The enrichment circuit is for decel poping but does it by adding fuel , never thought of it as a source for richening the mixture at a steady throttle , but maybe it can. The plunger behind it is free and the spring good ? What about the idle mixture screw ? it does add some fuel beyond idle. Have you tried to see the difference between say 2500rpm ,3500, 4500 rpms to see if it gets worse or better ? I have one set of carbs for my XT's that I have the smallest pilot jet (42?) I can get plus the mixture screw is only out 1/2turn just to get it lean enough at low rpms ,the primary needle is shimmed down as much as it can in that setup ,plus the mains are on the small side as well but closer to normal. I have swapped sets around on several of my XT's and that set always runs extremely rich ,have never seen a reason why. Changed every part around as well , no clue, but it starts and runs the bike it's on right now very reliable, even in the cold, so I don't care to mess with it right now. .