A four-cycle Troy-Bilt weed eater operates with an internal combustion engine using two cylinders in a four-stroke movement. This engine uses the same, unmixed, regular unleaded gasoline, as in lawn mowers, unlike the oil-gas mix found in most trimmers. Fuel will cause a wide array of problems that can shut down the fuel, spark and air systems. Troubleshoot the spark, air and fuel systems to locate the source of the problem and make further repairs as necessary.
Wiggle up the rubber boot on the end of the HT lead, lifting the cap off the end of the spark plug. Unscrew the spark plug from the cylinder. Fit the test spark plug into the boot at the end of the HT wire.
Place the trimmer on the ground. Connect the test plug to a ground metal point on the engine block. Hold the trimmer steady and crank on the starter rope. Look at the test plug for a blue spark to jump across the point.
Take the test plug out of the boot, if the spark is yellow or absent. Check the metal prong inside the boot and the area around it for dust or debris. Make sure the boot is tight against the wire. Inspect the length of the HT wire back to the ignition system.
Follow the wiring from the ignition switch back to the ignition module. Look for pinched, frayed or damaged wiring, grounding the circuit prematurely. Replace any wires as necessary. Repeat the spark test; if the plug still doesn't arc blue, leave further ignition testing to a mechanic.
Unhook the test plug again. Screw the compression gauge tight against the spark plug hole with your fingers. Hold the trimmer steady and crank on the starter rope again. Check the reading on the gauge to hold steady around 100 to 150 psi. If compression drops rapidly or never rises, allow professional to inspect the air systems.
Unscrew the air filter cover and lift the filter out of the box. Wash it in warm soapy water and rinse it out, letting it dry for four hours. Unscrew the filter box and lift it away. Unscrew the choke cover plate underneath the filter box.