To set idle mixture screws: 1.Get the engine up to temp 2.Shut the engine off 3.Install a vacuum gauge to a full manifold vacuum port 4.Turn the screws all the way in until lightly seated 5.Back them out 1 full turn and restart the engine making sure the choke is completely off 6.While at idle, back them out 1/8 turn at a time, alternating between the 2 or 4, until highest vacuum is achieved. Be sure you keep all 2 or 4 screws even. You can also do this adjustment without a vacuum gauge, the adjustment are the same except you will adjust to highest engine RPM at idle.