Before you make any modifications to your carburetor you need to get everything else set properly first.
First you've got get your ignition situation straightened out. Timing issues will affect how the engine idles.
From there you'll need to go through and baseline your carburetor. Setting the amount of transfer slot that is exposed on the primary, and secondary side.
If you can screw the indle mixture screws all the way in, and the engine still runs the engine has to be getting fuel from some place else. The next logical spot would be that the primary butterflies are open too far, giving the engine fuel.
What kind of RPM are you looking at idling the engine at?