fuel metering head CO mixture screw

Hi chaps and chapesses, a friend and I were tinkering with the fueling and mixture on my 83 gti and hve mucked it up ; if I was to tighten the screw on the meeting head right up,at what degree should I unwind it to set it to what It would originally be?? I keep tinkering to try fix it but am having noooo joy!!!  ANY help would be muchly appreciated!! Cheers

a photo of what your looking at might help.
If its the idle air screw in the back of the throttle body, make sure the O ring on it isn't flattened out.
Otherwise you can suck in too much air and not set the RPM correctly.

Thank you for your reply,It's the 3mm hexi screw on the meetering head that I need to change back to stock.thanks

A ha thought it was the idle screw.
But that's worth looking at also.
These often shrink or get a flat spot so send the car running funny.

You really need to get it hooked up to a Exhaust gas analyser to read the CO, a garage which does MOT will have the equipment to check it.
Before setting the Mixture you need to make sure the car is fully serviced with a clean air filter and timing spot on then get the mixture adjusted as that's the last thing to mess with.
1.5 to 2 % is what you are looking for.

Thanks for all responses guys,really appreciate it