I don't think that carb had a diaphragm. Has the typical needle & seat, float and jets but the petcock is actually the fuel pump I guess you could call it. There is a huge spring under the top of the carb with a rubber disc that rises as the throttle is opened plus a vacuum device on the side that has something to do with the throttle. Not a whole lot to them.
http://49ccscoot.proboards.com/threa...ctions-diagram