The gasoline powered Stihl weed eater usually starts at the first pull or two of the recoil starter cord. Once started, this machine runs smoothly throughout its power range. Because these weed eaters are adjusted for efficient running at sea level, you will have to lean down the fuel air mixture to compensate for lower barometric pressure and reduced oxygen content at an elevated terrain. Once the machine is running and idling correctly, no further adjustment is necessary.
Remove the central screw in the round carburetor cover on top of the unit. Pull the cover off without turning it. Remove the foam air filter element from the housing. Wash the element in warm soapy water. Dry off and replace. Turn the filter cover to "Run." Start the weed eater and check that it runs and idles smoothly. If not, go to Step 2.
Remove the rubber spark plug cover. Wipe the plug, rubber cover and plug lead clean of any oil or moisture. Replace the rubber cover.
Examine the cutting head to ensure that it's mounted correctly. Pull the trim lines out and cut to the correct length. The end of the lines must be level with the limiting blade on the deflector.
Start the engine. Insert a flat screwdriver into the hole marked "LA" on the carburetor cover. Turn the screw either way to adjust the idling speed until the cutting tool stops rotating. Then turn the screw back a half a turn from that position.
Warm up the engine. At high altitude, turn the high speed adjusting screw marked "H" and the low speed adjusting screw marked "L" clockwise in small increments until the engine is running smoothly at full throttle and at lower speeds. This sometimes necessitates turning the screws as far as they will go. Repeat this procedure if you live at or near sea level, but turn both screws counterclockwise, or as far as they will go.
Re-adjust the idling speed after setting the correct fuel/air mixture by repeating the actions outlined in Step 4. If the machine idles erratically and has poor acceleration, turn the low speed adjusting screw marked "L" counterclockwise until the machine accelerates smoothly to maximum revolutions.