The picture that you have posted doesn't correspond to the carburetor of your engine.
The one in the picture has a little hole at front for air intake thru the low end bolt.

If your carburetor is this one:

http://www3.towerhobbies.com/cgi-bin...&I=LXEGK8&P=RF

You have two needles that control the flow of fuel.

Study this information:

http://www.blacksheepclub.org/tuning.htm

Copied from that link at Tower Hobbies:

"Adjustable control on a carburetor used to set proper fuel/air mixture. Some carburetors have separate needle adjustments for low and high throttle. Typically, turning the needle clockwise (screwing in) leans the mixture (less fuel), and vice versa. However, there are a few exceptions - refer to the engine instructions."