Don't know what country you're in and what's available there, but here in the USA you can purchase carb cleaner in 1 gallon cans from car parts stores. You soak the carbs in it for an hour or so then rinse off with water and blow out all the passages with compressed air. That usually works well.
Nortonfan likes white vinegar. I haven't tried that (yet) but sounds like it might work well. Less toxic too.
Take a look at the "more amal problems" thread for more details...
Kleen-flo makes a good carb cleaner. I believe you should be able to buy it any from NAPA store (assuming you are in North America). It comes in 1 gallon cans and 2.5 gallon & 5 gallon pails. The pails can be used as dunk tanks. The 2.5 gallon pail is large enough to dunk a Norton head in.