ok people, new to the 4-stroke world here! I just bought a 1999 yz400f and i love it...up until now, lol. Symptoms: High Idle, back firing (stock exhaust), stalling, when wot it boggs down (i need to gradually accelerate), smoking (may be from the sea foam i put in it... i never use that shit, I got talked into it) and top end noise, kind of like a spinning noise (it has hot cams in it from previous owner with less than an hour on them) I heard these engines are noisy so is the spinning sound normal? The guy I took it to said the carb is fine and may need a top end rebuild. The bike does not lack any power to my knowledge. I can get it to fire up first kick with the choke. Any ideas of what may be going wrong? Any help will be greatly appreciated! thanks!