theres 2 jets the MAIN & PILET. the pilet jet is for bottom end power changes and is fine tuned with the air fuel screw, the main jet is for mid and top end power changes a mid power change is done by the needle clip setting and a jetting change, and the top end power change is done with a main jet change and needle if needed. If u are running lean(to much air per gas) then jet up, and if u are running rich(to much gas per air) then jet down.
i hope this helps you.