Update for anyone who cares.
The problem turned out to be pure operator malfunction
. The selector valve does not work the way as I expected. If the selector valve is turned toward the the left side of the valve, then fuel
flows from the left inlet to the center outlet. If the valve is turned toward the right side of the valve, then the valve is shut off. If the valve is turned toward the center, outlet fitting, then fuel flows from the right side to the center outlet.
As a weird side benefit, I have now thoroughly traced, disconnected, re-connected and examined every fuel fitting in the entire system. And I have a nice little electric fuel pump
for future use in transferring fuel, priming lines, etc. <sigh>