I think we've hit upon something here -- my tank is vented through the filler cap itself -- you'll see the two small holes on the inside disc on the cap. During driving it works well, but for filling, there is no separate vent.
My filler is made up of basically 3 pieces -- (1) a flat round plate (~4.5") with the filler tube (~2" dia) welded to it, (2) a base piece which has the mount holes and the threaded ring, and (3) the filler cap assembly (the whole piece with the ring (inner threads), hinge, latch, cap, etc.
I'm thinking that perhaps I can re-make that round plate with the filler tube, but I'd also add another small hole with a vent tube, then route that to the vent on the tank (which is currently sealed off). I don't need to vent my tank since I'm EFI'ed (return-style fuel flow). Here's what I'm thinking...
Now, I've added a third drain tube that drains to the floor below the vehicle, in case of overflow during filling, but I'm thinking that if I orient the new vent tube towards the lowest part of that base plate, then I won't need a drain. And yes, I would make this with new metal so I don't have to weld on anything that has previously touched fuel.
Thoughts?
Cheers,
-Neil.