I had a couple fuel leaks around the fuel pressure regulator, got them fixed and before I installed the plenum and runners I checked the system for leaks. I got 42 psi and it held for 30 minutes with no leaks. After I installed everything and got it started it immediately flooded and wouldn't run.

I pinched the pressure line and the pressure bled down to 0. I pinched the return line and the pressure went over 100 and didn't bleed down. I assumed from that my regulator is bad.

I have a ,72 Vega with an in tank pump. I kept that pump operationale and use it to feed an external high pressure pump for the TPI. I disconnected the TPI pump and it started and ran on the low pressure in tank pump ( no more than 6lbs and couldn't get it to register on the fuel pressure guage). Mind you it didn't have any throttle response and ran very poorly but it ran. It would not idle. My injectors are brand new.

I'm puzzled as to why it held good pressure after fixing the leaks (O-rings) but will not do so now.

Does this sound like a bad regulator or something else?