When exactly is fuel pressure regulator needed? I have a mechanical carter muscle car fuel pump with holley 750dp. At start up I had 9 psi for fuel pressure. That seems high to me. When it was running i didn't get chance to look what pressure was. I was too bust operating the throttle on the other side of the car.

 

Should be fine if it's not shooting out of the carb - the main needle and seat, controlled by the float, apparently have enough pressure to overcome the fuel!

 

Thats too high. Your Holley carb really want's 6psi MAX.

While it may run ok where it is now it would be better around 5.5.