Normally when you get no response to turning the screws that means you have the idle SPEED screw turned in far enough that you are exposing too much of the transfer slot in the base plate causing you to pull from the main circuit rather than the idle circuit. Slow the idle down if you can and adjust it and I bet you will see a difference. If it won't run with it backed that far down you may need to drill holes in the throttle blades or flip the carb over and open the secondary blades a small amount with the little screw on bottom