I'm not so sure it's from the carb, I think it maybe from the starter (part 131 on the diagram below), but it depends on the exact measurement & thickness, I can't tell from your picture if it is flat or not either.
Here are a couple of pictures of this part (listed as crankshaft thrust disk) which often falls out & is often missing too as a result, I did measure one earlier but have been distracted since & have forgotten, will check it again tomorrow.
David