I am sure it has been covered but i cant seem to find it on my search. I have a 2004 crf250x. Right now the head is being rebuilt and I am putting it back togeather with some mods. Current set up is full R exhaust, cut air box, stock everything else...Main jet is 155 pilot is 42 and leak is 55...needle is in stock position. New set up will be addition of 2006 R cam, 2008 R piston...13.1 i believe is the compression ratio. I figured I would have to rejet for the new cam and figured that this more or less turns this motor into a 250R motor.....I know there are trans ratio differnces and newer 250rs have a larger bore carburator. I have been told that the 250 R and X head in 2004 were identicle...Mine is a California X so it has the smog pump port. I will also be disconnecting the Pink wire for the more aggressive ignition curve and higher rev limiter....I am running pump 91 octane fuel. I live at around 500 to 1000 foot altitude. I have been told that a 165 main should be good. I was wondering why the R forum has there mains in the 170 to 175 range?.....Also what clip should I move the needle too? Thanks ahead of time.