Remove the carburetor's limiter caps if equipped. Be aware that this may void your warranty, so remove them only if you are certain that your carburetor requires adjustment beyond the limiter's setting.
Start the saw and let the engine warm up completely. Never adjust the carburetor on a cold engine.
While idling, turn the "L" screw clockwise all the way in until the engine makes a higher-pitched whine. Back the screw out one-quarter turn and note its position. Then turn it back counterclockwise until the engine starts running rough or dies. Turn the screw back one-quarter turn and note its position. Set the screw halfway between the two positions you noted. Listen to the engine and test throttle response. The rpms shouldn't be too high or too low, and it should accelerate properly.
Holding the throttle in the full throttle position, turn the "H" clockwise until the engine starts making a very high-pitched whine. Back the throttle off, and back the screw off one-quarter turn immediately, since overspeeding can quickly ruin the engine. Hit the throttle again and turn the "H" screw counterclockwise until the top speed starts noticeably falling off. Turn the screw clockwise one-quarter turn. Adjust the "H" screw in between these two noted positions. These positions are the lean and rich drop-offs, respectively. Listen very carefully to the engine for the best reponse to the throttle, indicating the mixture is neither too rich nor too lean.
Finally, you adjust the idle speed to just slower than when the clutch engages.
Hope this helps!