I have a gas boat. We had a shaft designed to mount weedeaters straight out of the box. No alteration cheap disposable power. You can usually find a neighbor getting rid of a weedeater and run it in alcohol or ether until it burns up. right now my boat has an echo 30cc in it, which are great power plants, even the lawn crews use them. I have done tuned pipes in the past and I think I would rather have to motors stock and have big cubic inches. Echo builds all the way up to a 50cc that will fit on my shaft. Here are the pics and movies of my boat.