Air in fuel lines indicates that there is a leak somewhere before [ upstream of ] the fuel supply pump. This is called the "suction side " of the pump. [ If the leak was downstream of the pump, fuel would leak out - this is called the " pressure side " ]
Check the system this way, starting at the fuel tank - >P> Remove the fuel standpipe [ pickup tube ] by unscrewing it from the tank. This pipe extends into the tank, so it will always be submerged in fuel. Inspect it closely for cracks, particularily at the weld. You can also cover one end, & blow into the other end, while wiggling the pipe, to check. If a screen is found on the end, remove it & throw it away.

If this pipe cracks, it will allow air into the system as soon as the fuel level in the tank is low enough to expose the crack to air.

Next check all fuel hoses for condition, by bending a section into a tight radius. If any small cracks are found, replace all hoses & clamps that lead to the fuel pump. Use ONLY USCG approved fuel hose, not automotive grade. DO NOT overtighten the band clamps. Better yet, install the type that does not have perferations through the band. These will not cut the hose when tightened. Also ensure that all threaded fittings are tight. It only takes a pinhole to allow air into the system.

Now check the O rings on the Racor fuel filter cover for condition & correct installation. These should always be replaced when changing the filter. If you don't have a primary filter, install one, to protect that exspensive engine.

If the fuel pump uses banjo bolts for fuel connections on the suction side, [ this is a hollow cap screw through which fuel passes ] change the copper gaskets . DON'T overtighten them, or you have created a leak.

It's also possible that the pump diaphragm has a pinhole - check it by substitution.

Now bleed the system & run the engine. If air is accumulating in the Racor, [ check by removing the cover, the filter should be full to the very top ] the leak is somewhere upstream from here.

Are you sure the engine stops because of an air leak? Maybe it stops because the tank vent is blocked, creating vacuum in the tank as the engine is run, that the pump eventually cannot overcome.

Joe DeMers