Did you ever figure out what is going on? I found on my sons 4 wheeler, much like you would do the same thing, that when I took the carb off to clean it, that I left the throttle cable cap lose and it was actually getting to much air. I s that possible? Either way I tightened that down and away he went with no issues.

 

40 is just part of the throttle stop and your air screw should be 27/8 turns out according to my manual. And im suffering from the opposite problem i cant start mine unless i take the airfilter off and put my hand over it and keep it there until i get it to rev up but then its fine.