if you have the idle screws all the way in that thing should be screamin... changing the clip position on the needle will only effect how rich the high speed is ( 3/4 throttle and up)
If you were turning the idle screws in, you were richening up the idle circuit, which could in effect cause the idle speed to slow down because you were giving the engine more gas than it really needs to idle properly.
And just to clarify, the idle screws most of the time have ridges or bumps and are totally exposed so you can turn them with your fingers, idle mixture screws can be slightly recessed into the carb body, and must be turned with a small flat blade screwdriver.