From what I can see the cap vents back down into an internal channel of the tank, presumably to the rear vent where the hose attaches. Did the pre-90's cap just vent to air at the top of the tank (and possibly vent fuel onto the rider)?Tanks changed in the early 90’s. Before then there was no vent on the rear of the tank, just the cap...... unless it was a California model then it had two vents. Otherwise no vents until early 90’s where it had one vent from then on..... again unless it was a California model in which it still and always have had two.
I found a gas tank that does not have vents. Is this common?
From the quick eyeballing of fuzzy ebay pictures I did yesterday, it looked like the spacing of the hinge bolts might be different for the two styles. Might not be a quick swap. Also might be a quick swap. Would be interested to see what illumination Doc can provide with his multiple bikes-worth of spare parts. >So, it would seem to me if you don't have a hole in the tank you could use the newer cap just by pulling out that rubber grommet and letting it the cap vent to the air.