83 Evinrude Sixty horse. Started fine started to throttle up as we headed down the lake and heard a loud whack and motor jumped. No debris as if we had hit anything, to cracks in prop, no leakage. Fired motor back up and as we increased throttle it died. Same thing a second and third time. Then would not turn at all. Tried pull starting and very tough. Pulled spark plugs are clean, pulled plug on lower end and clean, compresion about 75 on each cylinder. Not sure what to think. Maybe bad gas??? fuel lines and carburator plugged??? or is it bad news???