Backfiring

[Logan43]

I just recently got a HMF Sport Series slip on for my 07 trx450r. It runs great but when i open it up it backfires very bad... Is this a problem or is it normal? What can i do to fix it if it is a problem??

[Mike/HMF]

Have you re jetted the carburetor to our specs? Air box lid on or off?

[Logan43]

When i bought it it had an fmf powercore 4 on it. It had been rejetted for the powercore 4 but im not exactly sure what jets are in it.. When i got my hmf i decided to try it with the jets that were in it and it ran great except for the backfiring which i wasnt sure if it was normal or not.

[Logan43]

I also have airbox lid on.

[Logan43]

It runs great and the throttle response is perfect but when I let off the throttle and decelerate it backfires like crazy

[Mike/HMF]

A little popping on decel is normal, but excessive popping on decel is typically caused by a lean low speed circuit in the carburetor. Try adjusting the fuel screw. --> http://hmfracing.com/forums/showthread.php?t=118 Also we start with a 48 pilot, and do yourself a favor and pitch that air box lid so that big thumper can breath!