[Jac Mac]

1. Call your builder.
2. Gallery plugs at front or at single rear plug high up in valley.
3. Pickup tube/screen fell/broke off pump.
4. Relief valve in pump stuck open.
5. Cover plate on pump loose.

Those are the obvious ones that 'can' happen, you can remove the fuel pump to observe while you hand prime with an old dist shaft to check if its the front gallery plugs, if you cannot get a continous flow while priming by hand then its likely the pump/pickup scenario, if you get flow & its not at front then remove intake to check that rear plug & or lifters.