Sometimes you’ll find yourself getting worn out by repeatedly pulling and pulling your weed eater’s starter cord. A lot of the time, this is down to the fact that there is some kind of issue causing your weed eater to not get a spark. So, what parts of your weed eater are actually responsible for making the spark, and what could be at fault? Let’s take a look.
Why Doesn’t My Weed Eater Get a Spark? (The Short Answer)
Five main items work together to create the ignition spark needed to fire up your weed eater. These include the magnet on the flywheel, the coil, the coil cable and connector, the ON/OFF switch, and finally, the spark plug. If either one of these components fails, your weed eater will not make a spark.
6 Possible Reasons for a Trimmer with No Spark (6 Things to Check)
If your weed eater is not getting a spark, then you’ll need to take a closer look at the four components responsible for creating the ignition spark. Here are six things to check to diagnose the root of the problem.
- Bad Spark Plug
- Poor Connection Between the Spark Plug & Cable
- Incorrect Coil/Magnet Gap
- Corroded Coil & Magnet Contacts
- Faulty Coil
- On/Off Switch Connection
Bad Spark Plug
One of the first things to check if your weed eater is not getting a spark is the spark plug. A spark plug can fail to make a spark for a number of reasons. For example, the contacts at the end of the spark plug could be sooted up with carbon, the gap could be incorrectly set, or the spark plug could be burned out.
Now there are a bunch of tests you can do to test your spark plug, but the simplest and quickest is to try your weed eater with a new spark plug. If a new plug gives off a spark, then you’ll know the old spark plug is at fault. On the other hand, if the new spark plug also doesn’t make a spark, then you’ll have diagnosed that something else in the ignition system is at fault.
Poor Connection Between the Spark Plug & Cable
The next place to check is the connection between the spark plug and the spark plug cable. Sometimes this connection within the spark plug cable can either become damaged or dirty, resulting in a bad connection.
Usually, the connection between the cable from the coil to the end connector is sealed, so you can’t test just the cable by itself. If you test the cable through the coil, you could get a false reading because it could actually be a problem at the coil end and not the connector. So, all you can really do is take a look inside the connector and check for damage and dirt.
Incorrect Coil/Magnet Gap
For the coil to produce the required charge, there needs to be a specific gap between the coil and the magnet on the flywheel. If this gap is set incorrectly, then you won’t get the spark that you are expecting.
So, if you flip through your service manual, you’ll find the specific gap measurement for your particular weed eater. Once you know the measurement, you can check the gap using a feeler gauge and diagnose if this is the cause of your weed eater not getting a spark.
Corroded Coil & Magnet Contacts
Another pretty common issue with weed eaters is that the face of the magnet and/or the outer armature becomes corroded and reduces the coil’s ability to produce current. This has the same effect as having the coil incorrectly gapped from the flywheel magnet.
To check if these contacts are corroded, you will need to remove the coil from your weed eater and conduct a visual inspection. Usually, it’s pretty obvious if these contacts are corroded, as you’ll see some rust.
Faulty Coil
Next on the list of reasons your weed eater has no spark is the coil itself. Issues such as a bad spark plug or trying to start a weed eater without the coil grounded can cause irreparable damage to a coil. In addition, if you have ever pulled the start cord with the spark plug cable detached from the spark plug, you were actually burning out your coil. So, to check if your weed eater coil is burned out and needs replacing, you will need to test the coil using a multimeter.
The first test is to check the coil between the coil’s ground connection and the armature, and the second test is to test between the end of the spark plug cable and the armature. For both of these tests, you’ll need your multimeter set to resistance.
So, to understand what the two results mean, figure out your specific coil type and look up the manufacturer’s specifications for resistance. If your results are not the same or at least not very close to the original specifications, you’ll need to replace the coil.
On/Off Switch Connection
The last issue I come across that causes a weed eater not to spark is the connection of the on/off switch. What the on/off switch actually does is take the current away from the spark plug by grounding it to the metal frame of your weed eater. So, if there is a fault in the kill switch, your coil could potentially be permanently grounded, and your weed eater will never start.
To test the switch, you’ll need to set your multimeter to continuity and connect the two probes to either side of the switch. So, a good switch should have continuity when the switch is set to off/stop and no continuity when the switch is set to on/run. If you have continuity in both switch positions, then your switch is permanently grounding the coil. This means you’ll need to replace the switch.
How to Fix a Weed Eater That’s Not Getting a Spark (6 Ideas)
Now that you have been through the common causes for your weed eater not getting a spark, let’s take a look at the repairs. Here are my six step-by-step guides to getting your weed eater fired up and sparking like normal.
Weed Eater Spark Plug Replacement
One of the most important things about changing a spark plug on any engine is to make sure that you use the right spark plug. The easiest way to ensure you use the right replacement spark plug for your weed eater is to double-check in your owner’s manual.
So, once you have your replacement plug, remove the coil cable from the existing spark plug and tuck it to one side. Then, use a spark plug wrench to remove the old plug. Remember, lefty loosey, righty tighty. Next, place your new spark plug into the engine, and tighten it by hand until you can’t turn it any further. Finally, tighten the new plug with your spark plug wrench and reconnect the spark plug cable.
Tools & Parts to Replace a Weed Eater Spark Plug
- Spark Plug Wrench
- New Spark Plug Specific to Your Weed Eater
Repairing the Connection Between the Spark Plug & Cable
For this repair, you’ll aim to clean out the end of the spark plug cable to remove dirt and corrosion. Start by removing the cable from the spark plug, then twist it around so you can see into the connector. Then take either a small rolled-up piece of sandpaper or a small metal file and clean up the inside of the connector.
Usually, a minute or two of cleaning should be enough. To make this a little easier, you can give the inside of the connector a quick spray of WD-40 contact cleaner to break down any corrosion and grime.
So, once you have cleaned out the connector, give your weed eater a try. Hopefully, this will fix the issue. But, if you are still having problems and you’re unable to restore the connection, then you’ll need to replace the coil.
Unfortunately, weed eater coils are usually sealed units, and you can’t just replace the cable. So, if this is the case with your weed eater, you can read below about how to completely replace a weed eater coil.
Tools to Repair a Weed Eater Spark Plug & Cable Connection
- Small Metal File
- Sandpaper
- WD-40 Contact Cleaner
Gapping the Coil & Magnet
To correctly gap your ignition coil and the flywheel magnet, start by turning the flywheel so that the magnet and coil are not inline. Then, take a screwdriver or nut driver, depending on your weed eater, and loosen off the coils mounting bolts.
Next, place your feeler gauge between the coil and the flywheel, remembering to use a feeler gauge thickness specific to your weed eater. Now, turn the flywheel until the magnet and coil line up. The magnet’s power should attract the coil and close the gap between the two components.
Finally, tighten the two coil mounting bolts and remove the feeler gauge. So, by having the feeler gauge in place while the coil and magnet are pulled against each other, the gap should close to the specific gap you need.
Tools to Set the Coil & Magnet Gap
- Screwdriver
- Nutdriver
- Feeler Gauge
Removing Coil Corrosion
To remove the corrosion from the coil armature and the flywheel magnet, you’ll first need to remove the coil from your weed eater. So, use either a screwdriver or a nut driver to remove the two mounting bolts from the coil.
Then, use fine-grit sandpaper, such as 220-grit sandpaper, to lightly sand both surfaces of the magnet and the coil armatures. Your aim is to remove the corrosion and not sand off any of the metal from the two components. Removing metal would cause unnecessary wear and reduce the life span of both the flywheel magnet and the coil.
So, once you have the two parts cleaned up, reinstall the coil back onto your weed eater and reset the coil gaps using the steps for gapping the coil & magnet from above.
Tools to Remove Coil Corrosion
- Screwdriver
- Nut Driver
- Fine Grit Sandpaper
Replacing a Weed Eater Coil
To replace your weed eater coil, you’ll first need to remove the engine cover of your weed eater to gain access to the engine. So, using a screwdriver or a nut driver, remove all the fixings that secure the cover to the engine. Then, lift the cover off your weed eater.
Next, remove the cable from the spark plug and the small ground wire from the coil. Then, using your screwdriver or nut driver, remove the bolts that secure the coil to the engine and lift the old coil off your weed eater.
Next, position your new coil onto your weed eater’s engine, followed by loosely installing the coil mounting bolts. Then connect the small ground wire to the new coil and connect the cable to the spark plug.
Now, all that is left to do is gap the new coil using the same steps as before. Finally, reinstall the engine cover, and you are ready to go.
Tools & Parts to Install a New Weed Eater Coil
- Screwdriver
- Nut Driver
- Feeler Gauge
- Replacement Coil Specific to the Engine
Replacing the Weed Eater Kill Switch
Depending on your specific weed eater, you may or may not be able to purchase a replacement switch by itself without buying a complete assembly. For example, Stihl allows you to buy a replacement kill switch with the wires attached without having to purchase the entire handle assembly. So, let’s take a look at how to install a replacement kill switch for a Stihl weed eater like the FS-45 and the FS-50.
First, use a screwdriver to remove the screw from the throttle assembly located on the main shaft of the weed eater. Then, lift off the loose side of the throttle assembly to expose the kill switch.
Next, remove the mounting bolts from the engine cover to gain access to the engine. Now, locate the wires from the kill switch connected to the engine/coil and disconnect the connectors. Next, lift the old kill switch out of the weed eater handle and pull the two cables out of the plastic protective sleeve going to the engine. Once you have the cables free, you can set the old kill switch to one side.
Now, grab your new kill switch and thread the two wires through the plastic sleeving. Then, connect the wires to the engine and coil. Then once you have the wires attached, it’s time to install the switch into the handle assembly. So, slot the new switch into the position and make sure that it is secure.
Next, try the switch and make sure it is turning on/off without any problems. Sometimes, you’ll need to line up the outer switch button on the handle with the new switch, as these two parts are separate. So, once you have confirmed that the switch is operating correctly, you can go ahead and reassemble the throttle housing and reinstall the engine cover.
Once this is complete, your weed eater should no longer have an issue with a permanent coil ground, and your weed eater should work fine.
Tools & Parts to Replace a Weed Eater Kill Switch
- Screwdriver
- Nutdriver
- Replacement Kill Switch
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