RE: o s 91 4-stroke
Mine likes to start fairly wet (with a good prime). If it ran prior to loosing the woodruff key and it isn't now and nothing was done to it inbetween then it sounds like glow plug or fuel.
I prime mine good and then with the glow plug ignitor connected, I turn over the prop (with a good hold on it so it doesn't pop on me) by hand until I get it to bump on the comp. stroke, then back it one turn and flip it backwards and it usually fires up. Sometimes it takes a bit of turning by hand to get it to bump.