It sounds like it might have some muck in one of the jets.Try cleaning the jets,or cleaning the top of the carb with some carb cleaner.WATCH YOUR EYES,stings like mad.
If you can get it to rev,you could also try blocking of the top of the carb, to stop the air.Make sure it doesn`t get sucked into the carb.
This trick usually clears any muck that has got stuck.
Could be a fix until you find a replacement.