i bought an 01 rm250 it had this setup stock pipe, with a pro circuit r304 shorty silencer, it ran good with that setup, but because i do all my riding at a state park i need a spark arrestor, so i bought a fmf turbine core 2 spark arrestor and installed it. first ride with the spark arrestor sputtering up top, great low to mid (i think) but no top. eventually fouled a plug, went to my carb went down on the main jet from 160 to 155 rode it again same altitude and settings and it rode a bit better, but still sputtering and still fouled the plug (longer ride duration though) im a beginner when it comes to jetting, what do you think i should do? i dont want to go leaner on the main for fear of running too lean what are some recommendations? setup: 01 rm250, 40:1 premix ratio, stock pipe with turbine core 2 spark arrestor i ride at carnegie OHV in northern california i think its about 100-600 feet above sea level. normally not humid at all.