On the right side of the carburator there is a screw with a spring, it is the fuel air mixture needle.
Start the engine and let it idle until it warms up, make the adjustments at idle. Turn the mixture needle in slowly until the engine starts to idle rough and make a mental note where it's at.
Turn the mixture needle out slowly until the engine smooths out, keep turning until the engine idles rough again, then turn the mixture needle to the middle of the two positions and check acceleration by giving it full throttle. If it revs smoothly and runs smoothly your done, congratulations you adjusted your carburater.
Is the throttle lever located on the engine or the handle bar?