Early vs. Late dusters

I actually added one to my Duster because I got sick of my garage filling up with gas fumes every time I'd park after a drive. That was when I had a Carter AFB though, my "new" Street Demon doesn't have a bowl vent fitting for charcoal canister so it's now removed. Pretty sure I saved it though.
Why not just plug the vent? I've never heard of anyone else having this problem