TOPIC:

Just bought a 1978 KZ200 with 4000 original miles on it. I had to install new carb float and jetting is stock.
Set the float level by the tube method. Set timing with timing light and everything has been gone through, adjusted to stock factory specs. 

Bike starts right up and never needs choke to start. Idles fine but once the engine is fully warmed up and I come to a stop it stalls out and will not hold idle. I adjust the air screw out to about 2 1/2 turns ( stock is supposed to be 1 1/4 turns out)
and turn in the idle speed screw to try and keep idle but I keep fighting between the two adjustments in an effort to keep it from dying at idle but to no avail.
When I check the plug after running on idle circuit, it is black and sooty. However the bike runs just fine off idle to full throttle and the plug reads excellent in that range.
I tried lowering the needle by one position, and adding one step leaner idle jet and although it seems to run a little better it still ends up loading up at idle and stalling at stops from the rich condition at idle. Just can't seem to get the idle circuit leaned out enough it seems.
Would sure like some expert advice, I am a pretty competent mechanic but I am stumped. 
 Edit
 

Is your choke plate closing at idle?
 

Try closing the petcock to see if the float valve is leaking.  Hows the battery/charging system?

No, the choke plate is not closing at idle the car is in excellent shape bike is only 4000 miles on it in the carb has been completely gone through. Jet needle clip is on second slot from the top.

No, the float valve is not leaking thank you.