Pressure building in tank

If that's a metal fuel line I see in the pick you might be boiling the fuel in the engine compartment (fuel line) when it get too hot. You could wrap it with header wrap like I did or slide Silicone tubing over it?? I would think that pressure in the tank would help push gas to the engine?? Now vacuum in the tank might keep gas from getting out.

On the other hand, if it's building pressure it means that it doesn't have a vent which means that eventually you could pull a vacuum on the tank restricting fuel flow. Maybe your hearing the tank sucking air when you remove the gas cap???

treblig