For what it is worth Don Goetz told me your vent size should be the same
size as your fuel feed, thus if you use 1/4 inch fuel line, use 1/4 inch
vent.  If 3/8ths then 3/8 vent.

You are supposed to check your fuel vents in your pre-flight check. aren't
you?

Bob Smiley
N94RK