i also have a 08 yz250f , right off the back i got the carb rejetted,boysen quickshot, fmf 4.1 and mega bomb, SUSPENSION , and some cr high twinwalls ,a uni filter , i also have some big feet for a 15 year old (size 12) so i baught some wider, sharper pegs, and a extended shifter . after doing that , my bike was race ready .
u can call al posey to find out the jetting specs .