So you used the conventional one second from the top of the center column (with the cross on it) together with the mylar one at the bottom of the right column? Which one was in contact with the carburetor body? Remember that the flap valves can only work if they are right up against the flat metal carburetor body. If you put anything in between, such as the gasket or the mylar diaphragm, the flap valves can't work. So, the conventional item second from the top of the middle column needed to be directly in contact with the carburetor body, and the mylar diaphragm needed to be in between that item and the gasket, which would have been against the pumping chamber cover.
Have you replaced the fuel filter on the end of the pickup hose, inside the tank? If it is restricted by dirt it will reduce fuel pump performance.
