read the jetting guide. read the needle chart. figure it out. no single "jet" is going to be perfect in your motor AND the motor right next to you. jet motors to what they want . the needle "range" is similar to the jet's "range". you need a differnt main for this and a differnt slow jet for that. needles are similar. usually i jet to the needle thats installed and if it doesnt like the mian choices i have OR the slow choices i have then the needle needs changed. most of the time the needle is a very fine tune adjstment IF the needle is in the close range to what the motor wants..