OK, did you check the economizer linkage adjustment?
The best way to determine if indeed you have a fuel pump/supply issue it to connect a fuel pressure gage and clear hose from the fuel pump outlet to the carburetor. Keep in mind that low pressure readings could be due to an air leak, or restriction in the fuel inlet side. Did you try a different fuel tank?
I remember you mentioning that pumping the fuel bulb seemed to resolve the issue, which most likely indicates some sort of fuel delivery issue. But, a misadjusted economizer linkage or a bit of residue build up in the high speed jet might present similar symptoms…
