i have a 1990 550 stand up and don't know what to do next. i am lost on fixing this thing . At first i would take it out and it would run for 40 min then not start agan.so i rebuilt the carb.But that was not it still did it.then i put new crank seals in it and it would not pump water so i put air in all lines not cloged.then i found the head gasket was blown so put a new one in still not pumping water . what do i look at next i am lost