Pat:
Thanks for the suggestion. That's was my initial thought, so I removed the check valves, soaked and blew them out in each direction. I checked for flow in one direction and checked that the valves closed in the other direction. Something I didn't mention was there was an audible high-frequency vibration on the rear bulkhead where the check valves are mounted. This is intermittment and they aren't even made by Lucas! My first thought was that the right check valve was not closing, allowing fuel from the left pump when only it was operating to flow under low pressure to the right tank, thus starving the carburetor. The question remains: Why does the right tank empty while no fuel is pumped from the left tank when both pumps are operating?
