Wzak,

My suggestion would be to find someone that is experienced to help you on your first try in tuning your engine.

The screw with the lock nut is used to adjust the travel of the carb barrel and in most cases also serves as its retainer.

The blue ring with the pin is a stop limiter for the low speed adjustment this is often a problem in getting the engine adjusted if the factory setting is not correctly set within the limited movement offered by the pin stops. It often has to be removed and repositioned in order to properly set the low speed needle.

The screw inside the blue ring is the low speed adjustment needle which needs to be adjusted to where the engine transitions from low speed idle to full power smoothly without bogging or quitting. If it bogs before coming smoothly up to power its too rich. This is most often accompanied with a great deal of engine exhaust. If the engine is too lean it will quit when the throttle is opened quickly for full power.

An easy test called the "pinch test" used while the engine is running after the high speed needle adjusted with the speed at idle pinch the fuel line to the carb closed. If the engine speeds up the mixture is too rich. If the engine quits its too lean. Make small adjustments about an eighth of a turn at a time. It may require removing the blue ring with the pin in order to make the proper adjustments.

Hope that helps.