Quick response:
1. Iron, lapped piston - run slobbering rich, 4-5 minutes at a time or longer. Continue to progress gradually with slightly leaner settings, until it can hold a steady 2 cycle. Just a guess, but probably 5-6 tanks (at 5 min. ea) is a good range to increase from slobbering rich to a slight, breaking 2 cycle. Make sure the engine completely cools between runs. Get to the point where you can lean it out without sagging - any time it sags, immediately richen up the setting. When you can lean it out with no ill effects, and it's about to pull off the test stand, it's time to put it in a plane. For a bushing engine (no ball bearings), double the tanks and runs suggested above.
2. ABC or other special, non-ferrous acronym - short runs of 2 minutes a piece. Never run it in a slobbering rich condition. A rich setting - breaking back and forth into a 2 cycle - is as rich as you should get. Again, make sure the engine completely cools between runs. A good, modern engine may take only 3 or 4 runs at this rate. However, you always take a risk that you'll get stuck into a lean run in the middle of a flight with no control. Therefore, continue to be cautious until you have a dozen flights or so.
Other points:
- Foxes always like Castor Oil, whether they're bushing, BB, or whatever. Personally, I would never run a Fox with less than 20% oil.
- FAI fuel has no nitro. If you don't use nitro during break-in, then the engine may not be broken in for higher speeds and temperatures if you use nitro later.
This works for me, unless it's a Fox 35 - then use at least 25% oil, and mulitply the times in #1 by four or more.