How To Tell If Your Weed Eater Spark Plug Is Bad

weed eater plug

Just like a car engine, gas-powered weed eaters need spark plugs to fuel them. And, similar to a car engine, they can also misfire or “go bad,” which can make your weed eater impossible to use. But how do you tell if a weed eater spark plug is bad or needs replacing? When it comes to diagnosing and troubleshooting a bad spark plug on your weed eater, here’s what you should know. 

How To Tell If a Weed Eater Spark Plug Is Bad

A spark plug that’s misfiring or malfunctioning can cause problems in a couple of different areas. 

Engine Won’t Start or Runs Poorly

Your weed eater’s small engine relies on a spark plug to produce an electric spark that ignites the gas in the combustion chamber. If there’s a lot of carbon buildup in the ignition chamber, which can happen over time with two-stroke engines, or if the gasoline and oil don’t get mixed correctly, your weed eater’s engine might feel less powerful, have trouble starting, or not even start at all. 

Since spark plug issues can happen over time, your engine may not just suddenly die – but over time, it may run more and more poorly until you’re not able to start it at all. 

There is an exception to this. If the ceramic cracks or deforms on your spark plug, your engine could die suddenly, and you may not be able to start your weed eater again until you replace the spark plug

High Fuel Consumption

Does it seem like your weed eater is constantly low on gas, even though you fill it up just as much before? Does it seem like it’s about to die even though you’ve just put gas in it? While high fuel consumption on a weed eater could mean a couple of different problems – like not mixing the correct ratio of gas and oil – it could also be because of a malfunctioning spark plug. 

This sign of a bad spark plug usually shows in combination with your weed eater not starting or running poorly. 

Inspect The Spark Plug

One of the easiest ways to tell if you’ve got a bad spark plug is just by looking at it. Not all malfunctioning spark plugs may have visible evidence that they’re bad, but many of them do. 

To inspect the plug, here’s a quick guide on how to do so: 

  • Look for the crankcase. Your spark plug will be in your crankcase, which is the protective plate that houses the plug, and it should be easy to lift without any additional tools.
  • Next, you’ll need to remove the boot protector, the small rubber cap that keeps your spark plug safe from excess debris.
  • Once you’ve lifted the crankcase and removed the boot protector, you can use a ratchet and socket wrench to unscrew the plug.

While you’re trying to remove and inspect the spark plug, it’s important that contaminants and debris don’t fall into the fuel compartment. Make sure you wipe off the spark plug but also plug the hole into the fuel compartment with a rag so that debris doesn’t get in. 

What Does a Bad Spark Plug Look Like?

Now that you’re inspecting your string trimmer spark plug, what does a bad spark plug actually look like? There are a couple of ways to diagnose a malfunctioning spark plug based on appearance, including: 

  • Look for black carbon deposits. While it’s natural for some staining to occur over time, black carbon deposits can happen from too much carbon buildup, and it can mean your spark plug is misfiring. A lot of staining could also signal that you’re not mixing your gas and oil correctly, and the fuel is too rich.
  • Inspect the spaces between the spark plug’s terminals with a spark plug gauge. If the space is more than 0.030 inches, then the gap is too wide and it needs to be readjusted. You can either readjust with needle-nose pliers or just replace the plug.
  • Check for corrosion and cracks on the plug. Even if the gaps between terminals are fine and there are no carbon deposits, the plug could be cracked or corroding. A good spark plug is usually a healthy blue color, so if it’s corroded, it may turn close to pale yellow or white. 

Remember – Only Gas Weed Whackers Have Spark Plugs

Keep in mind that the spark plug can only be a problem on your weed eater if it actually has one  – and only gas-powered weed wackers do. If you’re using an electrical or battery-powered weed eater, your weed wacker is experiencing a different issue, like the carburetor, exhaust system, or choke valve. 

How To Clean a Weed Eater Spark Plug

Sometimes just cleaning a spark plug could make a big difference in your string trimmer’s power, especially if the plug seems heavily stained. To get rid of the stains, the best method is usually a piece of sandpaper or emery board, and here’s what to do: 

  • Place your spark plug on a flat surface that’s away from the combustion chamber. Using your sandpaper, gently rub the stains with light motions. 
  • To get rid of stubborn carbon deposits, you can use your sandpaper (which you can cut into smaller pieces) or your emery board to slide the paper in-between the electrode and the arm. This process will help loosen those carbon deposits. 
  • Next, remove any debris between the electrode and the white insulator by sliding your sandpaper into the channel. 
  • Since the sandpaper or emery board has helped loosen debris and deposits, the final step is to take an air hose or drinking straw to blow the debris completely off the plug. Make sure you’re using safety goggles while you do so. 

How Often Do I Need to Change Spark Plugs?

As a general rule, you should change your spark plugs after 100 hours of use, although the number can vary based on model and brand. You can check your owner’s manual or the manufacturer’s website for more specific information about your model. 

Helpful Tips About String Trimmer Spark Plugs

When it comes to cleaning, maintaining, or dealing with spark plugs, here are a few helpful tips to keep in mind: 

  • Never put your sandpaper or emery board on the iridium component of your spark plug as this could damage the metal and plug.
  • If your weed eater uses more than one spark plug (which many don’t), make sure you’re only removing and cleaning one at a time.
  • If you’re cleaning your spark plug regularly and it’s always covered in grime, there’s most likely an issue with the ratio of oil and gas.
  • You should never place your spark plug in water or try to clean it with soap and water as this could damage the plug beyond repair.

Spark plugs are a crucial part of any weed eater’s mechanics, and a faulty one could make a huge difference with how your weed wacker performs on your lawn and garden. If you’ve got more questions or concerns about whether a spark plug is bad, be sure to comment below! 

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