My father recently bought an 800 watt 2 stroke generator for 50 quid brand new. OK, the voltage is wrong but for that money it hardly seems worth messing about, as said (if you just want to charge the battery). The output was dirty as hell, by the way, so don't anyone buy one of these to power anything sensitive! You'd need something to take this down to 12 volts, of course. I'd probabl;y have a look for a substantial 12 v switched mode DC supply, but that would cost you more then the generator unless it came out of a junk box somewhere.
If your plan is to run the outboard and / or charge the battery from the generator then you would be better off with a vehicle alternator IMHO. Have a look at your pulleys and guesstimate the ratio of drive to the alternator. I would take a guess that they need to run at around 5,000 - 10,000 RPM which might allow you to direct drive it from some 2 strokes. Alternatively a 4 stroke lawn mower engine typically runs at 3,000 RPM or so and would need gearing up a little.
They do need the "battery light" circuit wired up to a 12v supply via a bulb to provide a little current to "self-excite" the alternator at start-up.
Regarding power, let's say you got a 100 amp alternator. 100 amps output at 14.4 volts is just over 2hp. The alternator won't be 100% efficient, of course, but clearly a 3HP mower engine would be ample. 100 amps will charge the battery and run the outboard with output to spare!
Sounds like a fun project.
Kevin
very very nice
Raining and blowing a gale. Thankfully we have a nice pool and sauna and free broadband. 