Heres a link to a picture of the carb transfer slot. Pull your carb and turn it upside down, now turn down the idle screw for the front butterfly to a point where the transfer slot looks like a square. Thats where you will leave it. do not close it all the way. Put it back on the car and try to establish a baseline idle off the rear butterfly adjusting screw only. If you can do that with minimal adjusting with the port plugged off, then you can readjust your idle air/fuel screws. Hope that helps you out. Skip
http://www.mustangandfords.com/techa.../photo_19.html