Could be a plugged fuel filter, or perhaps a clogged jet/passage in the carburetor. Also it's unlikely that this is a 2 cyl engine at only 3 hp. If it's spitting and gives a kind of 'wheeze' when it dies I'd look into cleaning and rebuilding the carb.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)