On Holleys, if you have loosened the throttle blades, then you need to turn the carb upside down, remove the linkage to the secondary arm(both vacuum diaphragm arm and secondary linkage),  back off the primary blades to fully close them, back off the secondary blades to fully close them, and then loosen all eight throttle screws slightly so that the butterflies will move to center themselves in the venturi with the shafts fully closed.  Now tighten gently the eight brass screws and open the butterflies by hand to see if they will open to a full 90* wide open throttle, and then close them again.  Do they fully close?  If so then tighten them as much as you can by hand, and check again for WOT, and if they open and close smoothly, you can start your adjustments.  With the vacuum linkage installed again, the secondary throttle blades should be open enough to see .020" of the idle transfer slot showing.  You can adjust this by bending the linkage arm, or a set screw if the baseplate has that option.  Next install the secondary linkage arm to the throttle arm and you will probably only open the primary just enough to keep the butterflies from sticking(a very tiny amount).  Adjust the idle quality screws, and set the idle speed now with the vacuum disconnected and plugged to the distributor.  IF the idle speed is too high, close the secondary plate a tiny bit(.018") slot showing, and try again.  Idle speed is/should be controlled by the secondary blade position, not the primary as is commonly thought.  Hopefully this will get you back to a good idle quality.  Joe-JDC

JDC

The adjustment is made using the Idle speed Screw on the side where the Throttle linkage hooks up. Turn the Carb over and slowly back off the Idle screw until the Transfer slot BELOW the Throttle Plate looks like a Square. You do need to be sure the Choke fast Idle screw is off and not holding the Throttle plate open.

  

In an effort to adjust the transfer slots on my holley  4581 4 barrel to make them square shaped , I think I have totally goofed everything up. On examination, the slots appeared to be elongated to about an eighth inch and the only way I could see to shorten the slots to a square was to wind out the fast idle cam screw (manual choke) which I did until the screw and spring backed out all the way and fell out on the floor. I still needed more adjustment so I picked a long flat screwdriver and loosened the brass screws on the round primary throttle plates and was surprised at how much the plates would slide out of adjustment with me not knowing how to readjust them properly I am hoping someone can refer me to a source that illustrates how to seat and adjust the throttle plates properly and also what setting the fast idle cam should be set to. And finally if I can get everything back to where it was, How DO you adjust the transfer slot?  Edelbrock is starting to sound pretty good. Funny with several well meaning people advising me  and having sorted through numerous holley videos on line , I could find nothing telling me how to adjust the slot, only that it needed to be square shaped.  Thanks    George