Take a look at 372039229177 just listed on E-Bay.
I'm scratching my head on this one. Is this something new or old? Sold in Australia only? Really from Horstman? Zoom in and you can see 1/92 on casting.
The clutches that I have like that one use Burco internals and a Burco drum for #35 chain. I don't know if Yamaha bought Burco parts or just copied them.
Mike, I think you've got it. Yesterday I decided to ask the seller (a kart shop in Australia). Here's the reply:
"This clutch was designed by Yamaha. A shoe type with variable engagement depending on the amount of oil added to the unit. I have a full users manual available.
Cheers, Allan"
He also sent an exploded view, and just like Mike said, it's a Burco or a clone. See attached.
Not a bad price, although remember to convert to Australian dollars and then include shipping. Unlike Mike's, these use 219 chain.