i have a 1987 force 125 outboard. when i try to get high speed it takes off verry good once it gets to 28 mph it slows down to 20 then goes on again than slows down, all by it self. i was checking yesterday and i saw that even on nutrual the rpm goes up and down like 1000-1200. it moves the whole time. so does eny one know what might be the problem? and why dont i get more than 28 mph? the boat is 1987 bayliner cuddy cabbin.