The Stihl weed eater is built using a two-cycle engine. The carburettor of the engine provides air to the incoming gasoline to create the combustion necessary for mechanical movement. The carburettor needs adjusting if the air and fuel mixture is uneven. If either the fuel, or the air supply is too high, the engine will cut out or sputter, using fuel and oil inefficiently. Stihl carburettors have adjustment screws that let you change the air and fuel mixture in the engine.
Turn the high-speed screw, marked 'H' counterclockwise until it stops.
Tighten the 'L' screw all the way, then turn it one turn counterclockwise to open it.
Start up the engine and allow it to warm up. The cutting tool will rotate. Adjust the 'L' screw clockwise until the cutting tool stops moving.
Press the trigger of the machine to rev the engine. Adjust the 'H' screw until the engine does not cut out or sputter.
Turn the 'H' screw 1/4 turn for every 3,300 feet above sea level you are operating the unit.