Does the air butterfly snap to when the throttle is closed?
If not, the throttle linkage may be boogered; I'd check the spring and the two throttle cables (i.e., the OPEN and the CLOSE cable) for free travel of the air butterfly.
Air butterfly snaps to, but the problem persists? Then, I'd check the slide for free up-and-down movement; slide could be sticking in its grooves, or slide spring compromised.
If the final idle speed is within specs, doesn't sound like idle adjustment screw is out of whack, or serious jetting problems exist.
Assume the "choke" (starting enricher) plunger seats fully in the carb when the choke lever is in the OFF position.
When the throttle is closed, so should the air butterfly close, immediately. With the intake airflow cut down, the slide should drop from the force of the slide spring very soon
thereafter, since airflow vacuum alone raises the slide, uncovering needle and main jets providing fuel to the engine.
Here's how your carb works: http://www.gadgetjq.com/keihin_carb.htm
I consider adjusting the fuel screw fundamental (although it dominates only the idle air/fuel mixture); I'd recommend 1.75 turns out as a starting point for a stock bike.
Valve clearance should be of no consequence to your open-throttle-to-idle transition problem, seems to me.
The unknown magnitude and conditions associated with running "hot" make prospective diagnosis difficult, for me.