One good idle mixture adjustment method is to use a vacuum gauge, attached to a source of full manifold vacuum like the windshield wiper connection. With the idle speed set close to correct, richen the mixture screw (counterclockwise), until the best vacuum reading is achieved. If necessary, slow the idle down, and recheck the vacuum. Once it's max, richen the mixture screw about 1/8 turn, to give a good transition from idle to midrange speed. This method works well on early engines, before emission controls were used. Try it on a late-70's or newer engine, and you'll be WAY over-rich!
Jerry
