i got a yfz450 06 model and it does good goin up thro tha throtal but when u let out of it it starts to back fire purdy bad!! its got a full LRD PRO 4 R EXHAUST SYSTEM, GYTR CDI BOX AND AIR FILTER. AND A GYTR JET KIT. any body know wt cld be tha problem thanks.

 

Wow dude. Not trying to be rude but that's hard to read.

Your lean on the idle. Screw in the idle screw all the way and back out 3 turns. Run and try again. If keeps doing it back out half a turn. Try again. If it keeps on try one more half turn. If it persists you'll should probably clean the carb a bit and make sure that idle jet is good and clean. You may have to go up a size on the pilot but, I wouldn't think so. Good luck with it.