1980 70hp mercury 3 cylinder. Starts easy,idles excellent, accelerates strong, smooth operation from idle thru high rpm. Problem: At high rpm above 3/4 throttle, motor has a rattle sound or ping/knock, back throttle to 2/3 range, noise stops. New plugs, fuel pump, water pump within the last year. Have not checked compression, (tomorrow). All help appreciated. Thanks.
