An air leak can cause the RPMs to spin up on the engine but before I looked at any of that Id address the other 2 possibilities in my earlier post first and rule those out as those are the 2 most likely culprits I can think of for a "run away"
I doubt theres anything wrong with the carb other...
I would read through THIS thread and use the nitro engine tuning flow chart after setting the LSN and HSN back to factory defaults.
The only things I can think of that would make it run away on you would be:
1) Loss of signal between the receiver and transmitter. There may be a damaged antenna...