i bought 08 YFZ450 and mine did the same plues when i would get on it it would bog out and die took it in to the shop they had it for 4 weeks tryed everything on it they rejetted it and couldnt find the problem so they started swapping parts found out my throddle sensor was bad they told me they rejetted it and they ajusted the Air/Mixture Screw havent had a red exhaust since then they told me it was to lean from the factory