Welcome to the (wonderful?) world of MZ's - they can be quite fun, if you have a running one - and it's not hard to get them running, really.
As for you carb problem - flooding after switching off sounds like a float issue to me. Do the bike feel a bit 'lumpy' when you ride, even when warmed up? Does it make much more blue smoke than you were expecting? If so, you're probably running rich and the carb is likely over-full.
...after your next short run, take the bowl off, remove the float and give it a shake. If it sloshes or rattles, that's your problem - replace it. Not sure if the Bings have plastic or brass, but if it's brass, just buy a new one. Trying to empty, clean and re-solder a 30-year-old-brass float yourself isn't worth the effort, trust me
While you've got the floatbowl off, remove the float needle and check the needle is still sharp - if you can push it up and still blow through the petrol intake, the needle might be distorted/worn. Less likely than a punctured float, but you never know.
You might also find this useful:
http://www.braigasen.com/bing_expl.htm___