Is the noise from the intake or the exhaust? Either way, it's probably caused by a sticky or burned valve. Check and correct the valve adjustment, then do a compression test. If one or more cylinders checks low, do a leakdown test where air pressure in applied through a spark plug hole with the crankshaft locked, and listen for a leak at the carburetor, tailpipe, and oil filler to see where the pressure is escaping. You're probably headed for a valve job to solve the problem.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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