I'm not certain what it is, but I think it is a slosh tray to keep the jet wet during heavy motocross activity.This is originally a motocross carbureter design.
It says you answered me at 6:11PM? Where the hell is it 6:11PM? It's 3PM here. Anyway. I've spent over an hour trying to fit that #@#%#^^ing plastic wheel thing back on to where it will stay on. I think I'm going bloody shithouse mouse crazy. I know it was on there when I got the carb, but the only way I see that it can go will not allow the Main Jet to screw in. It's NUTS!! And this isn't my first rodeo. I've had it. I'm leaving the Effing thing off. BTW I'm going to try the 27.5 Pilot again. I thought a had a reliable starter with the #30 at 3 turns out. But Nuhoooo! I'm back to thinking again that the #30 is too rich & that 3 turns out is too far (which was my thinking before).
Regarding the borderline jetting, that might be an issue. In warmer summer months, it needs leaner, and in cooler months it needs richer. Generally the 30 works fine for most applications, but for you it might be right on the borderline. You have a very unique application with different porting and chamber configurations than anything else that we have done. Yours might like it a little bit leaner than our other engines.
The pilot actually affects the entire mixture range by a small amount.And it does affect the transition off of idle, into the small throttle opening range.So, there is more to the pilot jet than just starting and idling.It can affect aspects of running too.