My 1991 3.0 L mercruiser starts fine and runs great EXCEPT when I'm on the lake and I shut it down to let the kids swim for a while (maybe 30 or 40 minutes) it has a hard time restarting. I have to push the throttle foward and it will eventually start. It's been tuned up new wires plugs, rebuilt carb, everything but the fuel pump. That was tested with the fuel line disconnected and it fills a gallon jug very fast when the engine is turning over. Any ideas as to what the problem is? It gets a little scary.