Air,fuel mixture screw on top of cab cover

Today at 10:18:51 AM

Hi everyone,
I got a vw golf mk2 Driver 1990 1600cc cab.
First question, someone fiddeled with the cab air/fuel screw on top of the cab cover, now it seems to use to much petrol,...
How do you adjust it properly

I tried a few times when car is hot but i-m un-sure if i screw too much or too less lol.

Second question, for this car what should the idle RPM be ? I've seen some saying 800 to 850, others 900 to 950 ?
What's best ??

Thank you very much,

Regards,

Phil.