Then she went to the professional for clutch replacement and carburetors synchronization. In the meantime I found more parts on the web.
Fuel tank seems to be unstable. It is mounted on four screws but still it feels like something is not right. There are two rubber spacers underneath the rear mounting plate... I mean they should be there :-) One of them was missing.
All right, now is better
Missing ram-air seal on the place
Just in case to avoid future problems, accelerator wires were replaced too