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Hi,
The 72 gas tank, fuel supply and return, and gas vapor control system, were all designed to be used with a 'sealed' gas cap.
The affect of a 'vented' cap on those systems depends on if they're operating at this time.
Many people report a gas smell in the garage when a vented cap is used because the gas vapor control system is defeated.
Regards,
Alan
I have a vented cap on my '71 and the factory vent is blocked (don't have the charcoal canister).
I don't see any real problem if the charcoal canister is still present and hooked up, as the vented cap only opens when there's a pretty high pressure in the tank. When I remove the cap after driving there's a loud whoosh as air rushes out.
sealed cap was added to contain gas fumes thru the charcoal cannister.
adding a vented cap basically removes this capability.
and provides the possibility of gas fumes emitting from the car.
also if you neglect the cannistor and lines, they may eventual leak,
adding more gas fume escape paths.