do you have a lift pump

would be good if you explained how you have it all set up

those pumps dont suck well, need to be well primed and a lift pump helps if the holley is mounted above the tank

should solid stream of fuel at least half a meter from my experience with them (detatching the hose at the carby and turning the pump on)

other thing that can happen is if the tank isn't breathing properly it can get pressurised (or become a vacuum) restricting fuel flow