Ivy: Tank Vacuum, or Obvious in Retrospect

Went down for another session to revisit the engine issue.  When I twisted the gas cap off, I heard the distinct hissing sound of air rushing in.

So it was a vacuum issue in the tank.  Now all the symptoms added up - the engine dying after a short period, but then running after resting a bit.

I had removed the extra DIY gaskets from the cap because they looked ragged.  Could some debris have found their way into the vent hole.  Where is the vent hole anyway?

I tried loosening the cap a bit and went for another ride around the block, but same thing happened.

Finally, just switched the cap with Roxy's to test - and she ran perfectly.  So it's definitely the cap.  Just need to figure out where that vent is and then clear it.


Also checked the odo against a phone app and found it was dead on!!  Seemed accurate down to 0.01 mile.