Calling The Carb Experts

My buddy that i hunt with picked up a 05 Rubicon 500 TRX500FA around the same time i got my Rancher. The bike runs great and everything works. The only issue is a random idle issue, im sure cleaning the tank, shutoff valve and carb would fit the issue but would like to get your guys thoughts. The issue is the bike with crank up and idle fine and then after it warms up it doesnt want to idle, it will crank right up with applying a little throttle. He turns the little black adjustment knob on carb and gets it to idle again, he will go ride it and then it starts to idle high, adjust the knob again and lowers the rpms, after riding it again it doesnt want to idle. So basically he is fighting no idle/high idle. Its clearly a fueling issue and a simple cleaning would fit it im sure.

This is a generic carb pics off the interweb, not sure if this is the exact carb thats on his bike but it does have the 2 features that id like to get more info about.



What is that black knob adjustment for? Idle only?

Also see the other black handle just below the knob? When you pull that out with the bike running it kills. What is that?

Once hunting season is over im going to dive into it. Chances are hes going to want to just put a new carb on it($200) vs the down time of me rebuilding it. Regardless im going to rebuild it any tips?

Wayne