Having gone through a similar experience earlier this year, I concluded a healthy N/S should be able to hold 8 or 9 psi. Following a method shared by Cliff, I actually measured mine and it held 12 psi before being overwhelmed. Yours could be different (N/S dia, float, float fulcrum, etc.) but that's what I found. Mine is a 69 Buick carb with a slightly larger-than-stock N/S dia and one of Cliff's nitrophyl floats.
There are lots of reports of aftermarket mechanical pumps supplying pressure over the "preferred" 5 or 6 psi but I wouldn't immediately assume 8 or 9 psi is a problem.
I recommend you start by rebuilding the carb with one of Cliff's kits. While you're doing this, look for dirt. I found rust particles inside my carb, ended up replacing the tank. The source of my rust was the sending unit in the tank. I also found rubber particles from a degraded hose. These all got replaced with the tank.