That's your idel air screw! Don't run without it and it CAN NOT be replaced with a average run of the mill screw it's more like a jet honestly. should be 1 and a half turns out when reinstalled pretty sure, someone will correct me If I'm wrong.
There other screw they are referring to in the tors "brick" is your idel adjustment to. Take your seat off ( it's just a latch at the rear of the quad) and look down under your tank, do you see a goofy looking brick down there on top of your carb. If so the screw facing you on the top of this "brick" is also for your idel adjustment.