if you run a higher ethanol content than 10%, you'll need to rejet ( richer ) the carb accordingly.. so if the boat was running 20-30%, and wasn't tuned for it.. that was the problem.... as far as lead in todays gasoline.. not as much as a trace of lead anymore.. lead did not provide lubrication. it provided a 'cushion' for the valve seats ( this is b4 hardened valve seats ).. and even with the new gas in the old engines, it's not a problem.. they will overtime get valve ressession, but there never run hard enough for it to happen quick.. most of the engine work I do, is on engines from pre 1970, because I deal mostly in classic cars