Honestly, carburettor is the LAST thing you adjust. Because you can do so much with it a lot of the time people inadvertantly tune the carb so that other issues go away, and if those issues are for instance with the ignition system then you're on a one way street to **** City. You'll never get it all sorted.
SO- order of service for me goes-
1. adjust valves while engine is cold. Leave the car overnight if you want to do them properly.
2. Ensure dwell angle is correct on your points (Ideally with a dwell meter, they're about £20 and they're much more accurate than a feeler gauge)
2.5. Check spark plug gap and have a look at the colour. Clean or replace spark plugs as necessary (they last longer than you'd think though)
3. Adjust timing using a strobe light and a static light (indicator bulb etc). I use my static light to get the distributor set in the right place (nice and quiet without the engine running) and then check it with the strobe to make sure the advance is working OK and it settles in roughly the right place.
3.5. If you're going to do it, change the air filter or air filter oil. Don't do this after adjusting the carb, same with meddling with the exhaust- it alters the flow through the carb so you have to re-set the carb.
4. let the engine run, make sure there are no leaks in the inlet manifold (evidenced by RPM swings ("hunting") or whistling noises. Adjust carburettor as per the VW-resource manual here:-
http://www.vw-resource.com/34pict3.html" onclick="window.open(this.href);return false;
make sure that you're 100% clear- regarding the mixture, out is rich, in is lean. That webpage had it backwards for a while. I use a Gunson CO meter which takes all of the skill out of it, you just adjust a screw until you get a number.
In regards to your original question- that screw is JUST for the choke. Don't use it to adjust the idle speed. It should never rest on the lowest step, there should be a tiny (sheet of paper thickness tiny) gap between screw and cam when hot.
5. Let the engine warm up then change the oil and clean the strainer.