Hi Grum,
testing the starter relais resulted in confusion - maybe some kind of a loose connection? The next day I found out, the cable just behind the connector has a kind of cable break.
Second problem was a dirty fuel filter. Only with a full tank threre was enough presssure in the fuel line to spend enough fuel for the carbs. Below 40% of tank volume I had
the issues with unclean motor operation...
So right now with new spark plugs, a new fuel filter and some typing on the connector cable at the starter relais, my bike runs pretty fine 😉
I am happy again! (and learned a lot)
Thanks for helping!
Joe