In pumping the fuel primer bulb constantly, you're acting as a manual fuel pump. Diagnose being.......
1 - You have one hellava leak between the fuel pump and the fuel supply resulting in the pump drawing air... BUT... if this was the case, by the same token, you would have one helava fuel leakage at that point.
2 - The fuel pump, whether it has been converted back to a regular fuel pump... OR... if you're still using a VRO, whichever the case might be... the pump has failed.
3 - The operational hose leading from the fuel pump/VRO to the crankcase has split, broke, cracked, whatever. If so, there should be a rather loud noise coming from that hose area.
4 - The related piston that provides the vacuum/pressure to operate the fuel pump/VRO has blown.
I'd suspect a failed fuel pump/VRO.