My '90 rmx250 is running really rich right now, and fouling plugs after about an hour or so of running time (I'm at lower to mid throttle positions much of the time). The factory jetting for this bike (I have the stock mikuni tmx 38mm carb) is 420 main and 50 pilot. I have gone down to a 370 main (same pilot, planning to go down to a 45 though). Still way too rich. I have a fmf pipe and silencer, and boyesen rad valve. FMF's website says to use a 260 main with 45 pilot (for 0-1500' altitude and 50/50 mix of race gas and super unleaded @32:1). I realize this is just ballpark recommendations, but the 260 main sounds way, way leaner than the factory 420 main.. Does this sound weird? Or is it common to rejet this far from stock settings after adding a fmf exhaust system? I'm wondering if its safe to try going this lean, or if I should work my way down from my current jetting in gradual increments (this could get pricey though!).. Or is a better first step to go to a hotter heat range plug? I'm using a BR8ES currently. By the way, I'm at 2000' altitude, running a 32:1 mix with 91 octane premium gas.. Sorry this is so long, but I'd really appreciate any help from the jetting experts on here.