1988 mercury 60 hp outboard sudden loss of power.

I have a 1988 mercury 60hp. While running at full speed I began hearing a long beep. Within 30 seconds I had a sudden loss of power, then died. It started right back up, but when I throttled up, it would only very slowly get to only 1/2 speed. When I got home, I pulled the plugs. The top plug had what looked like metal fragments. The other 2 looked fine. I then checked compression on all 3 cylinders, 135 on all 3, including the one with metal on the plug. So with good compression, even on the one with metal on the plug. What can the problem?