OK, I have been working on this thing alone for the last two weeks and it is still not fixed. During my last ride my bike slowly developed what I think is a rich condition, burble and jerky at constant throttle, a black fouled spark plug, choking fumes, and poor idle. I need some help from you guys. 05' WR450 settings during last ride: Main jet: 168 Pilot Jet: 48 Fuel screw (turns out): ZipTy - 1.5 turns Needle model/Clip position: JD Red 5th clip Air box: Snorkel out, "punch-outs" removed Pipe: stock, plug removed The temperature is about the same as when I first jetted it and it was spot on then. What I have checked / changed: Pilot jet changed to 45 fuel screw completely closed but still a little rich. Valves- Exhaust: all within specification but on the tight side (around 20mm) Intake: one at 9mm all others in specification (around 10mm) Spark plug: was fouled but now new, this almost fixed the jerky condition. Air Filter: clean Carburetor: removed and thoroughly cleaned, all jets removed and cleaned and all passages blown out with compressed air. Has anyone had the jetting change so drastically that it required the fuel screw to be closed to run when the jets are within the recommended sizes? I am using fresh fuel, but could that be the cause? The humidity has been higher lately, how much of an impact does that have? Is there any circuit in the carb that that could be clogged that would cause it to be rich?