This is a 1986 engine. I bought it over the summer and it ran very well, plugs had been replaced and carbs rebuilt prior to my purchase. Today on the lake the motor will only run at about 50% throttle even though the hotfoot is wide open. Initially the motor shook when I tried to open it up, but this stopped rather quickly. It did open up and run one time, but the rest of the day would only get about 2500 RPM and seemed only to be at about 50% power or less. Thanks for any help you can provide.