Mitcheman, Welcome to the group.
Before you do anything else with the carbs,,,,
It sounds like you have a carb problem, but do the simple thing first.
check the spark plug caps and wires.
Have you talked to anyone in the GCE Club (in Europe)?
(GTR Club of Europe)
As you are in the Netherlands,,, I know that several members of GCE live in the Netherlands.
NOTE: The GCE Club is putting on a Rally in Breda Netherlands August 1 thru 5.
Contact them and try to be in Breda,,,, lots of info will be available...
(4 COGgers {including me and my wife)} plan to be there)
Ride safe, Ted