On the green Koban (I doubt the green paint is correct) you can see the mixer known as the "Air-Flow" or "Air-Float" carburetor. Notice the finned cylinder heads, which were only used on 1914 models. For 1915, they changed to a domed cylinder head that did not have any lettering on it.
This style of mixer was more or less discontinued after 1915, and the mixer with the "KOBAN" cap was standard for the duration of the Koban production.
Probably safe to say that from what I’ve seen, one mixer needle fits all on Koban’s built with the "economy" carburetor.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...