You should normally set the engine about 800 rpm down from peak prior to launch.

If it run ok on the ground and then STILL goes lean after launch, check the fuel system. You are very likely getting fuel foam. As the engine unloads in the air, it is hitting a note that is foaming the fuel.

Balance the prop

Make sure all of the fuel lines (including the tank clunk line) are intact and have no holes

Make sure the fuel tank is 100% wrapped in foam (can not touch anywhere on the airframe)
- or - switch to a bubble-free fuel tank