Process of elimination. Skip the lift pump and run directly from you're guaranteed fuel source - gatorade bottle - to electric fuel pump to secondary filter. If it still dies, then look real closely at your secondary filter ass'y. If you are 100% sure that is not the source of the air leak, well, the only other possibilty is a problem upstream. IP/timing.

Conversely, if it runs fine, you know the problem probably lies downstream. A bad lift/primer pump, a rusty fuel line, a clogged tank strainer, no fuel in the tank....

When you get it started, does it run "well" for a bit, then die, or is it struggling the whole time?

Jay.

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On the road, currently:
'83 300D (German spec.) 168k mi. - - Wolfgang (tucked snugly away for the winter!)
'87 300D 375k mi. - finally went over to "The Dark Side"
'87 300TD 225k mi.
Cannondale 66cm CAAD5 w/Campy/Jamis Aurora
Hujsak Custom Fixie/Landshark Track Shark Custom/Ahearne Custom 29'er