Heat Cycle the engine for the 20min break-in. Do not be shy about leaning it a little, just keep it on the rich side but also lean enough for the engine to get to operating temps during break-in without dyring from either bring way to rich or lean. It's a balancing act, but the heat-cycling procedure will pay off.
Check out thes thread:
http://www.rcuniverse.com/forum/m_55...mpage_5/tm.htm
It should be made a sticky and it should als be made into a "sticky search" so it is the only threat that appears in the search engine under the parameters "break in." No one wants to read the other hundreds of other usesless threads that DO NOT even describe the break-in process.