Do Weed Eaters Have Spark Plugs?

If you have encountered problems with your weed eater, one of the first things you check is the spark plug. But what exactly does a spark plug do, and is it required for all weed eaters? I’m going to answer that question here along with other things you need to know about spark plugs.

Gas weed eaters have spark plugs because it supplies the spark needed to ignite an engine. This allows air and fuel to mix, leading to combustion. Without a spark plug, gas wed eaters cannot run.

Why Weed Eaters Need Spark Plugs

Whether it is a string trimmer, lawn mower or another small engine, the spark plug plays the same role. It is literally the spark that gives life to the engine. It generates the power that leads to ignition.

Once ignition starts, the carburetor mixes the air and fuel. This results in a combustion, powering the engine and your weed eater. This video shows you how a spark plug works. The principles in this video apply to all kinds of small engines including weed eaters and trimmers.

All of this takes place in a matter of seconds or less. If you have ever used a gas string trimmer like the Lawn Master 25cc, we usually don’t give this process much thought. We just turn it on, pull the cord and start trimming. But there’s a lot going on to get the engine going.

A faulty spark plug causes all kinds of problems for the engine. If it’s new but your string trimmer refuses to run, check out this guide on why weed eaters won’t stay running.

if the spark plug isn’t working, clean or replace it immediately. And this brings us to the next important topic.

Are Spark Plugs Interchangeable?

Weed eater spark plugs are not interchangeable. You have to use one that is compatible with your string trimmer.

Check your string trimmer instructions to find out what spark plug you need. While these components look similar, they have different specifications. Use the wrong spark plug and your weed eater will not run. Worse it can cause engine problems.

If you no longer have the manual, go to the brand website and look for spark plugs that are compatible your make and model.

It’s easy to imagine that spark plugs are universal because they look alike. But that’s not the case. If you check small engine spark plug requirements, it lists specific types.

If you use a non-compatible spark plug, it can lead to serious or permanent damage. That’s why you have to be thorough and use only those components with the right specifications.

Features to Look for in a Weed Eater Spark Plug

If you have to replace the spark plug, there are some specific features you have to consider. I have listed down the most important below. As always you should look into the manual.

Size. Most string trimmers accept spark plugs up to .75 inch. This is the maximum size, and some trimmers might work with something smaller.

Gap. This the space between the center and ground electrodes. The gap has to be 0.03 inches. If the gap is off by even a fraction, the engine won’t run. This shouldn’t be a problem though as all string trimmer spark plugs are set to this.

Temperature. String trimmer spark plugs must be able to run between 932-1472 F. It’s not surprising though because spark plugs are responsible for ignition and engine combustion.

Material. Spark plug electrodes are made from various materials including platinum, iridium and copper. From personal experience I’d say that copper electrodes will work just fine.

When to Replace Weed Eater Spark Plugs

Replace the spark plug after 30 hours of use or before the start of each season. There are a few things I want to add here though.

The 25-30 hour replacement is for general guidance only. This is based on the assumption that you use the weed trimmer “normally” and have an average sized lawn. In this case, a spark plug will last for 30 hours or so.

If you trim weeds more often, you’ll need to replace the spark plug faster. How quickly depends on how much work the trimmer gets.

Bottom line: the 25-30 hour guideline is just a guideline. If the spark plug is bent, cracked or dirty, replace it now.

You are probably also asking if spark plugs are reusable. Yes, but it’s better to just replace it. Spark plugs are cheap and easy to replace. It isn’t worth the effort to clean a spark plug as it won’t be as good as before. It is better to just replace it.

How to Replace a Weed Eater Spark Plug

There are many types of weed eaters, but spark plugs are replaced the same way. Before proceeding, make sure you have a compatible replacement spark plug in hand.

Place the weed eater on an even surface, outdoors and well ventilated.

Look for the spark plug wire. In some models it looks like a rubber boot that holds the plug and wire. Other string trimmers come with a tubular boot instead. Refer to the user manual if you’re not sure.

Get a flat head screwdriver and set it against the boot. With your free hand, pull the boot up. Keep pulling until the boot comes off.

Use a socket wrench to remove the spark plug. A 3/8 size works fine in most cases but look in the instructions to be sure.

Turn the wrench counterclockwise until the plug loosens. Remove the spark plug.

Install the new spark plug. Reconnect the spark plug wire.

Signs of a Bad String Trimmer Spark Plug

The most common symptoms of a broken spark plug are cracks, carbon deposits and corrosion. If the gap between the terminals is more than 0.030 inches, you have to narrow it or get a replacement.

Black carbon deposits can cause the spark plug to malfunction. This can happen through heavy use, wear and tear or the fuel is too rich. If the spark plug builds up carbon deposits quickly, check the fuel mixture.

Aside from the physical characteristics, there are other indications the spark plug is not working.

Wed eater is slow or unresponsive. There are many reasons why this can happen but a malfunctioning spark plug is near the top of the list. The spark plug is connected to engine ignition and fuel combustion, so any malfunction is going to affect performance.

Runs out of fuel fast. A faulty spark plug requires more fuel to function. If your string trimmer is using more fuel than before, it’s a good idea to check the spark plug. The fuel mixture might be too rich so the engine consumes more than usual.

Engine starts and stops. A surging engine is another indication the spark plug isn’t working. Whether it is due to carbon deposits, physical damage etc. the engine is forced to consume more air during the combustion process. This isn’t how string trimmers are supposed to work

Engine refuses to start. There are a lot of reasons this can happen, but the spark plug is a good place to look.

Frequently Asked Questions

Do all string trimmers have spark plugs?

Only gas weed eaters have spark plugs. Corded and cordless string trimmers don’t need it.

Spark plugs are used to to ignite the fuel and start the engine. Electric string trimmers like the Black and Decker do not need fuel. They rely on electricity so a spark plug is not required. This also applies to cordless or battery powered string trimmers.

Is it possible to test a string trimmer spark plug?

Yes. There are spark plug testers available, similar to the ones you use on a car. It’s a good idea to have one in case you want to make sure the spark plug needs to be replaced.