late 80's 115 Merc inline six

[poliver82]

Help! I was out this morning crusing to my fishing spot on the St Lawrence and my motor lost power (like running out of gas) and shut down. Knowing I had gas checked the ball and it was still hard so started it back up and there was a knocking sound coming from the engine sounded like it was from the top. The motor had no signs of trouble before this occured. Anyone out there got any ideas what this could be I've heard it could be a valve or possibly a bad piston but wanted to see what the LOU crowd could give me for advice. any help will be grealty appriciated!! Thank You!!