Welcome to the site !!
If you are positive the valve lash is correct , then you need to look into the carb more ..... did the bike sit for longer than 2 or 3 months with gas in it ??? , does the bike pop or backfire on deceleration (when riding and you let off the gas does it pop thru the muffler ?) , have you checked and or adjusted the fuel screw to see if it makes it worse or better ?? , (fuel screw is located at the bottom of the float bowl at the front of the carb *intake side* ) , The valves would be the most likely suspect , as that is where the symptoms start , is harder to start then progresses to running bad or stalling frequently , then not running at all when they finally close up , though it could also be a CDI or Stator issue , so you need to rule those out as well .......... When you checked the valves what were the readings ???
Also , Do you have a Owners or Service Manual ??? , this will help you perform the needed tests to rule out each item
My first guess would be valves , followed by carb ....... more detail in the symptoms and when/how they started would help as well , since there are many variables here that you have not explained ..........
Here is what you need to verify.....
The valve lash (what were the readings ??)
When the carb was cleaned , How was it cleaned ?? , and when you took off the bowl was there any green film inside the bowl bottom or anywhere inside the bowl or jet area ?? , were jets replaced or just cleaned and if so how were they cleaned ?? .... did you use carb cleaner spray without disassembling the carb ??
Did the bike sit as mentioned for more than 2 months with gas in the tank and more importantly in the carb ??
What did the plug look like when you pulled it ?? (white , gray , dark sooty ,tan)
Have you checked the spark ?? , if so was it bright blue or yellow/orange ?? , and was it consistent , or a intermittent spark ??
What is your starting procedure ?? , and was/is it the same before this issue and how did it start then ??