What would affect the flow from the fuel distributor ports if you have no restriction in the outlets? The way you have it rigged, pressure will be nil in the plastic tubes, and the differential pressure valves likely can't regulate that. The fuel distributor is not designed to shut down fuel flow, but to regulate the pressure at low flow rates - and just below the 40-50 psi of the injector check valve is as low as it needs function.
If you connect the injectors, you should be able to build back-pressure, and maybe trapped air will be purged from the unit.
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7