no air leaks are found..... And if this started shortly after making that adjustment for "air compressor" sounds..... then I suspect that adjustment is what is causing the back firing.... I'd undo that adjustment and see if the back firing stops....
Not sure what to say about "compressor noises" as I don't know what that means...
Sorry I can't be more help, my lack of understanding is my handicap...
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Road Warrior
Joined: Jun 2008
Posts: 1,381
Likes: 4
It sounds like a rifle shot. BAM! It echoes off the side of the building where I work and I have seen some of the women jump who are near the door.
Sounding like an air compressor was a common problem with the V&H tune. When you let off the throttle (chopping the throttle which means letting go back to the stop) it sounds like an air compressor running with the V&H tune. Someone in these forums figured out how to stop or make it less noticeable. It's a very old thread on here if it's still on here. Loud starting up is from the engine firing up and making the rifle sound. That is a backfire.
Sounding like an air compressor was a common problem with the V&H tune. When you let off the throttle (chopping the throttle which means letting go back to the stop) it sounds like an air compressor running with the V&H tune. Someone in these forums figured out how to stop or make it less noticeable. It's a very old thread on here if it's still on here. Loud starting up is from the engine firing up and making the rifle sound. That is a backfire.
I'm sure it's my fault, I can be quite literal, too much so, but I don't understand some of your terminology....
I'm not sure what "loud starting up" means... does that mean backfiring... does that mean high RPM....???
You adjusted the tune to stop it from "sounding like an air compressor when chopping the throttle"... Not sure what that means either....
My best suggestion would be...... If no air leaks are found..... And if this started shortly after making that adjustment for "air compressor" sounds..... then I suspect that adjustment is what is causing the back firing.... I'd undo that adjustment and see if the back firing stops....
Not sure what to say about "compressor noises" as I don't know what that means...
Sorry I can't be more help, my lack of understanding is my handicap...
I'm not sure what "loud starting up" means... does that mean backfiring... does that mean high RPM....???
You adjusted the tune to stop it from "sounding like an air compressor when chopping the throttle"... Not sure what that means either....
My best suggestion would be...... If no air leaks are found..... And if this started shortly after making that adjustment for "air compressor" sounds..... then I suspect that adjustment is what is causing the back firing.... I'd undo that adjustment and see if the back firing stops....
Not sure what to say about "compressor noises" as I don't know what that means...
Sorry I can't be more help, my lack of understanding is my handicap...
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Seasoned HDF Member
Joined: Sep 2008
Posts: 14,225
Likes: 11,348
From: San Diego, CA
It sounds like a rifle shot. BAM! It echoes off the side of the building where I work and I have seen some of the women jump who are near the door.
Sounding like an air compressor was a common problem with the V&H tune. When you let off the throttle (chopping the throttle which means letting go back to the stop) it sounds like an air compressor running with the V&H tune. Someone in these forums figured out how to stop or make it less noticeable. It's a very old thread on here if it's still on here. Loud starting up is from the engine firing up and making the rifle sound. That is a backfire.
Sounding like an air compressor was a common problem with the V&H tune. When you let off the throttle (chopping the throttle which means letting go back to the stop) it sounds like an air compressor running with the V&H tune. Someone in these forums figured out how to stop or make it less noticeable. It's a very old thread on here if it's still on here. Loud starting up is from the engine firing up and making the rifle sound. That is a backfire.
There will always be some unburnt fuel in the exhaust... That backfire can be caused by mechanical issues like exhaust leaks with a rich tune , carb/fuel injector leaks, etc.... Anything that will add air and/or excessive fuel to the exhaust.
I am still unsure what you mean by "air compressor" sound... I am going to guess you mean decel popping, which is often a lean condition in the decel portion of the tune.... The tune fix for that is usually to add 5% fuel, along with a 3° increase in timing in the decel portions of the tune map.
Just a guess based on your report, and if compressor noise is in fact decel popping, you may have an exhaust/intake manifold leak causing the decel popping. Then you adjusted your tune for the decel popping. By adding that fuel and not addressing the actual cause of the decel popping..... your tyne fix is now causing the backfiring....
I would check for air leaks around the exhaust and intake. If none are found, I would check the torque on exhaust gaskets, intake gaskets, and to any sensors on the intake and air cleaner. Then I would undo the tune fix for the decel popping to see if both the decel popping and now back firing are now gone...
Something worth checking... if that doesn't fix it, and you are confident there are no leaks... I would look into faulty/leaking injectors..
Good luck owth your diagnosis and repair...
Last edited by hattitude; Mar 19, 2023 at 12:20 PM.
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