Where in this thread did you read to run the engine lean?

This is a direct quote from Clarence Lee, taken from the June 2002 RC Modeler, page 40 column 3.

Gee Bruce, someone who actually reads the instructions. That's a rarity. As my friend Dave Gierke who authored the engine break-in article you mention said, it is not a good idea to run an ABC or ABN engine in a rich 4-cycle. As we have explained quite a few times in previous columns, the ABC and ABN pistons are fit tight at the top to allow for differential expansion rates between the piston and sleeve. At operating temperature the proper running fit is achieved. If the engine is run overly rich it does not come up to operating temperature and the fit remains tight. This more or less results in the piston being jammed up and yanked down, stressing the rod and wrist pin, especially when the engine is misfiring and running ragged in a 4-cycle. This, in turn, can lead to a broken rod or wrist pin.