WR 450 Backfiring

what causes backfiring on deceleration, too lean, too rich, or what....thx guys

LOL, both can. Too rich a needle/main can lead to excessive unburnt fuel accumulation in the exhaust. When the throttle is closed, the lean condition and heat can enabler this unburnt fuel to ignite - pow! The AIS on a WR tends to reduce the popping on a rich bike.

Also, if the pilot circuit is too lean (assuming the main and needle are spot on) this can also lead to excessive popping (the reason WR's have an ACV) Tweaking the fuel screw up to and no more than 1/2 turn can reduce it. You cannot eliminate it.

how about a looser header pipe......just looked and mine seems to be a bit loose which could be the cause of the problem and how can i fix this, i had the head ported and polished so maybe that is the root of my evil, is there any sort of muffler rap that i could use to snug it up a bit, thx for th info

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