Ok I have a 99 YZF400 stock with a whitebrothers muffler the one with the baffels like a supertrap. I just adjusted the valves because it pops alot and they were way off not much clearance. That didnt help it runs great if Im crusing but I cant get it to idle yet and if you just grab the throttle it pops and snaps alot almost like a back fire. Im guna check the valve clearances again tomarrow but some direction might help. Thanks.