The Moto-Guzzi Nuovo Falcone VOC

Could be any number of things.
The only adjustment is the pilot jet which has little influence above tickover.
When my plug has fouled with soot, it's usually been caused by failure of the coil (twice) and condenser (once).
If you're sure it's carburettor, the first thing to check is the enrichener plunger. There's a rubber seal at the bottom which is supposed to stop fuel passing except when the enrichener is open. The rubber hardens and perishes, and can then allow fuel to pass even when the enrichener (choke) is closed.
Obviously, make sure the cable for the enrichener is seated and adjusted correctly, so the plunger is fully down.
That's the most likely cause.