It would be unusual for the carbies to go out of sync so quickly considering that the service was done last week abd it was running ok. If the bike ran OK and then has lost performance it would most likely be another cause.
The little black knob your adjusting is the idle speed adjuster.
If it's not idling well and sems to lack performance then you can either of two problems...fuel or electrics....(unless there's no oil in it or soemthing stupid like that)
my guess is that it might be a bit of crude in the fuel filter or maybe bad fuel with water in it or a honda rider is jealous of the kawasaki performance and is sabotaging your ride. Anything is possible really .
If it's not a fuel problem then it could also be electrical. You can do some basic checks...make sure the leads are on properly.....wires correctly fitted etc etc....did they change the plugs?? You could check them if you know how!
Otherwise it might be a case that you've got use to the enormous power of the 250 kawasaki engine.
I live with fear everyday but on weekends she lets me ride.