Fuel Pressure for 1 Barrel Carb

Copied from All Ford Tech:

Yea, I know, it's not exactly Ford Muscle, but I'm trying to help the owner diagnose a problem from 150 miles away.

Searched for: 200, 1 Barrel, carb, 1v, 6 cyl...no luck
Application: 65 Mustang, 6 cyl - 200 CID, Auto trans, Points in the distributor, 1 Barrel Carb

The car wasn't running right...stalling off idle, difficulty starting when hot. So of to the mechanic it went. The car has had 5 carburetors in a row (yes, 5...five!) that are not working properly...leaking gas, and running pig rich. One of them came from a reputable outfit that does a LOT of advertising in the rags and on the web. Anyway, I don't think the mechanics have bothered to check the fuel pressure.
<font color="blue"> What's the maximum input pressure (from the fuel pump) that the needle valve can handle before the incoming fuel blows it off the seat?</font>

Thanks in advance for your knowledge of 4 barrel carbs, but that is not germane to this problem/situation.

Robert