jetting

[sportrax stu]

hey guys im thinking bout jetting my 03 400ex. currently im running a powercore4 and a k&n air filter. i was just wondering whether it would be alright to run my stock muffler on it even if it's jetted. would this make a difference to the bike?
thanks

[shleprock]

i think you will be fine as far as problems, but an after market exaught will only make it run better Make sure you play around with the jet size if its runin to rich put a smaller jet in