Most two-stroke Weed Eaters operate with a capacitor discharge ignition system. These ignition systems produce a high voltage charge, which travels from the ignition module to the tip of the spark plug. When the Weed Eater doesn't produce a spark, you must test the entire ignition system to locate the source of the problem.
Replace Spark Plug
The ignition systems in the two-stroke Weed Eaters carry a lethal charge, so always take the necessary safety precautions when working on them. Wear leather work gloves, put the trimmer on the ground and always disconnect the HT lead wire from the tip of the spark plug when troubleshooting. Unscrew the spark plug from the cylinder and replace it with a new one if the tip looks black, bent or broken in any manner. Set the new plug aside while further testing the ignition system.
Use Test Plug
A test plug allows the operator to test if the spark is traveling from the ignition module to the spark plug. Hook the test plug onto the HT lead wire's boot and clip the test plug to the cylinder, which keeps the circuit properly grounded. Pull firmly on the starter rope and check for a blue spark. If a spark occurs, the problem was with the spark plug. If no spark occurs, the problem lies further into the ignition system.
Inspect the boot on the end of the HT lead wire, making sure no debris clogs up the connection point between the plug and the wire. Also make sure the metal tip inside the boot isn't bent or damaged and the boot is securely fastened to the HT lead wire. Check the entire length of the HT lead wire for damage, corrosion and loose connections. Inspect the short-circuit and lead wire, as it runs from the module to the ignition switch. Replace any damaged or frayed wires and repeat the spark test.
Ignition Module Replacement
The ignition module houses an electrical coil. This coil produces and fires off the high voltage charge. If all the wiring and spark plug check out through testing, replace the entire ignition module. Never try to separate or open up the ignition module to take out the coil, as it can still carry a charge long after it's disconnected. Also, inspect the condition of the flywheel magnets and replace the flywheel if the magnets show a dark blue or black discoloration.