I have an older 5 hp sailboat kicker. It was completely rebuilt last year. It runs great out if the water but as soon as I put under load in the water it dies. I have tried adjusting the throttle and the fuel mixture a least 20 times and it will run fine for a while but as soon as I attempt to put in gear (at a lower idle) it dies. If I get it to to run it never runs at full throttle and seems to want to die, or does die, as soon as I slow the throttle down. We got it to run yesterday, went for a sail and after about one hour of sailing attempted to start it up , it ran for about 3-4 minutes and then died again. It would not start again untill I changed the spark plug for a fresh one. I have tried this a few times and a fresh plug works for a while then the whole process starts over again. Any ideas? Would a higher octane gas mix have any effect?