I just picked up a leftover 03 WR 450 last week and have a miss while riding at a constant speed. I was riding at 55-60 mph in top gear, with the throttle open enought to hold speed. Some times it runs fine other times it misses. If I get on or off the gas it runs fine. Pilot was changed to one size above stock at 1.5 turns out. Didnt like the glowing header I got with the stock pilot. I tried richer and leaner on the needle with no luck. Any suggestions?