I believe Mrmiji means the jet needle on the end of the throttle cable. It has four grooves at the top. One of the grooves will have a little clip in it. The clip is what sets its position. The amount of penetration of the needle valve into the carb changes the richness or leanness of the fuel mixture. The position of the needle valve is usually modified after inspecting the spark plug color. If it is too dark it means the fuel mixture is too rich. If it is white it means it is too lean. Ideally you are looking for a desert tan color on the top of the plug. Correct me if I have this backwards but I think lowering the needle (raising the clip a notch) leans out the mixture and raising the needle (lowering the clip a notch) richens it.

Doug - Olympia - Washington
 I don't know how many CTs I have.