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How to Troubleshoot a Weed Trimmer

Though some string trimmers run on battery power or corded electric motors, two-cycle gasoline engines power most versions. Owner's manuals provide step-by-step procedures for isolating and correcting minor issues. Following recommended maintenance steps prevents most common problems. Serious trouble could be covered by warranty services.

Troubleshooting Line Trimmers

Check the power cord first if an inoperative electric line trimmer plugs into an outlet during use. Cords could be damaged by mowers. Plug prongs may not be connected at the wall outlet or the cord could be poorly connected to the trimmer. Re-seating the plug could restore power. Replacement cords solve most intermittent power faults in this type of trimmer.

Check the battery if a rechargeable trimmer spins slowly or runs for only a short time. Plug the trimmer into its cradle and charge the battery properly before use. Batteries more than two years old could fail to hold a charge. Replacements are often available from the manufacturer.

Review the starting procedure if a gas-powered trimmer won't start. If the trimmer was stored over the winter with fuel mix in the tank and will not start in the spring, empty the tank and add new mix. Use fresh gasoline. Add oil to the gas in the recommended ratio, which varies from model to model.

Check the air filter if the trimmer starts but runs poorly. Trimmers need a warm-up period at half choke before opening the choke fully. If the trimmer won't run at the correct speed and exhausts thick blue smoke, turn the machine off and remove the filter cover. Dirty filters may be rinsed in clean gasoline and thoroughly dried, or replaced with new filters. Don't clean filters in a gas/oil mix.

Clean the spark suppressor if the trimmer runs well for a moment and then gradually dies. A clogged screen at the outlet of the exhaust will suffocate the motor. Use a screwdriver to remove the screen and clear the mesh with a small wire brush. Replace the screen before use—it prevents burning carbon from starting grass fires.

Examine the cutter head if the trimmer runs but the cutter doesn't spin. Grass or weeds wrapped around the shaft could be jamming the bearing. Pull or cut them loose until the head turns freely. If the head turns easily in the hand but seems to have no real connection to the motor, the shaft or gearbox could be broken. Warranties may cover the repair.

Check the line if the cutter head spins but the trimmer cuts poorly. Line often jams in automatic feed spools. Remove the spool and look for over wraps. Pull enough line free to remove the tangle and rewind the line correctly. Replace the spool in the head. While running the trimmer at working speed, bump the head on a solid surface to release more line.


Always turn off the trimmer and disconnect the spark plug wire before working on the machine. While many owners immediately suspect a bad spark plug, plugs seldom fail. Use a plug wrench to remove the spark plug and inspect it for unusual wear. Replace if needed. Dirty plugs indicate combustion problems.


Leave carburetor settings alone. Most are preset and capped at the factory to prevent owner adjustment. Other factors cause most trimmer problems.

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