Ok, this weekend I was in Homer returing to the dock, when one of my 115 started to act funny. It would now go past 27 rpm and then started to sputter/mis fire. I turned it off then back on and manage to get it up to 42 rpm but it still mis fired at 42rpm. I'm thinking it might be a spark plug. but at the same time when I put it in nutral the engine would shut off. This engine has 48 hours on it. Would a spark plug go bad this soon? It's a bran new boat and engine? If it's not the plug what else could it be?