Fuel cap on or off shouldn't make a difference... you're tank will be vented elsewhere, and you are risking contamination of your fuel by doing leaving the cap off.
Sounds like an air infiltration issue to me... check all your connections and bleeders. Many fuel systems are under vacuum while running, so leaks don't show as a fuel drip, but air can get sucked in while running. When stopped, your air bubble works its way to a high point, then when started eventurally makes it to the injector pump and it quits....
Sounds like an air infiltration issue to me... check all your connections and bleeders. Many fuel systems are under vacuum while running, so leaks don't show as a fuel drip, but air can get sucked in while running. When stopped, your air bubble works its way to a high point, then when started eventurally makes it to the injector pump and it quits....