At least on my 91 300SL, the screw needs to be pressed down to engage the actual adjuster. Before you go too far, press on the screw while running to lean the mixture then turn slightly to engage the adjuster and pull up slightly to richen. This will give you a idea how far you are off. Past that I have not done much with this system.

Also, on this car it had been sitting for 3 + years with old fuel. The fuel distributor plunger was sticking causing all sorts of running issues.