Diagnosing a Potential Fuel Problem

First things first. What type of ignition are you running? Do you have it wired through a ballast resistor? What do you have your initial and total timing set at? How much voltage is going to your coil when cranking? You should have full voltage at the coil while cranking the motor, 12V+.

Have you checked for vacuum leaks and confirmed that you have absolutely none going on?

Holley needle and seats are pretty hit and miss. On average they work pretty well, but if you get 10 sets, there will be about 2-3 pairs that will control fuel pressure much better than the rest, sometimes in excess of 11 psi and some can barely control 6 psi.

Confirm you are running a deadhead regulator. Where do you have your float levels adjusted to? How is your fuel system plumbed? Is the pump above the fuel tank? Do you have a fuel filter before the fuel pump? How long does the fuel system take take to fill up a gallon container? Is your fuel tank vented? Has the choke system been removed from the car?