To begin with, make sure the engine's high-speed needle is as lean as possible without RPM drop or detonation when the engine's running at full throttle. DO NOT richen it from that point. If you're using a fuel with the proper amount of oil, trust the fuel. Most people tend to have problems with idle because they run the engine too rich. If the idle's too rich and you can't lean it more, then the high-speed needle's too rich!

That's the major cause of too-rich running at the low end. If you can get the high-speed needle set, you should not have problems with the idle. Please see our FAQ on pumped engines:

http://www.osengines.com/faq/faq-pumped.html