You would then need to get the carb, and intake that came with the same engine. I would also make sure the camshafts are the same. Of course the timing curve also comes into play then too. Otherwise, as I said above, you could damage your engine.
You will gain power, with your moped, and lose fuel economy, especailly wakeboarding, with a loaded boat. With a car you can actually gain fuel economy by going to a 4 barrel. I have done it tons of times in automotive applications, but never in a boat. The big difference is boats are constant load, so damage happens faster, and mixture is more critical.
Your welcome