Well It is suppose to only open and vacum suck the gas vapors when a gas pump nozzle enters the filler neck, You should hear a click when that happens, When there is no gas pump in the filler neck, No vacum should come from this hole... Reason for the tape is, In my case, when the gas pump is reomved from the filler neck, there is still a vacum coming from this vent hole.
In fact when i have my buddy give the throttle a nudge up to 3000 rpms, i can hear whining or howling from this vent. So that is a vacum leak which jacks up the a/f ratio, which makes the car run worse. I can always peal the tape back when pumping gas and reseal it once im done cause thats essentially how it was designed to work.
So somewhere along the lifetime of the car, the vent tube stopped closing itself once i pulled gas pump out of the filler neck
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