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No air box lid

150 Views 6 Replies 2 Participants Last post by  Memosrt4
I have a 2012 yfz450 fmf power bomb header and big gun exhaust and it’s backfires A Lot on decel I am wondering if this could be from having no lid on the air box? Thanks
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It sounds like a jetting issue. Do you have the stock jets in your carb?
I’m running a 165 main 47.5 pilot and I have ordered a 170, 175, and 180 main jets to try out I also ordered a 50 pilot to see if it helps at all

with the jets I have in it now I turned the a/f screw out 4 turns (I know it’s a lot) just to see and it made a noticeable difference on the backfires
I take it you had the same issues as I do with the backfires?
It backed fire some but not too much. My main issue was that it wasn't running good at full throttle. I removed the air box lid and it stopped.
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