When you strip down the carb pay close attention to the jets and orifices. On the small engines I believe there's an orifice hidden under what looks like a rubber plug. Any crud in these and you're pretty well toast.
They are easy to miss.
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)