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String Trimmer Won't Start

The string trimmer small engine often has a separate model number. Use the small engine model number for a complete list of symptoms and parts. Watch our model # lookup video for help finding the model number.

The 13 most common part(s) or condition(s) which contribute to the symptom String trimmer won't start are listed below. Check or test each item and watch any available videos. If you are still unable to solve the problem you may need to do additional research and troubleshooting. Remember, with our 365 Days. Period.® return policy you can return any part for any reason. So, go ahead and buy it to try it. No other parts retailer offers this unconditional return policy.


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For the symptom you selected, these are the most common parts or causes, ordered by the likelihood of fixing the symptom.

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Spark Plug

If the string trimmer won't start the spark plug might be defective. All small engines have an ignition coil. The coil is the device that provides spark for the spark plug(s). If the coil is bad power won't get to the spark plug(s). The coil is essentially a small, induction generator. It is mounted next to the flywheel. The flywheel has one or more strong, embedded magnets. As the flywheel spins, the magnet(s) zip past the induction coil, this action of a magnet passing past a coil induces a voltage. Depending on the design of the coil and the strength of the magnets, a stronger or weaker spark can be created and delivered to the spark plug(s). Each time the flywheel spins around a spark is generated. The best way to test a spark plug is to use a spark plug tester. The spark plug should have a strong, visible spark between the electrodes when the engine is cranking. If it doesn't, replace it.

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Carburetor

If the string trimmer won't start, the carburetor might be clogged or have bad fuel in the float bowl. If old fuel was left in the string trimmer for a long time some of the volatile ingredients may have evaporated, leaving a thicker, stickier product that is more like varnish or shellac. This sticky fuel can clog up the small jets and ports in the carburetor and it can be difficult to burn making it hard to start the engine. The only solution is to drain the old fuel from the float bowl and thoroughly clean the carburetor with carburetor cleaner. If that isn't effective, replace the entire carburetor.

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Carburetor Kit

If the string trimmer won't start, the carburetor might be clogged or have bad fuel in the float bowl. If old fuel was left in the string trimmer for a long time some of the volatile ingredients may have evaporated, leaving a thicker, stickier product that is more like varnish or shellac. This sticky fuel can clog up the small jets and ports in the carburetor assembly and it can be difficult to burn making the string trimmer engine run roughly. The only solution is to drain the old fuel from the float bowl and thoroughly clean the carburetor assembly with carburetor assembly cleaner. If that isn't effective, rebuild the carburetor with this carburetor kit.

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Safety Switch

If the string trimmer won't start the safety switch might be activated or defective. Watch our video on switch testing to see if this switch is good.

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Rewind Spring

When the starter rope is pulled and let go the rewind spring is supposed to recoil the rope onto a pulley. If the rewind spring is broken the rope can't be recoiled onto the string trimmer pulley which will prevent it from turning over the engine, and then it is hard to start. Many rewind springs can be replaced but it's sometimes easier to replace the whole recoil starter assembly.

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Rewind Pulley and Spring

When the starter rope is pulled and let go the rewind pulley and spring is supposed to recoil the rope onto the pulley. If the recoil spring is broken the rope can't be recoiled onto the pulley which will prevent it from turning over the engine, and then the string trimmer does not start. Many recoil springs can be replaced but it's sometimes easier to replace the whole rewind pulley and spring assembly.

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Recoil Starter

If the string trimmer won't start the recoil starter assembly might not be engaging with the crankshaft and turning over the engine. Remove the starter assembly to see if it is functioning properly.

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Recoil Starter Pulley

When the starter rope is pulled and let go the recoil spring is supposed to recoil the rope onto the recoil starter pulley. If the recoil spring is broken the rope can't be recoiled onto the pulley which will prevent it from turning over the string trimmer engine, and then it does not start. Many recoil springs can be replaced but it's sometimes easier to replace the whole recoil starter assembly.

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Fuel Filter

If the string trimmer won't start the fuel filter might be clogged. The fuel filter is usually inline with the fuel line coming from the gas tank. Its purpose is to trap sediment and contaminants from the fuel. Over time it can become clogged and not let enough fuel through. It can't be cleaned but must be replaced if needed.

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Spark Arrester

Inside the muffler of string trimmer engine is a screen-like device called a spark arrestor. If the string trimmer runs poorly or won't start, the spark arrestor might be clogged. The spark arrestor prevents small embers from being emitted by the engine to prevent fires. Over time the spark arrestor will become clogged with soot. Remove the spark arrestor and clean with a wire brush or replace.

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On - Off Switch

If the string trimmer engine does not start the on - off switch might be turned off or defective. Test the switch with an Ohm meter or continuity checker.

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Air Filter

If the string trimmer won't start the air filter might be clogged. Remove the air filter and replace with the correct filter.

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Flywheel Key

If the string trimmer engine won't start the flywheel key might have sheared in half. The flywheel key is a small metal shim which fits into a slot in the crankshaft and engages with the flywheel. If the engine experiences a sudden stoppage it can cause the flywheel key to shear. The only way to know for sure if this is the problem is to remove the flywheel and inspect the flywheel key.

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