ORIGINAL: Rodney
Highly doubt that rust is your problem, more likely congealed castor oil residue. Solution:heat. Heat the carb and engine with a high intensity heat gun or torch while gently applying pressure to the moving parts and they will soon start moving.
This would be a last resort kind of thing for me, if the problem is oil residue there are plenty of cleaners that can be used that won't risk damaging anything. If the cleaners don't work then I would try to do what you said.