Motorcycle Questions? Ask a Mechanic.
As long as you are sure there are no leaks of air coming in from the intake area, and the airbox and air filter are all in stock configuration. And as long as the exhaust is stock, then it would be safe to assume that the pilot jet in the carb is plugged or has some buildup in it. The problem going away with the choke being pulled out is the biggest clue here. That pilot screw adjustment that your trying should be enough so at this point it would be lacking the fuel from the jet in the carb. its the smallest jet in the carb, you get to it by taking the bottom float bowl off and taking it out with a small screwdriver. run a very fine wire through it to break out any buildup, that with some aresol cleaner will help clean it out well and likely take care of this issue.
it seems there still may be a lean spot. when did this atv start acting up? at random while still using it daily? or after it has sat unused for a while?