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Hi all. I saw another thread about backfiring at idle. This is similar, but not exactly the same and I wanted to hear any advice. I've had this 2006 Vee for about a month or so now. I was stuck behind a slow mover the other day. She was doing about 20 in a 25. Normally I pass, but I just felt like chilling for a stretch so I upshifted and was running about 2500 RPMs, no load since it was flat ground. Just kind of idling along when the bike made one very pronounced backfire (loud cough) that, rather from the muffler end of things, sounded like it was into the airbox. Any ideas what that could be? It has a Power Commander under the seat but I don't know how to adjust it so have just left it alone.

Bob
 

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Mine does the same thing. It is a lean stumble. I have Two Brothers pipes and a power commander 5. My bike runs great but at around 2500 rpm with just enough throttle to keep it going not accelerating or decelerating I get the stumble / backfire through the airbox. Any more than the lightest throttle and it never happens. I was thinking of richening up the map there but I think I will leave it. Not enough of a backfire to blow off the throttle bodies, at least in my case.
 

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I was thinking of richening up the map there but I think I will leave it. Not enough of a backfire to blow off the throttle bodies said:
I really need to find a good tutorial on the Power Commander for technical dummies.
 

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I upshifted and was running about 2500 RPMs, no load since it was flat ground. Just kind of idling along when the bike made one very pronounced backfire (loud cough) that, rather from the muffler end of things, sounded like it was into the airbox.
now that you've had a pop or two inside the airbox, it's time to check and make sure that the air tubes didn't get blown off from the back pressure. Mine did. Man did it run ugly! Easiest way for me to tell the tubes were disconnected was to pull the tank and remove the air filter. Looking down into each throat I could see that the rubber gasket was off. (You might be able to see by looking under the tank but I couldn't get a good view of either one, so I pulled the tank.) I had to re-set each one and then tighten the clamp that held them on. I went gorilla-tight on the clamp just in case I ever had another airbox backfire. Fingers crossed, I haven't had one since.
 

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It has a Power Commander under the seat but I don't know how to adjust it so have just left it alone.
Power Commander for Dummies. https://itstillruns.com/adjust-power-commander-7512715.html

From the Power Commander site:
"Tuning Issues
Deceleration popping in the exhaust
Decel popping is caused by the detonation of unburned fuel in the exhaust pipe. This happens with high flow exhausts that allow more fresh air to be pulled into the pipe, causing the exhaust temperature to rise and detonate any unburnt fuel. Ways to reduce and possibly eliminate this popping are listed below and can vary between Harley-Davidson motorcycles and others. Exhaust leaks can cause decel pop, make sure the exhaust is sealed completely at the motor, and at any other connections.
Harley-Davidson: 1. For older Magnetti Marelli fuel injected bikes, adjusting the fuel table to remove fuel can help reduce popping. Highlight the zero percent column from 2,000 rpm to redline and enter in values from -40 to -50. Run the bike and see if the popping has reduced. Sometimes, the throttle position may not show zero at idle and should be correctly adjusted with the bike at full operating temperature to make sure it is reading zero.

2. On newer Delphi fuel injected bikes, we have found that adding fuel is needed to reduce popping. Highlight the zero percent column and instead of using negative numbers, try adding fuel to the map. Start with putting a value of 25 in the cells and see if the popping has reduced.

3. Adjusting the ignition table could also help in deceleration popping. Advance the timing in the zero percent column 3 to 5 degrees to see if popping has been reduced.
Metric and other: 1. Block off the fresh air injection systems. This will reduce the air being fed into the exhaust, causing the higher exhaust temperatures and detonation.

2. Adjustment to the fuel table in the zero percent fuel column from 2,000 rpm to redline, may also be needed to help reduce popping. A value of positive or negative 15-20 should be added and can reduce popping if it is still noticeable. Further adjustment may be needed, try increments of 10.

Do not do any changes below 2,000 rpm due to the fact that it could affect fueling at idle."
Power Commander Motorcycle Fuel Injection Tuning Module

This is "popping in the exhaust" rather than the airbox.
 
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