I was going to keep out of this because everyone was doing fine until the business about what's supposed to happen if you run them 4 stroking rich came along. I've never believed the horror stories so when I bought a brand new ABC (very cheap off Ebaaaaaa ) I decided to find out what happens. I ran that engine absolutely horribly slobbering rich for 45 minutes. It still had the same pinch as it did when it came out of the box and when I stripped it completely for a very close look the only thing that was starting to run in was the conrod lower bush and the liner. The piston was virtually as new.

I prefer to find things out for myself rather than just repeat what others have read somewhere. So to counter the previous link on "How to run in" here's a link to my full description of that test, with photos.
http://www.rcuniverse.com/forum/m_28..._1/key_/tm.htm

I might add that, after doing all the testing, the best setting to begin running in a new ABn type engine seems to be at the point where the engine is breaking from a 4 stroke into a 2 stroke as others have already said here.