Bought a 7mil cub 443cc from West Coast Atv, installed the motor in my frame and started it. Was running good, but at first rev a oring rubber parts got out of the exhaust. So took of the coolhead, changed the domes for 21cc 9 degree big bore domes and putted back the coolhead. Started it, noticed that this sound appear at the first start but realized that the flywheel came loose. Lapped it, torqued to spec and blue loctied it. Still the same sound but way less louder. Tried to change the kicker assembly, brand new kicker gear, tried another clutch basket, another waterpump and still does it. Squish is at 0.0045 each side. What could it be?