As Minn said, the small screw with the arrow pointing to it is the idle mixure screw, not idle speed screw.

If the engine idles reliabliy and transitions well, then it's fine, don't mess with it. From your question, I'd say leave this one (and the limiter device) alone, it's not your "problem" at all.

However, if you can't get the idle speed down slow enough, the black unlabaled screw in the picture will often stop the barrel from closing all the way.

Here's how to check. Disconnect the throttle linkage from the carb. Now, try to close the throttle with your fingers (engine NOT running here, btw). Look down the carb throad. Is the barrel fully closed? Or did the throttle arm hit against something that prevents the barrel from closing all the way?

If the barrel can not close all the way, back out the black unlabeled screw just a little bit. Now try to close the barrel again. If the throttle arm moves freely, and the barrel can be fully closed, you've got it right.

Note: some carbs have two screws on top, like in the picture I'm attaching. I don't think the Evo carb is like this. But if you do have a second screw up top that isn't visible in your picture, the screw you can't see is the one you want, and the black one in the picture just holds the barel in the carb. If you only have 1 screw up top, then it's a combination screw that both limits the carb travel on the low end, and prevents the barrel from falling out. OS carbs (at least the old ones) use a combination screw like this. I think the Evo is like this too.

Ok, so if you can close the barrel all the way with out the throttle hooked up, now hook up your throttle servo and check the movement the servo gives it. When the throttle trim in the full down position, and the stick full down, the barrel should be totally closed. If it's not, adjust the linkage (or ATV/End points/servo travel on the TX if you have it) until the throttle does close. Now move the trim to the full up position, with the stick still full down. The barrel should open enough for a solid idle that will be good for acrobatics and such. Somewhere in between will usually be your lowest idle that the engine will run at.

Also, keep in mind that new engines don't idle as well as ones that are well broken in. And smaller engines don't usually idle as well as larger ones. So you shouldn't expect a new .46-.61 to idle much below 2krpm out of the box.