The Stihl gas trimmer uses a filter to removes contaminants from the fuel before it enters the carburetor. The gas filter is inside the fuel tank on the end of the incoming fuel line. When your Stihl becomes difficult to start or often stalls even with a full tank of fuel, chances are the fuel filter is dirty. Changing the gas filter on a Stihl trimmer is similar to any other brand. Stihl filters are available through Stihl authorized dealers and home improvement centers.
Search for the sparkplug and plug wire on your Stihl gas trimmer. The sparkplug is near the top rear of the trimmer engine housing. The sparkplug wire boot is the portion of the wire that connects on the top of the plug. Grasp the sparkplug wire boot with your fingers and pull it off the sparkplug. Bend the wire to the side so that the boot does not accidentally touch the sparkplug.
Twist the fuel cap counterclockwise and remove it from the fuel tank. Siphon fuel from the fuel tank into a container with a hand siphon. Dispose of the fuel properly.
Look inside the fuel tank for the fuel line laying in the bottom of the tank. The gas filter, or pick-up, is on the end of the fuel line. Pull the end of the fuel line and the gas filter out of the fuel tank with needle-nose pliers. If necessary, tilt the trimmer to move the fuel line closer to the tank opening to better grab the line with the pliers.
Grasp the end of the fuel line with your fingers and pull the gas filter off the end of the line with your free hand.
Hold the fuel line in one hand and push the stem of the replacement filter into the end of the line with your other hand. Push the filter until the end of the fuel line is flush to the top of the gas filter.
Push the gas filter into the fuel tank and shake the trimmer back and forth until the fuel line and gas filter are resting in the bottom of the tank. Fill the tank with your fuel/oil mixture and push the sparkplug wire boot over the top of the plug until it locks.