hi all have pair of 454 350 gen 4 with around 500 hours, compression test 150 plus minus 2 on all cylinders, when i run the starboard engine all is good until it get to operating temp of 160 then a random knocking noise happens inside the engine. sortof like random marbles, this boat had sat for over a year and i had the tank flushed and gas replaced. higher revs create same result, random knocking. port engine is fine, both get gas from same tank. had electronic ignition install, knocking was same before and after. weird, any ideas. thanks fyi upon engine start and up to operating temp 160, sounds perfect, only knocks when at operating temp
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