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Discussion Starter · #1 ·
After the mods to my R (jetkit, pro-design airfilter - open airbox - ct pipe) we put it on the dyno, good gains - 43hp -. I took it out yesterday for the first time and did a proper off-road test on it but one thing bothers me, it backfires very hard/load when you come of the throttle or gear down, what is the problem?
 

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did you adjust the air screw? I know with my hmf exhasut, i turned it out one full turn and it helped with the popping alot.
 

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Yup mine pops when decelerating. Its normal as long as you declerating while still in gear because the motor is still turning and is dumping unburned fuel into the exhaust and "POP" it combusts. If it backfires and pops while you are giving it gas then it is a lean backfire.
 

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Discussion Starter · #4 ·
We are at 3800ft, jet is 165 (if I remember correctly from the guy that did the dyno)
Climate: Winter now, 15 to 23 d/celcius.

We tested again today and after my mechanic(best in the world) tightened the bolds on the exhaust at the engine the backfiring went down by 90%, if I look at the replies to my first query it sounds about right now.

We had a stock Banshee also today but it was absolutely no competision to the 450r.

Thanks you guys.
 

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An exhaust leak will cause it every time.

What's happening is that the exhaust leak is allowing oxygen rich outside air into the exhaust path - this fresh oxygen allows the unburnt fuels to ignite inside the pipe, making the backfiring noise you hear.

This is the same concept that a smog pump works on in the automotive world- fresh air is pumped into the exhaust stream, which allows excess hydrocarbons to burn off before they're sent to the catalytic converter and out into the atmosphere.
 
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