Fuel pressure issues
 

OK, help please!
have 79zx race car, fuel cell, high pressure fuel pump, aftermarket fuel pressure regulator. So at idle pressure is set around 42. Now when the throttle is opened, it's supposed to go up because of the vacuum to 50 psi., but it is not. If fact it droppes into the 30's and as the car accelerates, drops at the revs and speed increase.
I have pulled the vac line and the fuel pressure does in fact go up, so the regulator is working. I will replace the fuel filter today. I pulled my fuel line and put it into a gas can to make sure it was not the pick up and pressure was the same. Anyone have any ideas?

also, installed new fuel pump.

Aftermarket as in ebay? What's the brand?

Do you have to manually adjust it to go to 50psi?

I'd say it's not working if it's not meeting the target pressure.