2 different caps , both fit tight ,one won’t fit the other just a tad bigger. It may be a California only cap. One breathes better than the other. Never force it in cause it’s almost impossible to remove. It’s been awhile , I remember replacing the seal and changing something from old cap to new cap. After that the bike ran better at WOT , and using the deep well nut on the float bowl gave a very linear pull off of idle to WOT. For not having a bigger cam she really gets with it making power, might be my best jetting yet. I love Big singles.

If leaking due to rubber gasket buy some At205 reseal and put in a cup and let it soak for 24 hours, I did that bc of a leak and it rejuvenates the rubber no leak for 2 years also flip the arrow on fuel cap if it's leaking point up point it down see if that helps.

Aren't locking gas on bikes ridiculous anyway?
Who's gonna' steal gas from a 2 gallon tank?
Not to mention it would be easier to siphon from the fuel line

WTH, right?

I've also had it happen that I couldn't get the tank open with the key. I spent 10 hours trying to get the fuel cap off. I had to completely wreck the cap because no method worked. The paint only had minor damage, but perhaps it would have been faster to weld in a different model and re-fill and repaint the tank.

That was the reason why I was able to buy the motorcycle for 150 dollars. The previous owner had left the motorcycle sitting idle for 15 years for that reason. The gasoline inside smelled terrible and there was a black layer of tar on the inside of the tank.

When I had almost completely wrecked the tank cap, I saw that it was a very simple defect that can happen to anyone. I think I even posted it with photos. If it happens to you, there is nothing else to do but completely wreck the tank cap.

And it is build like a bunker.