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backfiring through exhaust under deceleration

Engine, Fuel and Exhaust

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Old Jul 20th, 2008, 10:00 PM     #1
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backfiring through exhaust under deceleration

1997 Road King, stock engine, 2-into-1 DG exhaust, HD airbox kit, rejetted original carb, 24,000 miles on bike. Acceleration is good and recent fuel economy check on round trip to Rolling Thunder was 47+ mpg. While riding bike, exhaust backfires/pops when letting off of the throttle in any gear, very annoying not just to me but to other riders. Idle is ok, at about 900-1000. Tried adjusting the enrichener, but would only raise the idle and would not stop the backfiring/popping.
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Old Jul 20th, 2008, 10:04 PM     #2
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Re: backfiring through exhaust under deceleration

Depending on the baffles you have, it may be the problem, also check for header pipe gasket leaks and joint leaks too.
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Old Jul 20th, 2008, 10:05 PM     #3
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Re: backfiring through exhaust under deceleration

exhust leak
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Old Jul 20th, 2008, 10:23 PM     #4
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Re: backfiring through exhaust under deceleration

wow, that was quick! appreciate the fast response guys, I'll check it out tomorrow and advise of the results. thanks
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Old Jul 28th, 2008, 03:55 PM     #5
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Re: backfiring through exhaust under deceleration

Quote: Originally Posted by rk97hd View Post
1997 Road King, stock engine, 2-into-1 DG exhaust, HD airbox kit, rejetted original carb, 24,000 miles on bike. Acceleration is good and recent fuel economy check on round trip to Rolling Thunder was 47+ mpg. While riding bike, exhaust backfires/pops when letting off of the throttle in any gear, very annoying not just to me but to other riders. Idle is ok, at about 900-1000. Tried adjusting the enrichener, but would only raise the idle and would not stop the backfiring/popping.
My 03 rd.king did this after about 15,000 miles, shops said it was normal and I needed to change my riding habits. I own a repair shop and thought about what we do if it was a car, So evan though I was told a fuel filter never goes bad, I removed it and found it to be plugged, wow no more back fire and accelaration was better, Also check the harness to the ignition switch, mine was part way unplugged.
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Old Jul 28th, 2008, 04:14 PM     #6
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Re: backfiring through exhaust under deceleration

An occasional pop on decel can be heard even with the stock mufflers. The maps in these bikes cut the fuel on decel to a certain RPM and then reintroduce it again when the engine revs get lower. I have a feeling this is what is helping to get the pops.
Replacing the mufflers with aftermarket mufflers will accentuate the pops even more.
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Old Aug 8th, 2008, 12:55 AM     #7
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Re: backfiring through exhaust under deceleration

I would say to definitely torque your exhaust pipe nuts at the flange.

Mine had an increasingly bad popping and an occasional shotgun like bang on decel.
Turns out my aftermarket Cobra pipes had broke free of their pressed on chrome ring that the flange grabs hold of. After getting the pipes fixed I re-attached with new gaskets and the popping was gone.
For a while.
Unfortunately I used ANTI-SEIZE on the bolts.
NEVER DO THIS ON EXHAUST NUTS OR BOLTS!
The nuts stay tight for a very few miles and then loosen again and the popping returns. Seems the antiseize allows the nuts to vibrate loose very easily. I've tried blue locktite to solve the problem I've created. To no success.
Time to try locking nuts or lock washers!

Popping on decel?
Always assume it's the exhaust first.
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Old Aug 8th, 2008, 08:54 AM     #8
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Re: backfiring through exhaust under deceleration

Checking for intake leaks and exhaust leaks.

On the intake checking for leaks. Do I need to remove the air breather box completely? I can see the intake from the other side, but not the carb side.

On the exhaust leak. How do you check for that? On some bikes I owned, I would just listen for a hissing sorta sound or would blow smoke around the exhaust to see if it would show some sort of air movement.

Or is there a better way.
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Old Aug 8th, 2008, 12:24 PM     #9
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Re: backfiring through exhaust under deceleration

Intake, try it without removing the air cleaner, if nothing than you can remove it and check again in the areas that you couldn't access.

Exhaust, try covering the exhaust outlets (mufflers) with some heavy gloves on and listen for hissing at the head pipe.
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Old Aug 8th, 2008, 02:48 PM     #10
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Re: backfiring through exhaust under deceleration

This does not really apply to you directly, 97, but I found a crack in my rear pipe/cross-over just downsteam of the rear head at the split. The crack was about 1.5" and maybe 1/16" wide. Hard to find this without knowing it was there since it was hidden by the heat shield. So if you guys 'n dolls are seaching for the source of the popping symptoms, carefully check the headers beyond just at the port. BUT BE CAREFUL. Those pipes are VERY hot and just a momentary touch is at least a second degree!

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