jetting?

[2001300exguy]

i have a mostly stock 2001 300ex all i have is a drilled out header
and sometimes run with out the airbox lid. im going to be getting a yoshimura comp series slip on and dont know what size to jet it
if anyone could help thad be nice.

[cals400ex]

i can't tell you exactly what size jet to run on a 300ex, but taking off the air box lid will change jetting. you need to either set it up for the air box lid on or off. i would say with the air box lid off and the pipe, try a keihin 132 mainjet. with the air box lid on, try a keihin 128 main jet.