I'm using the smaller summit electric that does not require the regulator and have a steady 8 PSI. I don't run a return line. I'm only running a Holley 750 though.

Did you check the vent yet? Leave the gas cap off and check the pressure again. Are you measuring pressure before or after the filter?

Kevin

what he said

Had the cap off and checked pressure before and after the filter.Its the same.I was playing with my old Holley pumps and it looks like the arm on the newer one is short like 1/16 inch than the old ones.I know the one I bought in 71 is shot for sure.The new arm dosent look worn.I wonder if it could be slightly bent?Ill have to pull the carter and see if the arm is as long.Rocky

you had the cap off in the same situation as you experienced the low pressure?
Or did you take the cap off a while after the situation?

Checked it with it on and off.Pressure was the same.Rocky

did you have the cap off at 50 mph?

No the cap was on doing 50.But If it was bad it would make a difference even idling.I believe the 65 used a non vented cap.Its been on since 65.Rocky

Could be the sock in the tank. Could also be a collapsed hose. I've even seen rags in a fuel tank blocking the pick up. You usually find something like that AFTER you've replaced the entire fuel system tho . You could put a tee in the suction hose at the pump and hook up a vacuum gauge. That would tell you if you have a restricted suction line.

I went through this last summer on my 440.
low fuel pressure, stalling, then starting right back up?
running like crap.
opening gas cap seemed to help.
replaced sending unit and fuel pump .
Turned out my fuel pump push rod was 1/2" short on one end/
replaced that rod and all seems find now.