That is the same initial issue I had. After a time it got to where it wouldn't even start. Turned out I had 2 problems, my voltage regulator / rectifier had shorted (when that happened it completely quit running) and the Power Pack. Once I unhooked the rectifier it would run, but back to the rough run anything over about quarter throttle. Have someone else drive the boat and tap the power pack with the handle of a screwdriver. When I did it to mine, each tap would do one of a couple things. It would either kill the engine completely, lose one cylinder or surge forward and run good for a few minutes.