I have read and read the posts here.. 2007 KX250F, it backfires moderately on deceleration only. Idles and revs fine, runs great, I have checked Timing, Valves, Filter, etc.. The jetting was at 40 Pilot and 182 Main. I switched to 42 Pilot and 180 Main... fuel screw is 2.5 turns out, I tried 2 turns out and set on 2.5 Still absolutely no change in the backfire behavior on deceleration.. so if I accelerate hard in 2nd and then let off abruptly it will back fire. Only does it in the upper rpm's. I have not checked the needle yet, but I assume its stock setting. Bike Runs great, I just assumed the backfiring could be jetted out of it. I have also put a new header gasket in, and checked the seal there & checked for any air leaks with wd40. Only thing I have not done is re-pack silencer, although this bike has a newer Leo Vince Exhaust. Which way should I go from here ?? Maybe I should of went a step richer on Main, Instead of Leaner. Everyone says these bikes are lean on pilot and too rich on main when stock ?? Backfire isn't hurting anything, but I would like to get rid of it.