Alright, i have a 400ex and a 450r myself. My girlfriend has a 300 that is all stock accept i just bought a 11:1 compression piston last summer for it. And it had a moose racing air filter. Well im putting in a uni air filter for right now. Will i need to adjust the jetting for this? ALSO later im,thinking about a pro circuit slip on for it. Is that ok to just put on,without redoing the jetting as well? Im not to familiar with 300ex like i,am my 2 quads