I have a 96 5200 that all of a sudden started losing its prime when shut off. Once you prime it back it runs fine until you shut it off and it sits for a while. Thinking that a vent maybe stopped up because the fuel tank seems to be collapsing and sucks a lot of air in when the cap is taken off. Does anyone know if there is a vent or check valve somewhere in the line? I've looked and can't seem to find one. I replaced the fuel filter to no avail and checked all the fuel lines for leaks.