Sorry to fool you on the title, But its a WR250F im questioning about. I know theirs alot of smart guys out their and am hoping to get some exposure on this to someone experianced. So please bear with me and read on....... The bike is a WR250F-2007 Its mods= Exhaust restrictor removed, air box snorkel removed, Boyseen accel pump and jetted accordingly(not by me but a professional) History= The bike has not been abused, ran mint when I bought it and for several tanks of gas and has been well maintained. The problem= One day out of the blue, it started to stumble on the topend like it was hitting the rev limiter when it was not. The bottom and mid ran and still runs mint(nearly 2 months later) The plug comes out sooty black. The first thing I did was change the plug, dump the gas and get new gas, check the choke to see if it was seating properly and checked for junk in the carb bowl. Still crap. I took it to the gut I bought it from(has a shop) and he tore apart the carb and started to re-jet it.(BTW their was no siginifant change in temp) I went to test ride it twice and the jetting changes did change the upper power band but not in a manner that fixed it. He ended up going so lean that he was several sized leaner than stock. When I test rode it, it did start to pull through the upper powerband but lacked its "hit" Definately not fixed, just masked. He could not find any other problems and relieved himself of working on it anymore. I then took it to another guy I know that only works on Motorcycles that is the best around I know of. He started by tearing apart the Carb and found nothing wrong, clean as a whistle. He agreed what was done earlier was not a fix but a mask of the real problem. He then went to the electrical. Tested the coil, T.P.S and everything he knew of. The end resault was that it needed a new CDI box. I ordered a CDI which is a elec- non-refundable/returnable part($197). Put it on tonight with a new clean air filter and...... no fix!!!!!!! W.T.F???????? I have no idea what to do next except the dealership which I doubt their smarter than this guy(Ive known him for 8 years+, he makes dealerships look like girlscouts) Last peice of info= Once again it runs mint on the bottom and mid. It is DEFENATELY not the carb. The plug is always black. When I twist the throttle up to 1/2 to 2/3 and hold it, it revs out smoothly and will go fast-70+mph. When Im going 1/2 to 2/3 throttle and suddenly twist it W.O. it studders, not bogs but studders. Any help guys? good, bad or ugly welcome! Thanks for any replies that may resault form this being posted in the wrong forum Jason.