I have a 05' YFZ 450 that has only about 20 hrs on it, just recently had its first service. Along with the service i put on a full yoshimura RS-7 exhaust , dyno jet kit, and a bmc air filter. I love the power it has but since then it backfires really bad when i get high rpms and let off, what can i do about this? Everone i know says that it is getting too much gas. So do i need to put a smaller main jet in it what else can be done. If anyone can help me out please do, thanks

 

If it backfires when you are off throttle/decelerating, you are most likely lean on the pilot and/or your fuel screw needs to be adjusted.

 

No poping is to LEAN jet up as scooter said another thing is look at the inside of the pipe is what my mechanic told me if its black is to rich but i have jetted down and i was running WAY lean but with some models thats a way to tell like on the 05's i beleive it is i go bye the noise it makes and by the dyno but i only use the dyno for lil mods to see what makes the big difference and what doesnt pull the big #'s i also use the dyno to get the jetting write

GOOD LUCK

 

Make sure you header pipe is bolted good to the head...If it is leaking any it will suck cold air up into the head couseing it to backfire..

 

ya mine does the same thing, i have been told it is getting too much gas but i havent had time to do anything