my 250r will run right with the 150 main jet it has no power and cuts out i just had it bord and it is piped but it will not run right with a 150 main jet i went down to a 140 and still not right but better i do not want to go down to much because i do not want to run it to lean because when i got it it had a 115 in it and it ran beutiful but i think that it to small what do you guys think o ya it has a 50 slow jet the air screw is 1 and 1/2 tuns out and the needle clip is on the 3rd slot thanks for any help nick

 

a 140 jet is still fat i know with the 300 kits you use only a 135 jet. on my 84 250r im running a 130main jet an i have an aftermarket silenser an run no air box lid. an it seems to run pretty good

 

jet untill it runs the best then go up one jet size larger. then do a plug chop. see what she looks like. this is exactly how i do it and many others. forget about the pilot "slow jet" get you main jet rite "good power and a healthy plug color" then mess with the clip. try to keep your clip a little rich the bike runs in the needel zone most of the time.

and it is good to be a little fat in the middle when coming off of a hard full throtel run.