Can you check the coils on someone else 12v MZ maybe?
Otherwise, check and clean all the connections, also make sure the points close properly, and give the contact surfaces of the points a light rub with very fine wet and dry and clean, most ignition problems can be due to bad contact somewhere, sometimes it is the little alloy bridge to the condenser. Also make sure you have a good electrical EARTH to the engine, the ETZ’s engine are rubber mounted. Also maybe take the spark plug cap of and see if you get a spark by holding just the HT-wire to an earthing point with some pliers (faulty cap). Also You did not say if the bike was running when you got it, or was it a non runner?
I assume the battery is charged as well, I This is helpful.