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A hole like that also allows you to over fill the tank, leaving a greatly reduced air space.
Its so easy to fill the tank to a point where the tube just dips into fuel, if you leave it in the sun or even a cool garage it forces up the tube spilling over the tank.
Kev...where's your helmet??
Taking the evap crap off make the tank just like many many bikes I have had over the years. When the check valve, or the carbon canister plugs up, the bike will be dead in the water. I have never had a bike burn because of fuel leaking out of a vent tube.
I had a related problem with my California II tank, I'm sure the same style is used on many bikes of the era.If I filled it too full the air pressure would force fuel up the filler spout and it would run all over the tank.I can't think why they make this spout so long.I fixed it by drilling a tiny hole in the side of the filler spout, this lets it breath without gushing fuel.
The fuel doesn't expand, not very much at least, it's the trapped vapour that causes the problem.