How to Test a Coil on a Weed Eater

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The ignition coil on a weed eater is the strong electrical current that fires the spark plug. This in turn ignites the fuel in the cylinder. If your ignition coil stops working, the weed eater will either slow down or stop running altogether. However, it can sometimes be difficult to determine if the coil is what's causing the problems with your garden tool. Testing the ignition coil with an ignition system tester will reveal if that part of the weed eater is causing the problem.

How to Test a Coil on a Weed Eater
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How the Ignition Works

Three major parts comprise the ignition system: a magnet, which is located on the flywheel, a spark plug and the weed eater ignition coil. When it's time to start cutting weeds, you pull the cord and the flywheel rotates. A current is induced once the flywheel spins past the ignition coil, and this current moves through the wire to the spark plug. The traveling of this current to the spark plug creates a spark that ignites the fuel-air mixture in the chamber. This process is what makes the weed eater start.

Ignition coils tend to burn out over time or develop increased electrical resistance. This can lead to misfires or a weakened, less-efficient spark. If the spark starts having problems, your weed eater will too.

Testing the Weed Eater Ignition Coil

The easiest way to test your weed eater ignition coil is to use an ignition system tester. These testers are fairly inexpensive, simple to use and can be bought online or at your local hardware store. To test your weed eater's ignition coil, connect the tester between the spark plug boot and the engine.

Then, when you pull the starter cord, watch for a spark in the tester window. This type of tester can be used on any tool with a small engine, including a weed eater, a chainsaw or a snow blower.

Weak Spark vs. Strong Spark

When testing your weed eater with the system tester, you are watching for a spark in the test window. If a weak spark appears in the window, this means you will need to replace the ignition coil. If you see a strong spark but the weed eater still fails to start, you can try cleaning, regapping or replacing the spark plug, and then try the test again to see if the spark is stronger.

Always Practice Safety

The ignition systems in this type of weed eater can carry a lethal charge. This means you must take the necessary safety precautions when working on them. Make sure to set the trimmer on the ground. Wear work gloves made of leather. Be sure that you disconnect the HT lead wire from the tip of the spark plug when troubleshooting.


Heather Skyler is a journalist and novelist who has written for wide variety of publications, including, The New York Times and SKY magazine.

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