I've recently acquired a Mk4 Escort fitted with one of these carbs and thought I'd better check everything's setup correctly so earlier I had a go at adjusting the idle mixture with a colortune. The screw I used is the one shown in this diagram, correct?
http://www.gowerlee.dircon.co.uk/TLDMtype.html (6)
The screw will only adjust roughly 2 turns in and out before going stiff and it seems to make absolutely no difference, am I doing something wrong?!

Thanks.