Engine started to sound very loud and backfires at high RPM/under load. Took the head off and found carbon buildup in the intake valve chamber (could also see backflow from carburator when running rough). Cleaned & hand lapped both valves and set clearance. Doing an air pressure check when back together, seemed to be airtight. All back together and doing the same when running. What am I missing? I plan on doing air test again and relapping intake valve. Any wise words would be appreciated!
