GPZ 400 rotational speeds fluctuate at idle

Moin moin the following problem: recently got me a Kawasaki GPZ 400 of 86 with 33,000 km. Carburettor still needs to be synchronised and possibly cleaned. If I drive now and chop out the speeds are normal.In standing, however, I drive then 2-3 minutes and then stand again at the ampel my revolutions at about 4000. Choke pull and stand gas screw are also quite loose, means the Choke will probably adjust itself during the ride, however, will not My question is now after your experience, whether it can only be due to the stand gas screw and the choke, or also to something else? Greetings Mirko Edit: during the ride everything is normal, every now and then she tries if I don’t give any gas however not to drive with 1200 revolutions but with 3 in the 2nd gear for example