03 WR450, hard to start. Won`t idle unless I have the choke part way on. I have pulled the carb and cleaned it. Flames out the exhaust when it backfires. The bike did the same thing with the stock exhaust on it just not as bad. I just put a FMF pbomb header and powercore sa on it. Header turns cherry red when at idle for about1-2 minutes. I`m beginning to think I should have bought a YZ250 2smoker! I`m going to give this thing 1 more chance with some jetting if that doesn`t work out the first $3100 (without the FMF) will take this thing out of my garage!