HD description is incorrect, float chamber is on the side like HS. The thing underneath is the diaphragm chamber. https://sucarb.co.uk/technical-hd-type-carburetter-diaphragm-jet-and-auxiliary-enrichment > I did some poking around, and found this link which is kind of fun > http://classicmini.weebly.com/how-do-identify-my-carb.html > >