What do you have in the shed? there are some engines you want to stay away from, for example the Poulan/Weedeater/Craftsman rear exhaust bottom carb reed valve units. While they have 4 transfer ports the carb location makes it impossible to tune when in a boat.

Piston port engines like Macculloch. Homelite, Stihl,Husqvarna etc are better.