I have a 1963 merc. 500. This week I ran without a problem until we had heavy rains. When the rain stopped so did my boat. It wouldn't start, it kept spitting fuel out of the exhaust and fouling out the plugs. When I cleaned the plugs it would start with the engine RPM's up. It would eventualy stall out and the plugs would be fouled out. What would cause this???????????? 