Are you sure it is actually leaning out? I have an Evolution .45 that did the same thing but on the ground I found that it was actually getting too much fuel. What made me think it was too lean was that when it stopped in flight the fuel line was empty, but what was happening was that the fuel was just siphoning back into the tank before I got to the plane to look at it.

The engine still ran like crap though until this past weekend. I put a GMS muffler on it and it ran better than it ever had. It transitions beautifully now as well.

By the way, I have an Evolution .36 that as ran perfectly from day one, and a buddy got a .36 in which the head gasket wasn't but on correctly and leaked until he got new gaskets to install. The quality seems to be real hit and miss. Another flyer at our club has a .46 that has run fine from day one.