Hi, I am new to this site and need some help. I just put a new piston+ rings and adjusted the valves on a 426. I got it all back to gether and it seems real lean on the bottom end, lots of poping out the muffler at idle and up to quarter throttle. The header pipe also gets CHERRY RED if bike idles for one minute. Is this a common problem on the yamahas? What is the likely problem? ] Please help this is not my bike I am doing this for a friend.