My theory is, when the carb is brand new, the pilot system works great and the bike is easy to tune to get a nice tickover. As the slide wears excess air gets in buggers up the tick over resulting in a likely rich setting to compensate.
If the slide is flapping about then try a new one. You will need to hone out the slide bore as well before it will fit. New jets and needle and a good swill out and it should make it better.