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Major backfiring on deceleration


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Hi fellow riders! Thanks in advance for any tips or advice you may provide.
I have a '15 fj09 with a full two brothers s1r exhaust system and k&n air filter.
I also have the flash tune from two wheel dyno works from this forum.
About a thousand or so miles ago (am at 13500 now) I started to get some nasty sounding popping through the revs on decel. It seems to have gotten progressively worse over the past couple of weeks making it embarrassing to ride with how bad these backfires are, especially coming down the 6k-4k range.
I've got the tank off for my valve clearance check, because it's time. However I'm not inclined to think a misadjustef valve could cause this. (Please let me know if I have the wrong idea)
Do I need to get my ecu re-tuned? Is my air filter super dirty? (It's only got about 6k miles on it)
I've run fuel injector cleaner with little to no improvement.
Here's a kicker, I live at sea level and it runs like crap at home. I recently went on a trip to the local mountains and it seemed to be performing much better when I was about 5000 feet up.
Anyone experience these issues? Anyone have any ideas? Thanks again
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Two things will need to happen to get the popping: unburnt fuel gets into the exhaust and air must be getting in to allow detonation.
My Honda Dominator did this, shooting 4 foot flames out of the exhaust - then again, that was a carbed bike with no fuel shut off valve so par for the course, Great fun in unlit tunnels.
At 5000 ft, the density of the air is lower and the ECU will be sending less fuel anyway due to fewer oxygen molecules coming into the airbox. There will also be less oxygen getting into the exhaust.
So, check the seals on the replacement exhaust and check with Nels about the unburnt fuel getting into the exhaust. He should be able to tweak the settings to stop this.
This signature is left blank as the poster writes enough pretentious bollocks as it is.
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