Hmm, I do know the slack you mean, I remember seeing it - the linkage has movement which doesn't adjust the throttle butterfly. I have still adjusted mine so that this is completely removed, however, using the thumbscrew - just let it tighten until the revs rised on the idleing engine, then turned it back a little. My 190 is injection (it's a 190*E* - Einspritzer = injection), but i've never looked at a carb one.
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black