Now I think it's time to to major surgery. I reduced the spring to minimum but the engine dies on more than 1/4 throttle. Manipulating with Hi needle doesn't change a thing. So I started to play with Lo needle till I got full throttle rpm. The engine was running only on one needle (Lo end) almost full range so it is not the issue with fuel delivery to the metering chamber. And it looks like this carb size work good on this engine. As soon as I figure out the fuel problem.

Now I think that the Hi end just doesn't work. Maybe it is clogged or check valve doesn't work. Anyway this piece is going to have a major surgery. But before that I will try another body - maybe it will be better.

Of course any tips and comments are welcome.