Thanks again, Timp.
Those mikunis are really bizarre in trials, but work very well in other applications. The mixture screw is located in the rear, with vertical orientation, I suppose? I'm really dangerous fiddling with sensible parts, but can't resist! A search in TC forums has revealed that Betas 4T of previous years came with lean jetting to overcome homologation. Maybe yours also, and Lampkins fixed it in PDI before send your bike.
I would pleased to ring Lampkins, but I live in Spain...
Cherrs,
JM