On my Mikuni VM round slide, the slide is close to being fully closed, and is actually kept from being closed by the needle seat below it. In reading your post, you mention that you have the throttle adjustors all the way "out." I believe that the adjustors should be "in" if you are wanting to achieve slack, or freeplay at the throttle tube. On my setup, you actually have two adjustors, one on the cable itself, and another where it screws into the top of the carb.