Weed Eater Spark Plug: 10 Things You Should Know

The weed eater spark plug is a small engine component that can make a big difference in the way your weed eater performs. The spark plug is an essential part of your weed eater that is positioned on the engine housing. Without it, the engine would not start, and you would be left with a lawn full of weeds! Weed eater spark plugs are a common replacement part for your weed eater.

After realizing a lot of gardeners have holes in their knowledge where tool maintenance is concerned, I’ve put together a guide to understanding a weed eater spark plug. Here are 10 things you should know about it.

It should be noted only gas-powered trimmers need a spark plug. If you’ve got a battery-powered or electric weed eater, it’s just the battery and/or plug that needs maintaining.

How To Know If Your Weed Eater Needs A New Spark Plug

Not all weed eaters need a spark plug. Battery and electric versions don’t contain liquid fuel, so they don’t need an igniter. But gas-powered tools depend on them. Without a working spark plug, your weed eater won’t start, or it will stop-start in a sputtering fashion. The good news is spark plugs are cheap, widely available and easy to replace.

Here is a quick way to check if your weed eater’s spark plug is functional.

First, remove the plastic covering to expose the spark plug. Remove the boot protector. Use a socket wrench to unscrew the spark plug. Carefully lift it out and look for the following signs:

• Black carbon deposits on the spark plug and/or plug terminals
• An overly wide gap between the terminals and spark plug gauge
• Any visible corrosion or degradation of the spark plug

Any of these signs can be a clue as to why your weed eater spark plug isn’t functioning correctly. I recommend dealing with them one by one until you find the right solution. If you address all three and the spark plug still doesn’t work correctly, you probably need a replacement.

I’ll explore each of these issues and how to fix them a little later. For now, let’s familiarize ourselves with what a spark plug looks like and where to find it on your weed eater.

Do Weed Eaters Take Spark Plugs

We’ve established that gas-powered weed eaters need a spark plug to function. These components are pretty small, normally around 16mm in length. Their job is to generate an electrical spark to ignite the combustion that fuels the device. It’s not too different from a car engine. There’s got to be a spark to bring the machine to life.

If the spark plug stops firing or struggles to fire, your weed eater won’t have enough energy to stay on. That’s the basic explanation. Now, if you’re feeling curious, let’s get technical.

The spark plug produces a burst of electrical energy which jumps across the gaps in its firing end. If it’s not in good enough condition or it’s over-fouled, its voltage might be too weak to bridge the space.

When an electrical spark reaches an ignition coil or magneto, electrons are released, and a voltage difference develops between the central and side electrodes. At first, the spark is impeded. No current can travel across the gap and connect the terminals because a combustible mixture of gas and air acts as a barrier.

However, as the voltage increases, the structure of this barrier begins to change, and the gas becomes ionized. It is now a conductor, and the electrons start to flow freely between the terminals. This significantly increases the temperature of the spark channel.

The sudden burst of thermal energy causes the ionized gas to expand much like a miniature explosion. Listen carefully and you can hear a ‘click’ sound when this happens.

The result is an intense, contained flame that acts as an igniter and turns the weed eater on. Crucially, the spark plug is also capable of regulating thermal energy in the combustion container.

It draws unwanted heat away from the combustible materials and channels it to the device’s cooling components to be neutralized. This is a really important function because, otherwise, your weed eater might heat up in summer or an overly hot garage and switch itself on.

Think of the weed eater spark plug as the first domino in a chain. It launches the ignition process but it can only complete it if all the components are positioned correctly.

If the spark plug is covered in carbon deposits or the gauge or terminals are misaligned, the chain is severed. Most spark plugs require a voltage of at least 20,000v to ignite efficiently.

How To Tell If A Weed Eater Spark Plug Is Bad

The quickest way to tell if your weed eater’s spark plug is misfiring is to remove it and take a close look at it.

So, you need to locate the crankcase first. The crankcase is a protective plate that conceals the spark plug. It should be easy to lift with a fingernail.

1 – Use your fingernail to lift the cover and reveal the spark plug and spark plug wire.

2 – Remove the boot protector. This is a small rubber cap that fits over the spark plug and protects it from debris and contaminants.

3 – Give the area around the plug a quick wipe to remove any debris. Bits of dust, dirt and other materials mustn’t inside the weed eater’s fuel compartment.

4 – Use a ratchet and a spark plug socket (normally a 5/8-inch socket) to remove the spark plug from the weed eater.

5 – When I remove a spark plug from a device, I plug the hole it leaves with a clean rag. This prevents bits and pieces of debris from dropping into the combustion chamber and causing problems later. I recommend you also take this precaution.

6 – Inspect the spark plug for black carbon deposits. While it’s normal for some degree of staining to accumulate over time, these deposits can build up and prevent a weed eater’s internal components from connecting and this may cause misfires. If the spark plug is heavily stained, the fuel is probably too rich.

7 – To remove the carbon deposits, gently abrade them with an emery board taking care not to apply too much force. Take a close look at the spark plug’s terminals. If they have carbon deposits too, remove them by running the emery board across the surfaces where sparking occurs. Use a fingertip to identify any areas that are extra rough and built up with carbon.

8 – Turn your attention to the space between the plug’s terminals. You’ll need a spark plug gauge or a similar-sized tool to measure the small gap. If it measures more or less than 0.030 inches, use fine-nosed pliers to adjust it.

9 – Test whether these adjustments have improved your weed eater’s firing capabilities by putting the boot protector on and tapping the plug on a metal part of the engine. Pull the device’s starting cord as you do this. If it’s firing correctly, you should see a blue spark jump between the terminals every time the cord is pulled.

10 – If you’re having trouble with the previous step, an alternative test is to wind a piece of 14-gauge copper wire around the plug’s threads. Tap the end of the wire on a metal part of the engine and watch for a blue spark.

11 – A healthy spark is a clear blue color. If your spark is very pale or yellow, take another look at the gap between the terminals. This often happens when the gap has become too wide and needs some adjusting. The opposite is true – the gap between the terminals needs to be widened – if the spark doesn’t stay between the terminals but jumps to a different part of the spark plug’s head.

12 – Repeat steps nine and/or ten to see if your adjustments have worked. If the gap between the terminals is now optimal but the spark continues to be weak or inconsistent, it’s time to get a new one. The spark plug should be replaced.

What Kind Of Spark Plug Do I Need For A Weed Eater

If your weed eater spark plug is not firing correctly and needs replacing, you have a lot of options.

There are several leading brands to choose from including Husqvarna, Ryobi and Homelite. It’s up to you to decide whether the same brand or a completely different brand of spark plug is the best choice.

Always check your weed eater’s specs before buying new components to guarantee compatibility.

Some specialist machines will need a specific type of spark plug that is only available from one brand. The vast majority though are compatible with any brand provided a plug’s dimensions and heat range are suitable.

There’s no reason you can’t replace a misfiring spark plug with a new one from a different brand. It’s not like your weed eater’s engine can tell the difference.

Here are some weed eater and spark plug combos that I’ve tried and loved:

Best Spark Plug For Stihl Weed Eaters – NGK Iridium IX Spark Plug

Last update on 2024-04-19 / Affiliate links / Images from Amazon Product Advertising API

Pros

• Impressive fuel efficiency
• Iridium for extra strength and durability
• Lasts up to 25% longer than platinum plugs
• Needs less voltage to fire successfully

Cons

• Iridium makes this spark plug pricey
• Slightly higher risk of flammable dust

Best Spark Plug For Troy Bilt Weed Eaters – Champion 810 Spark Plug

Last update on 2024-04-19 / Affiliate links / Images from Amazon Product Advertising API

Pros

• Trusted OEM for many small engines
• Great value for money (low cost, high quality)
• Patented RFI and EMI suppression
• Commonly sold in twos (two plugs, one price)

Cons

• Not all versions have a copper finish

Best Spark Plug For Echo Weed Eaters – Autolite Iridium XP Spark Plug

Last update on 2024-04-19 / Affiliate links / Images from Amazon Product Advertising API

Pros

• Iridium enhanced for strength and longevity
• Increased ignitability (smoother firing)
• Broad compatibility with gardening tools
• Price is reasonable (for an iridium tip)

Cons

• Almost always sold in four-packs
• Iridium dust is more flammable

Best Spark Plug For Ryobi Weed Eaters – Bosch Platinum +4 Spark Plug

Pros

• Trusted mainstream brand
• Groundbreaking surface air gap firing tech
• Contains 4 yttrium enhanced electrodes
• Superior ignitability and heat transfer

Cons

• Yttrium components can be pricey
• Slender/fragile terminals

Best Spark Plug For Craftsman Weed Eaters – E3 Powersports Spark Plug

Last update on 2024-04-19 / Affiliate links / Images from Amazon Product Advertising API

Pros

• Built to withstand cold temperatures
• Yttrium enhanced alloy for durability
• Good for heavy-duty use
• New design reduces emissions

Cons

• Price can vary a lot
• Smaller performance boost than other plugs

Best Spark Plug For Husqvarna Weed Eaters – Bosch 7547 (WSR6F) Spark Plug

Last update on 2024-04-19 / Affiliate links / Images from Amazon Product Advertising API

Pros

• Anti-corrosion nickel-plated threads
• Great for cold weather starts
• Nickel chromium electrode increases ignitability
• 5-rib insulator reduces flashover (fewer carbon deposits)

Cons

• Reported to wear faster than some others
• Not compatible with as many tools

Best Spark Plug For Toro Weed Eaters – NGK Ruthenium HX Spark Plug

Last update on 2024-04-19 / Affiliate links / Images from Amazon Product Advertising API

Pros

• Easily one of the best on the market
• More complete/consistent fuel burn
• Extremely long-lasting
• Superior oxidation resistance

Cons

• Can be very, very expensive
• May be overkill for a lightweight weed eater

Best Spark Plug For Homelite Weed Eaters – Champion Copper Plus Spark Plug

Last update on 2024-04-19 / Affiliate links / Images from Amazon Product Advertising API

Pros

• Very good value for money
• Ideal for lightweight gardening tools
• Corrosion-resistant body
• Copper core for durability

Cons

• Low price means less longevity
• May not be suitable for heavy-duty tools

How To Remove A Spark Plug From A Weed Eater

Though every weed eater model is slightly different with its own unique features, generally speaking, these tools follow the same basic design structure. There’s a long thin pole with a cutting head at the bottom and a handle and a small engine at the top.

The quickest way to learn how to remove a weed eater spark plug is to consult the manufacturer’s instructions. But if like me, you rarely keep track of where you put your tool guides, you can work it out with a bit of twisting and turning.

Here is my advice on how to do it. Don’t worry if the steps don’t always match up perfectly. If you get stuck, just take a close look at your weed eater to identify its components and compartments.

You’ll need a spark plug socket and wrench to get started.

1 – Use your nail to lift the protective cover and reveal the spark plug in its housing.

2 – Locate the boot protector boot that fits over the spark plug to protect it from debris and contaminants. Some are rectangular. Others are tubular. Identify the spark plug wire.

3 – Using a flat-head screwdriver (if necessary), gently lever the boot protector off the plug. If you meet resistance because the boot seems to be stuck to the spark plug, don’t tug. Pry upwards with the screwdriver at the same time as you’re pulling the boot off with your other hand. Giving the boot a gentle side-to-side wiggle can help to loosen its grip on the plug.

4 – Apply the spark plug socket over the top of the spark plug. Most weed eaters need a 5/8- inch socket but some others work with a 3/4- or 13/16-inch socket and wrench instead. It depends on the model you’re using.

5 – Attach the socket wrench and turn counterclockwise to loosen the plug. You can switch to using your fingers once the spark plug is turning with ease. Carefully lift it out, and viola, your spark plug is ready to be inspected and/or replaced.

Tips for removing a Spark Plug Quickly and Safely

• Position the weed eater horizontally for easy access
• Stand as far away from the cutting head as possible
• Always pull on the plug and never the spark plug’s wire
• Clean surrounding areas of dirt and debris as you work
• To get a good grip with the wrench, hit it gently with your palm
• If necessary, spray a little WD40 around the plug to lubricate it

Weed Eater Spark Plug Size

Weed eaters and other gas-powered gardening tools like edgers and trimmers use a 3/4- inch spark plug, which is the standard size. Most weed eater spark plugs are this length, but you should still look at the manufacturer’s instructions before buying a replacement plug for your device.

Spark plugs do come in a variety of sizes but only a few are designed for small engines. Something as long as a 14mm spark plug is better suited to a car or motorcycle than the lightweight engine on a string trimmer.

Here are some common spark plug sizes:

• 14mm – primarily used in cars and motorcycles (contemporary European/Asian)
• 9/16- inch – most common type of spark plug for Ford engines
• 5/8- inch – common in GMC, Nissan, Subaru, Chevy, Koehler and Briggs and Stratton engines
• 11/16- inch – most often seen in older BMW engines
• 18mm – common option for smaller motorcycles and other small engines
• 3/4- inch – designed for use in lawnmowers, weed eaters, trimmers, edgers, etc.
• 13/16- inch – better suited to larger engines in older, heavy-duty vehicles
• 7/8- inch – usually seen in large farming machines like tractors, some older cars and some aviation vehicles

Shopping for a new weed eater spark plug can be confusing if you’re not familiar with the common sizing standards. Most engine manufacturers produce five or six different sizes but only one or two of these will be suitable for your gardening tool.

If you are browsing for a replacement, do a Google search for the year, manufacturer and type of engine to get information on the optimal spark plug size.

For example, you might search “2017 Stihl 1.5L spark plug size” to identify the best spark plug for your needs.

Alternatively, remove the old weed eater spark plug and measure it to find out what size to replace it with. Once removed, measure right from the center of the tapered edge (just above the threads) to the bottommost thread. This will give you the spark plug’s length. Measure across the threads to get the plug’s diameter.

Weed Eater Spark Plug Gap

The spark plug in a weed eater’s engine won’t fire correctly unless the space between its ground and center electrodes is precisely the right size. This is a distance of 0.030 inches for most weed eaters. If the gap between the electrodes gets any wider or narrower due to normal jostling and movement, the engine might struggle to ignite.

Fortunately, it’s easy to adjust a spark plug’s terminals and make the gap a little bigger or smaller as required. Over the years, I’ve reminded plenty of friends and neighbors to measure the gap in a spark plug and see if they can fix a weed eater themselves before going out and buying a new one.

All you need to ‘gap a spark plug’ is a pair of fine-nosed pliers and a spark plug gauge (sometimes called a feeler). The finer the points the better because we’re talking about very small components.

You’ve got to keep a steady hand but all you’re attempting to do is create a gap of precisely 0.030 inches by bending the ground electrode inwards or further away from the center electrode.

So, use your gauge to measure the existing gap in the plug first. If it is more or less than 0.030-inches, it might be the reason your weed eater isn’t firing correctly or at all. Work out if you need to pull the electrodes closer together or further away to remedy the problem.

Dealing With The Gap In Brand New Spark Plugs

You shouldn’t need to recalibrate or adjust the gap in a new spark plug. A new component should arrive in perfect condition, ready to be fired. I say ‘should’ because it doesn’t always happen this way.

Replacement spark plugs get bumped around in the mail all the time. Or a weed eater spark plug you think is a perfect fit might turn out to be calibrated for a slightly different engine.

It happens, and it’s useful to know how to identify and fix the problem. If you order a replacement spark plug and it seems to be faulty right out of the box, take a look at the gap before getting on the phone to customer service. It could be fixed in a couple of minutes.

1 – It’s worth inspecting your weed eater spark plug for carbon deposits and other debris while you’re fiddling around with it. If any dirt or material gets inside the engine’s combustion chamber, it could cause irreparable damage to the components. So, if you have one handy, clean around the plug with a wire brush before you remove it.

2 – Use the spark plug gauge to measure the gap between the electrodes. This is easy to do once you’ve set the optimal measurement on the gauge. If the gap is the correct size, you should be able to slot the gauge inside it so that it’s touching both electrodes. If you have to force it, the gap is probably too small.

3 – Determine if the gap in your plug is too wide or too narrow. An overly narrow gap risks a weak spark that cannot jump between electrodes and ignite the engine. An overly wide gap may be too much of a distance for the spark to jump. Your weed eater might fire sometimes and sputter and fail at others. Using the needle-nose pliers, make adjustments as required.

How Often To Change A Weed Eater Spark Plug

The rule of thumb for swapping out weed eater spark plugs is to replace them after a hundred hours of use. Advice varies depending on the model and its manufacturer so consult the handbook or guide if you have it. If you don’t, you should at least aim to check your plug’s condition every hundred hours or so.

As a spark plug ages, the gap between its electrodes starts to widen. You can remedy this for a while by recalibrating the gap yourself but, in time, the metal parts will begin to erode.

The edges of the two electrodes will become ‘fuzzy’ and rounded and lose their clean lines. This further increases the gap until you’re left with a spark plug that needs constant calibration. At this point, it’s time to buy a replacement.

This gradual aging and widening is the reason a lot of mechanics calibrate the gap on new spark plugs to a minimum workable distance. They want to give the plug as much space to widen within its operational limits as possible.

One hundred hours is the recommended lifespan of a weed eater spark plug but it’s not uncommon for tools to last much longer than this.

Longevity is affected by a range of factors such as the terrain being trimmed, climate and seasonal temperatures and even the type of metals used in the component.

So check on your spark plug often. A quick look can tell you all kinds of things about its health and performance.

How To Clean A Weed Eater Spark Plug

We’ve talked about recalibrating the gap inside your spark plug. We’ve discussed the best method and timeframe for replacing a weed eater’s spark plug. What if your spark plug is relatively young and healthy but it has developed a build-up of grime and carbon that’s weakening its firing power?

This is a common problem with a simple solution. There’s no hard and fast rule for cleaning spark plugs. It’s at the discretion of the user and depends on how often the weed eater is operated, whether it’s regularly pushed hard on rough terrain and whether it’s well maintained and stored correctly.

The easiest way to tell if a spark plug needs cleaning is to remove and inspect it.

Fouled spark plugs are covered in black carbon stains that can be sooty, crusty or both. Over time, these deposits can build up, getting rougher and crustier until they start to impede the spark as it crosses the plug’s electrodes.

This may lead to weak, inconsistent firing or firing failures. You can use WD40 to loosen light fouling on a spark plug but cover up any holes leading to the combustion container before you spray.

If the fouling is stubborn, use an emery board or even a piece of fine sandpaper (180 or higher) to gently abrade the stains.

1 – Using a nail file or piece of fine sandpaper, rub the stains with a light-handed motion. If possible, do this on a flat surface with the spark plug positioned away from the combustion chamber. You don’t want any debris to fall in.

2 – With the same light-handed motion, slide the file between the arm and the electrode. Rub gently to loosen any carbon deposits. You may need to cut a piece of sandpaper into small pieces for this.

3 – Slide the file or sandpaper between the white insulator and the electrode to remove any debris that is trapped in the small channel.

4 – Once finished, use an air hose (or a regular drinking straw) to blow any fine pieces of dust and debris away from the de-fouled plug. For safety reasons, you should close your eyes. It hurts to get tiny pieces of metal in your eyes, trust me.

PLEASE NOTE – You should not use any type of file or sandpaper on an iridium tip or component as you can damage the metal.

Helpful Tips To Know About Weed Eater Spark Plugs

• NEVER submerge a spark plug in water to clean it or for any other reason. You could cause irreparable damage.
• If your spark plug gets fouled soon after you’ve cleaned it, the type of fuel you’re using might be too rich. Some degree of fouling is normal but a weed eater spark plug that’s constantly covered in grime may indicate a problem. The engine’s air-fuel mixture may be too rich, its ignition might be firing inconsistently, or it may be struggling with cold temperatures.
• Only remove one spark plug at a time to avoid confusion and incorrect wiring.
• A general rule of thumb is to replace (or at least inspect) your weed eater’s spark plug once every hundred hours.
• Some symptoms of a faulty spark plug include failure to start, inconsistent starting (it fires sometimes but not all the time) and excessive emissions and/or vibrations.
• Do not file or use sandpaper on spark plugs with iridium tips.

Final Thoughts

I’ve covered a lot of different types of spark plug maintenance in this guide. Hopefully, you’re prepared for the next time your weed eater spark plug develops a fault or begins to behave unpredictably. Indeed, some faults can’t be fixed, and a replacement plug is the only solution. However, applying these skills can help extend your plug’s lifespan.