Not exactly sure, but 4psi should be enough. I replaced the suction pump with a push pump near the tank, and it was only 8psi. The carb has a fuel return line, so excess pressure is only going to be used to push extra pressure back to the tank. The stock pump can suffer vapour-lock, and blockage at the filter and in the tank, and checking fuel flow obviously would be a good idea (while cranking the engine).
The pumps aren't commonly a problem, but the carbs often are. I'd get that carb cleaned out and make sure there are no blockages there. If the bowl is full of fuel, your pump is fine.