Hi John
To add to what the others have said, I once had a Morris Minor van that relied upon a pinhole in the petrol cap to vent the petrol tank. I changed the cap for one with a lock (during petrol rashoning) which had no vent and so as the tank emptied it created a vacuum until the pump could not suck the petrol through, and the engine stopped. Taking off the cap let in air, the engine started and off we went again for a few miles and then it stopped again.
It took me some time to realise what was happening, but once I had, and changed the cap for the correct one, all was OK.
Your story sounds very similar, so perhaps you may have suffered the same problem.
Chris T