[glenview289]

Check your vents. With a clogged vent, you will build a vacuum in the tank that the fuel pump cannot overcome. With a full tank this will not take long because of the low air volume. The test of running with the cap off or open for longer than 10 minutes will verify this condition. The small hole in the LeMans filler could be plugged and some bug could have crawled in the tank vent line itself.

Bill