If it is a JBA production(which I know them well), probably I was right.Some SK,JBA engines has wrong tapered LSN s.You can have great adjustment on ground but during take off it goes leanest to stop.This comes from inertia,unloading of prop etc.The solution is to cut a little of LSN tip or another way to provide LSN has better restriction as I described above.By the way,those engines are really great if you can do such a work.
Here is a fresh example.This is my Messerschmitt with a JBA 91 ringed.It needed a slight cut at the tip of LSN to prevent similiar symptoms as yours.
[youtube]http://www.youtube.com/watch?v=oWpTJPblnEw[/youtube]