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problem child yz250f

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i am new to tt but i have a bike that made me turn to this site. to cut to the chase i have a 2005 yz250f that runs great until it gets hot. i have checked and swaped all electrical parts with known working ones and the timing is correct and valves w/in specs. it has a pro circuit gp low boy system and a pro circuit ported head, stock pisons and valves with hd valve springs. no ignition mods. the bike hits hard right off bottom all the way to wide open when it is warm. once it is hot the wide open responce cuts out on the main circuit. feels like i hit the rev limit although i am not. i think it is a lean condition but cant get this bike diled in. i run u4 gas but had the same effect with premium pump gas as well. i have swaped the head to eliminate that also. tried different exhaust, leek down tests, intake boot and air box are new. it is a FCR37mm stock carb and my settings are : 190main, 45 pilot, stock needle, stock clip position (4th from top) #60 leek jet, fscrew is 1-7/8 out. we are in dallas texas and this configuration used to make the bike one of the fastest around. still is until the motor gets hot. i have tried 195 and 200 mains and same thing, i have tried 185 and 180 mains and same thing. if you have any sugestions at all i would greatly appreciate it. thank you for your time

cody longmire



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