Stihl makes several types of equipment that withstand high usage for professionals or homeowners who require extra power, dependability and longevity of their power tools. Engines on Stihl trimmers, chainsaws, blowers, edgers and cultivators are two-cycle. A faulty ignition coil will disable any two-cycle engine from starting because it will not allow the sparkplug to operate. Small engines need spark, fuel and air to start and run, so testing is of the utmost importance.
Automotive Coil Tester Method
Place the Stihl tool on a sturdy work surface. Start the test with either a cool or a warm engine.
Attach an automotive coil tester by placing the end of the tool with grooves over the sparkplug wire. Do not disconnect the wire from the sparkplug. Crank the Stihl equipment.
Watch the coil tester when cranking the equipment. If a light flashes inside the tool, there is sufficient spark in the sparkplug, indicating that the ignition coil is working properly. If the light does not flash inside the tool, the ignition coil needs replacing.
Remove any guard pieces that cover the Stihl tool by turning the screws counterclockwise with a Phillips screwdriver. There are one to two plastic covers over the engine area, depending on the tool.
Remove the sparkplug from its wiring harness by pulling it straight out. Disable the kill switch on the tool by unplugging it from its wiring harness. If you are not sure where the kill switch is on your tool, refer to your owner's manual.
Open the top ground of a new sparkplug so that is has a large gap. Replace the starter guard pieces with screws so that nothing may enter the starter as it turns and you will not accidentally touch it. Pull the starting cord to start the Stihl engine.
Crank the engine and observe the end of the sparkplug. If you see a spark jumping the gap between the top of the sparkplug and the ground, there is sufficient spark. This result proves that the ignition coil is working.