Perhaps if Dub Jett references "from the factory setting" the most critical part of breaking in (conrod bearings, etc.) has already been done. George Aldrich used to have break-in instructions on his web site. Similar to above: small prop, rich side of peak for the first two minutes, then it didn't matter as much. The idea was to heat up the cylinder for proper clearance as soon as possible to lessen the stress on the moving parts. After the first two minutes the conrod, crankpin, wristpin, etc. have pretty much seated.
Part of how you break it in depends on how you are going to run it in your plane. Some racers are VERY careful to not let it run very long in a four cycle. In CL stunt you run it much slower so you need to break it in richer.
Some ABC engines seem to keep getting better as the run-in during the first hour.
This is just opinion, individual results may vary [img]i/expressions/face-icon-small-smile.gif[/img]

George