QianJiang 150-19A

[Zorge]

Post a picture of the carb and I'm sure someone can point you in the right direction.

Or directly to advise a man to look for brass screw with spring at the body of the carburettor.

[zhu]

odd that it has no idle adjustment
you can always adjust it at the cable ...
just alter the cable length while the bike is running
when it idles without holding the throttle
job done