8 Reasons Why a Weed Eater Won’t Start

A weed eater is a brand of string trimmer whose name has caught on and stuck with owners for over four decades.

Most have two-cycle engines, but there are some manufacturers who offer four-cycle varieties. 

They are prized for their torque and ability to chew through tough weeds and a light brush while also being able to clean up the little tufts of grass left behind by the lawnmower.

A lawn without a weed eater tends to look unkempt as grass continues to grow unchecked around trees and landscaping.

When your weed eater dies, it’s sure to bring a groan of frustration. This might also leave you wondering if there’s anything you can do when your weed eater won’t start.

Of course, there’s no single right answer as to what might be causing the problem. The following tips can help you fix a weed eater that won’t start.

In many of these cases, some simple tools and a little mechanical sympathy might just be able to bring your trusted string trimmer back to life.

Reasons Why a Weed Eater Won’t Start

Your weed eater won’t start or stay running? Any of these issues could be to blame:

• Fuel Issues
• A Clogged Fuel Filter
• ​Dirty Air Filters
• Bad Spark Plug
• Carburetor Covered In Sludge
• A Flooded Engine
• Problems with the recoil
• Battery failure

What to do to troubleshoot the issue depends on the source of the malfunction. Keep reading to learn more about the various possible causes that could prevent your weed eater from starting and how to fix them. 

Just like the lawnmower, your weed eater and other gas-powered equipment need some routine maintenance when you put them away for the winter.

It also needs some extra care in the spring to help bring it back to life. If you have a large yard with a lot of complicated landscaping your weed eater might need in-season oil changes and other maintenance measures to prevent starting issues.

In the winter, you need to put a fuel stabilizer in the fuel tank. Without the special stabilization component, the fuel’s octane can start to degrade, and water can start to separate from the gasoline.

To be safe, I like to leave the tank half full, so there’s enough headroom in the spring for some fresh gas.

In the spring, fresh fuel ensures that the engine has a high enough level of octane available to fire up and stay running at high revs.

If it’s a two-cycle, you also need to make sure that the mix ratio of the oil in the new fuel is correct.

If you have a four-cycle weed eater, you should change the oil every spring.

While you are at it, clean or replace the air filter, and look for any other maintenance items, like the fuel filter, spark plug, or any sections of the string that look brittle and worn.

If you have a new spool of string available, I would recommend replacing it.

1. Fuel Issues Can Prevent A Weed Eater From Starting Or Staying Running

Clean, reliable fuel is absolutely essential for a properly functioning weed eater.

Most have a two-cycle engine, which means you need to premix the correct type of two-cycle oil for an air-cooled engine.

If the ratio is too rich, meaning there is too much oil in the tank, it can make it difficult for the spark to ignite the fuel in the combustion chamber, which might prevent your weed eater from starting.

If you stored the weed eater away in the winter without a fuel stabilizer in the gas tank, the fuel may have degraded, or water has separated out.

In a situation like this, you can add Iso-Heat or a similar fuel conditioner. If you don’t have any on hand, you can always drain or siphon out the old fuel and replace it with fresh, premium gasoline.

If you suspect that you mixed the fuel wrong, you should siphon or drain the tank to troubleshoot the issue.

2. A Clogged Fuel Filter can Prevent A Weed Eater From Starting

Some weed eaters have the fuel filter installed in the fuel line, some have it inside the fuel tank.

If debris or residue from old fuel has entered the fuel filter, it could be so clogged that fresh fuel simply cannot reach the combustion chamber which can prevent your weed eater to start again.

If your fuel filter is inside the fuel tank, you will likely need professional service. If you can get to the fuel filter, it might be possible to remove it, clean it, or replace it.

When you remove the fuel filter, you might see a little mesh at the bottom of the housing.

If this mesh has clogged, you might be able to clean it away with clean shop rags, and it will allow enough fuel to pass through to the filter and the combustion chamber.

3. Could It Be A Problem With The Air Filter

Two-cycle and four-cycle engines rely on a careful blend of gasoline and air to fire correctly.

The air filter is designed to capture things like dust, pollen, and other airborne debris before they can enter the combustion chamber.

As time goes on these small particles can essentially crust or permeate the air filter preventing sufficient airflow for combustion.

You should take out your air filter and either clean it or replace it every spring.

If it’s been a particularly dusty summer, or the filter is very old, you may simply need to replace or clean it to remedy the problem.

4. A Bad Spark Plug Can Keep A Weed Eater From Starting

Small engines typically have one spark plug. They rely on the tiny electrical burst it produces to ignite the fuel and air mixture in the combustion chamber.

As time goes on, a spark plug can start to build up carbon and other residues, which can prevent it from firing or cause it to misfire.

This is more likely to happen with a two-cycle engine, which tends to leave more residual carbon behind.

Especially if the gas and oil are not always mixed in the exact ratio. Carbon buildup on the spark plug typically reveals itself over time, causing the weed eater to lose power.

It might also take more and more frustrating pulls of the chord to get it to fire up. Most of the time a spark plug won’t just die on your out of the blue.

However, it is possible for the ceramic material to crack. When this happens, the engine can die unexpectedly and refuse to start again.

If a visual check shows that a spark plug is broken or misshapen, you will need to replace it.

5. Carburetor covered in sludge or small bits of lawn debris

The carburetor is the place where air and atomized fuel combine. As time goes on, it’s possible for corrosion or carbon to build up in the carburetor.

It can eventually reach a point where the carburetor simply can’t function properly.

In the case of carbon buildup, and residue you might be able to clean it up with a generous spray of carb cleaner.

If you look down the throat of the carburetor and you see excessive rust or other signs of corrosion, you will likely need to replace it.

How to Fix?

If you are mechanically handy, you might be able to do it on your own. Most small engine carburetors are inexpensive, which will save you a little money.

Whether you want to fix lawn equipment yourself or maybe you’re not a DIY kind of person, a lawn mower repair shop should be able to quickly remedy the problem.

Just keep in mind that they tend to get backlogged in the spring and early summer. So, don’t procrastinate getting on their list

6. A Flooded Engine Causes starting issue on a Weed eater

When an engine fails to fire up after a reasonable number of pulls, it can leave excess gasoline in the combustion chamber. This is often referred to as “flooding the engine.”

The combustion chamber relies on the electric discharge from the spark plug to ignite the fuel-air mixture. The gasoline needs to be atomized, in order to combust.

When it pools inside the combustion chamber it makes it nearly impossible for the engine to fire properly.

How to Unflood a Weed eater?

In a situation like this, you will likely smell the excess gasoline in the air. Sometimes you simply need to wait a few minutes for the excess fuel to evaporate.

You can also set the choke control to “Run” and pull the cord. It likely won’t start, but it should help discharge some of the excess gasoline from the combustion chamber.

Once the strong smell of gasoline dissipates, you should give it another minute or two. Then choke the engine and try to start it again.

7. Problems With The Recoil Starter

The pull cord has a recoil system that uses a pulley mechanism. Like any moving part, this system can break down with repeated use. They also have a knack for jamming up and twisting.

In the case of a jammed or tangled pull cord, you might be able to open the housing with a screwdriver. It might be possible for you to then free the tangle and try again.

In the case of a broken recoil system, which might leave the pull cord fully or partially extended, you will need to replace the entire mechanism.

8. A Failure In The Battery Or Electric Start

Some newer four-cycle engines come with a battery assist or electric starting weed eater.

While they rarely fail out of the blue, it is possible for a battery to degrade to the point where it can’t provide sufficient charge for the electric weed eater to start.

Regular Maintenance Is the Key

These are some of the more common problems that can keep a weed eater from starting.

Ultimately, the best way to ensure that you are taking care of your string trimmer, whether it’s a lightweight weed eater or walk-behind string trimmer, is to properly store it away for the winter. 

First thing in the spring, you should add fresh fuel, clean or replace the air filter, and double-check the spark plug as well as the carburetor.

In the case of a four-cycle engine, you should also give it a fresh oil change with a new oil filter. It probably wouldn’t be a bad idea to give it a new spool of string along the way.

Proper seasonal maintenance really is the best way to keep your weed eater working at its very best.

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