Start the engine and allow it to warm up for five minutes. While the engine is warming up, find the low speed and idle speed adjustment screws. The low speed screw has an "L" stamp, and the idle speed screw has an "LA" stamp next to it. The screws are near the choke lever.
Rotate the low speed screw clockwise with a flat screwdriver until it seats fully. Do not force it to turn once it stops. Turn the low speed screw one complete revolution counterclockwise.
Turn the idle speed screw clockwise until the cutting blades on the Stihl HS-80 begin to move if the engine stalls while idling. Once the blades start moving, turn the screw 1/2 turn counterclockwise.
Rotate the idle speed screw counterclockwise if the blades move while the engine is idling. Once the blades stop moving, turn the idle screw 1/2 turn clockwise.