I have a yosh full exhaust with cherry bomb only, and I am not running lean. The head pipe will glow a little bit, but that is normal with any 450. It glowed like that the day I brought it home from the dealer, with air box lid on and baffle in. Just because the head pipe is glowing doesn't always mean that you are lean. If you are sitting still just reving the engine your head pipe is going to glow, I don't care how good of jetting or air fuel mixture is. Do a plug check. You can tell by the engine also if under power you are backfiring or missing you are probably lean. I have talked to yosh and a dealer and they said that it is fine with the cherry bomb. At my altitude, about 15 feet above sea level.