So my customer brought in an 06yzf450. It acts like its running really lean. Backfiring, popping, shooting flames. With a minute or less its hot. I changed the gas. Changed the jetting. Adjusted the valves. Correct timming. Checked for an air leak. I can not figure it out. Nothing seemed to help. He does not want me to pull the head due to money. There is a rattle you can hear from time to time you can when kicking it over. So im sure its about to go. Any ideas or suggestions would be helpful.