Problem with Austin Seven fuel supply

[Thowdfella]

Readers will be aware of all the problems I have had with my Big Seven but this one is common to others as well. My car regularly will not start or stops on a short run. Petrol can be seen leaking from the joint between the float chamber and the main body of the vertical downdraught Zenith vm30.
This means the carb is flooding and it would appear there are two possible causes.
1. Dirty fuel cut off valve
2. The fuel pump is not cuttin off pumping when the cut off valve operates.
I have three cut off valves - one new - and all three have been blown out and washed out so I strongly suspect it's the fuel pump. This is a new pump bought to replace the original and it does give a strong flow. However, I have just had the pump replaced with another new one and the same thing happened.
Has anyone else suffered this problem?

[Dave Prior]

Have you checked the float for leaks? Tiny pinholes can let in fuel, which obviously has an impact on how well the float...well....floats.
Put it in a bowl of water and see if air bubbles appear from anywhere.

[john williams]

The fuel pump pressure is controlled by the diaphragm return spring. Pressure should be checked by disconnecting the outlet pipe, connect the pressure gauge to pump outlet, and motor the engine on the starter. Pressure should not exceed 1.5 lbsf/inch. Do not operate the priming lever to test pressure, as sometimes the priming lever will pull the diaphragm down further than the camshaft operating lever.

[AustinWood]

It could be a worn float valve.

[Thowdfella]

The fuel pump pressure is controlled by the diaphragm return spring. Pressure should be checked by disconnecting the outlet pipe, connect the pressure gauge to pump outlet, and motor the engine on the starter. Pressure should not exceed 1.5 lbsf/inch. Do not operate the priming lever to test pressure, as sometimes the priming lever will pull the diaphragm down further than the camshaft operating lever.

Thanks for that John Will try to check but not sure where I,will find a pressure gauge to do it. 
To the previous reply, - there's no fuel in the float - it's OK.

[Thowdfella]

John. Your mention of 1.5lbs/sq inch pressure reminded me that the fuel cut off valve is marked 1.5 on its side. Is this related? And if so, can I get a higher rated one?