What I was trying to say is, carburetors do not need 9psi, they will operate perfectly at 3lbs as long as the pump can supply the fuel volume needed (needs to be more than what's burned at WOT). Low pressure is not detrimental to a carburetor (IMHO anything above 5lbs is asking for trouble anyway). And keep in mind, with a mechanical pump volume will usually increase with rpm, as will static pressure (dead headed). While 3lbs at idle (600-800rpm) may seem low, it could well have 5lbs or more at 1500-2000rpm.
As long as the pump can keep ahead of the fuel demand (amount of fuel burned at WOT) and not reach pressures detrimental to the carb all will be good. However, starving the carb at WOT (lower flow rate than motor uses at WOT) is very detrimental to the motor.