I run mine at a few turns out 2~2.5 . From day one my 39 idled very well. Are you certain you don't have a pinched fuel or air line making it difficult for the engine to draw fuel. I also completely disassembled the carb on mine and blew it all out before it ever saw fuel, could be some factory debris in there.

When it starts at half throttle is it running rich, lean, both, is it consistently doing the same thing ???