Spitfire A different Spitfire gas cap question

[Trevor Triumph]

Driving the '64 Spitfire home from a weekend in Benson and Bisbee, Arizona the other week, we filled the gas tank in St. David. Several times after that the gas cap would open. Not a big problem, my wife or I could turn around a bit and push it closed. It's aggravating but at this time no damage done. It doesn't open once the fuel level is below three quarters of the tank. I'm wondering why the cap opens on its own.

 

[Mark Jones]

Sounds like your gas tank isn't venting properly.

 

[Andrew Mace]

I was thinking much the same thing, Mark. Is it the original cap? ISTR that 1970 and later Spitfire caps were nonvented caps, due to the evaporative emissions plumbing required by that time.

 

[BRSLimited]

My 70 has a non vented cap, emissions crap had been removed and vent line that used to go to the canister just goes under car now.