duden89 do you have the lid on your airbox? If you do take it off, if it goes away your main jet is to big. I had the same thing happen to me when I first got my 400 and thought it was the cdi bought a new one and made no change. Took the airlid off and it ran bad ass. Also check your valve lash.
Wossner 12.5:1 416 piston, Stage 2 hot cam, kibblewhite valves and springs, mild port job, billet clutch basket, Curtis Sparks ceramic coated exhaust, 1 down 1 up gearing, razr 2 fronts HD rears, powder coated (white) and gusseted frame, works tr front shocks, bunch of Pro Armor, ect. ect.