Thanks for your responses, Steve and Vaughn. I was reading somewhere that for moving the fuel misture screw, I should press down with the wrench - is that true?
One more issue. How harmful is it for the car if its running rich (fuel consumption up by 10-15%) - in terms of carbon build up in the engine, and clogging up of the cat. converter. My mechanic said - "Oh its fine, it won't hurt your car". But I'm not so sure. Any insights/experiences would be greatly appreciated.