[jmeckel]

I know this sounds like it will break the casting, however it does not...
Heat the casting around the jet to a DULL red with an oxy acetylene torch, preferably using a rose bud tip. Then using a welding gloved hand and a large pliers, dunk the carb into cool water. There will be a lot of hissing and popping, however the jets will be loose and easy to remove. On the broken ones use a easy-out if you can. I have rebuilt many, many carbs and always use heat and cool water, have never broke a carb casting and have never twisted off any jets.

The heat only to a dull red is very important, bright red and the brass jet will melt and you will have a bigger mess. DO NOT heat on the brass parts, they melt.