Troubleshooting a String Trimmer that has Lost Power

A few simple maintenance practices can help restore the performance of a faulty string trimmer.

Troubleshooting a String Trimmer

Check the Age of the Fuel

Today’s ethanol-containing gasoline can break down in relatively short time periods. If your blended fuel supply is more than two or three weeks old, blend a new batch of fuel.

Check Air Filter Condition

A clogged air filter prevents the engine from receiving sufficient air to operate properly. Before removing the air filter, brush away loose debris from around the filter cover and filter element. Tap the filter on a tabletop or the palm of your hand to dislodge any dirt or debris. If you use compressed air, make sure you direct air through the filter from the inside to avoid lodging debris deeper in the filter. Avoid washing the filter as this can collapse its micro-fine structure. If cleaning doesn’t remove debris, replace the filter with the appropriate part recommended by the trimmer manufacturer.

Check the Spark Plug

Spark plug fouling occurs when oil, carbon or other foreign substances coat the tip of the plug and interfere with normal firing. Too much oil in the gasoline, inferior oil, a dirty air filter and/or continued operation at less than full throttle will eventually cause spark plug fouling. Replace the spark plug with a new one recommended by the trimmer manufacturer.

If a new plug is not immediately available, remove the plug and clean all carbon and oil deposits from the plug tip. Set the gap according to the manufacturer’s recommendations and reinstall the plug.

Clean the Exhaust Spark Arrestor Screen

On many trimmers, a small screen covers the exhaust outlet and prevents sparks from exiting the muffler and potentially starting a wildfire. For this reason, trimmers should not be operated if the screen is missing, punctured or disintegrating.

As with plug fouling, too much oil in the gasoline, inferior oil, a dirty air filter and/or continued operation at less than full throttle will plug the screen with carbon deposits. This prevents exhaust gas flow, which leads to power loss. To fix the problem, remove the spark arrestor screen and inspect it for plugging. If plugged, either replace it with the appropriate part recommended by the trimmer manufacturer or clean it.

To clean the spark arrestor screen, spray it with AMSOIL Power Foam® to soften the deposits before cleaning the screen with an abrasive pad. Reinstall the screen and test the trimmer. 

If these attempts to restore power fail, take the trimmer to your servicing dealer.

Use High-Quality Oil to Help Avoid Power Loss

Using a high-quality two-stroke oil with excellent detergency can help avoid many of the problems listed here. Two-stroke oils that burn cleanly help reduce plug fouling and spark arrestor screen deposits. AMSOIL SABER® Professional Synthetic 2-Stroke Oil withstands high heat and stress to protect handheld equipment engines against wear and harmful deposits. It can be mixed at conventional mix ratios (32:1, 40:1, 50:1) or the SABER Ratio (80:1, 100:1), offering the convenience of one mix ratio for all applications.

*All trademarked images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are AMSOIL-engineered for use in the applications shown.

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