Hello gasgasman,
as I wrote, I do not set the mixture screw (Klicker) to adjust idle speed, but to adjust immediate return to idle after open throttle.
Of course I first tried to adjust the SC exactly as described in the manual. That left me with a stalling engine - always.
For the fuel I expect some influence, but no unadjustable problems, when using standard pump fuel that works with other Carb on same Bike and all my other bikes.
I will follow siaknijustin advice and see KTM-Talk too.

Thank both of you for your answers!:)

Best regards, Erhard

Adjusting
 

As I have some issues with my keihin 38 (leaking and too little power from low) I started to look for alternatives. Yes,I have been working at jetting and float height ;-)
After reading your struggles to adjust the smartcarb I think, I'll try to get along with my stock carb...
Or is the sc (or the lectron) with all its issues still better and easier to get along with than stock keihin?
As I live in Austria, the overallcosts are to high to make some unnecessary experiments

Look into upgrading your carb with the STIC product. It replaces the jet block. 275 USD.

How about some more info on this STIC product socalscott?

I'm guessing this is the product:
http://www.sticsupertorque.com/index.html

Not much for details on the webpage, and the videos just show a running CR125. I would like to know more info as well, but the page just asks for money on trust, which isn't confidence inspiring to me.

Edit: There is an installation video on the video page (who knew? :)). It looks like it uses the same needle and main jet, but the block holding the jets (metering block) is replaced. There is another video on youtube with a few more installation details:
https://www.youtube.com/watch?v=FCyW6Ads2kA

It looks like the STIC makes the Keihin similar to a Mikuni with an exchangeable emulsion tube.