ballast resisters

For the fuel situation:
- Make sure the rubber line from the tank to the fuel line is not cracked, even a little bit. A small line crack can open up and let air in erratically; I had one that did it for over a year before it was found.
- Has the tank even been dropped and cleaned? It could have crud in it slowly blocking sock filter in the tank. This is common in these cars.
- If you are willing to repeat the test, try pumping out of a fuel container instead of the tank to rule the tank being clogged in or out.
- I would consider relocating the pump lower as a matter of good practice but not sure how necessary it may be. I have raced long endurance races with 2L 4-bangers successfully with electric pumps mounted a couple of feet above the tank with no issues ever. The old electric shuttle pumps used in small aircraft DID need to be below the tanks for priming, but that does not seem to apply as much for newer pumps; so it varies with the design. You don't seem to be having priming problems with your testing.