For what it's worth: With the engine properly tuned and running perfectly on flat ground....... if you tilt the nose up the mixture leans out a bit, I suppose because the fuel has to flow up to the carb instead of straight/level to it. Err to the rich side, open your high speed needle a couple clicks and try it again. An over-rich mixture isn't near as dangerous as an overly lean mixture. You engine will run slightly rich in level flight and with the nose up will run just as it's supposed to. A lean mixture has always stalled my engine, a rich mixture will just leave a smoke trail for the most part.

My experience so far......