weed eataer won't star - how to fix

Weed Eater Won’t Start: Why And How To Fix

You’ve come to tidy your garden and get those pesky weeds and long grass trimmed and neat once again. But when you’ve taken your weed wacker out of the garage, you’ve found that it just isn’t starting up.

Nobody wants to spend ages weed eater troubleshooting but there could be a number of things that have gone wrong. To save you the hassle of having to figure it out on your own, we’ve put together this handy guide on why your weed eater won’t start and what you can do to get it back up and running again.

1. Clogged Air Filter In A Weed Eater

Your string trimmer has an air filter inside it which is designed to allow clean air through the system. The presence of any dirt or debris on this air filter can lead to the weed eater not running as you would expect.

For this reason, it is important to regularly change the air filter as part of your string trimmer maintenance. If you don’t then there is a risk of dirt getting into the engine and causing a whole host of problems. At worst, it’ll result in you having to buy a whole new machine .

How To Fix It

Take the air filter out of its housing and wipe any residue or dirt away from the inside of the housing. In most cases, you will not be able to clean the air filter itself so you’ll need to replace it with a new one.

2. Plugged Fuel Filter In A Weed Eater

From the fuel tank of your weed eater, there is a hose and at the other end of this hose, you’ll find the fuel filter. This filter strains the gas before it gets into the fuel system which ensures that no debris or particles get into it.

However, since the very nature of its job is to remove dirt from the system, it will become clogged at some point unless you make a habit of regularly changing the filter. If you don’t, then the fuel will not be able to flow as freely which can cause problems with your weed eater starting.

Plugged Fuel Filter In A Weed Eater

How To Fix It

Make sure to regularly check the state of your fuel filter and, when necessary, change it for a new one.

3. Incorrect Oil Mix In A Weed Eater

This doesn’t apply to all gas string trimmers but only those with a two stroke engine. These engines are designed to run on a mixture of gas and oil. If you attempt to put just fuel into the tank then this can cause the engine to stop. Not to mention the damage it can do and you’ll find yourself having to fork out for a new trimmer

Usually, a two stroke engine will run using an oil and fuel ratio of either

  • 32:1
  • 40:1
  • 50:1

But since each model is different, it is vital that you check the user manual to find out which ratio your machine requires. This information may also be printed on the fuel cap so check there first if you don’t fancy rifling through drawers to find that user manual!

When you are creating a fuel and oil mix, it’s essential that you use unleaded gas that has an octane rating no lower than 89. The ethanol content should not be higher than 10%. There are oils that are specifically designed for two stroke engines so make sure to look out for these.

How To Fix It

If you have put an incorrect oil and fuel mix into your weed eater, stop using it right away to prevent any further damage.

You will need to completely drain the fuel tank and refill it using the correct mix. You may notice that you continue to have issues after this and if this is the case, then you may need to take your machine to a professional for a more thorough assessment.

4. Bad Spark Plug In A Weed Eater

The spark plug is an essential component in any combustion engine and literally creates a spark to ignite the fuel. However, these small parts can often get covered in oil and carbon and when they’re dirty, they won’t function correctly.

Moreover, the electrode can become burned or the porcelain part of the spark plug may crack and both of these things will affect its function. When this happens, it is unable to produce a spark which results in the engine not running.

Bad Spark Plug

How To Fix It

If your spark plug is dirty then it’s pretty easy to clean it. A wire brush is a great tool for this job if you’re looking to get the most out of your spark plug. However, for an even quicker fix, it’s often best to just replace the spark plug as it’s super easy and affordable.

When you do this, make sure to correctly gap the spark plug otherwise you may find that the replacement does not solve your start up problems.

5. Incorrect Engine Oil

Coming back to engine oil once again and one of the main problems that people find when their trimmer won’t start is that they are using the incorrect engine oil. As before, you can find details of the most suitable oil on the fuel cap so be sure to check this before making your gas and oil mix.

Now, if you are using a four stroke engine then you’ll notice that the oil and fuel do not go into the same port. They must be kept separate. Using an oil designed for a two stroke engine is going to cause problems from the off so always avoid this.

However, you do need to use oil in a four cycle engine as this ensures that the internal parts are kept lubricated. But if incorrect oil is used then there will be a build up of friction which can lead to overheating and starting problems.

How To Fix It

If you have used incorrect oil then you will need to drain the tank and refill it using the most appropriate oil with the correct grade. However, do keep in mind that the viscosity of the oil may need to be changed depending on the current temperature especially when the weather is very hot or very cold.

As before, if you continue to have problems after adjusting the type of oil you’re using then it could be that the trimmer needs to be looked at in a shop.

6. Old Fuel

You should never leave old fuel in a string trimmer if you aren’t planning to use the tool for the next 30 days or so. Not only can this cause damage to your engine but it’ll also mess up the carburetor due to the fuel breaking down in the tank.

Fuel contains ethanol which draws in moisture from the air. When this air mixes with the fuel, the result is a sticky, gummy substance that lines the inside of the fuel tank and other parts of the fuel system.

If you cannot use fuel within 30 days then it is best to remove it from the tank where possible. However, you can also add a fuel stabilizer which should increase its lifespan so you can leave the string trimmer in storage for a little longer.

How To Fix It

Make sure that you always use the correct fuel which should be no lower than 89 octane and contain no more than 10% ethanol. Using fuels such as E15 or E85 are only going to cause damage to your engine. Moreover, you may find that using these fuels voids your warranty.

When you are storing the trimmer, be sure to drain any old fuel out of the tank. The next time you come to use it, refill it with fresh fuel and, if you’re using a two cycle trimmer, don’t forget to create the right fuel and oil mix.

7. Bad Primer Bulb

If your string trimmer’s primer bulb is cracked or otherwise damaged then it isn’t going to fill up with gas and this means it won’t work properly. The result is that fuel is unable to reach the carburetor and so the weed wacker won’t fire up.

bad prime bulb of weed eater

How To Fix It

Where there is damage to the primer bulb, the only solution is to replace it with a new one.

8. Blocked Fuel Line

If you’ve made the mistake of leaving old fuel in your string trimmer then the gummy residue it leaves behind can affect the entire fuel system and that includes the fuel lines.

When this happens, fuel is not able to easily flow through which limits how much actually makes it to the engine. The result? A trimmer that won’t start.

How To Fix It

If your fuel line is blocked or damaged then you will need to replace it with a new one. Check regularly for signs of damage such as kinks, cracks, and of course, clogs.

9. Plugged Fuel Tank

In the fuel tank, there is a vent which is designed to let air into the tank. Without this component then there would be a vacuum within the fuel tank and this would prevent fuel from being able to flow through it.

However, when this vent gets blocked, you start to experience the same effect meaning that the string trimmer won’t run as it should. This usually happens shortly after starting the trimmer up; it may fire up initially but a few minutes in and it’ll cut out.

The only way to get it to start again is to release the vacuum by taking off the fuel cap. But once you replace it again, the same problem occurs over and over.

How To Fix It

In this situation, you will need to replace the vent in the fuel tank to allow air to start flowing through again. You’ll need to look at your user manual for instructions on how to do this as models can vary. There are some that have the vent in the fuel cap while others have vents attached to a line that comes out of the fuel tank.

10. Dirty Carburetor

Carburetors are designed to regulate how much fuel is mixed with air and in turn, this allows combustion to occur. These parts can often become clogged with old fuel which affects its function.

clean or adjust carburetor

How To Fix It

Most people find that cleaning the carburetor is a pretty straightforward job. You can buy a special carburetor cleaner but you will need to take the carb apart in order to use this.

If, after you have cleaned the part, you find that you’re still having starting problems, it could be that you need to replace the carburetor entirely. If you’re unsure on how to do this, it’s best to have your trimmer looked at by a professional.

11. Bad Recoil Start In A Weed Eater

Gas weed wackers use a recoil start which gets the engine going. If there are any broken parts such as springs, a dodgy pulley or even a broken clip, this can stop the recoil from functioning and you won’t be able to start your trimmer.

How To Fix It

It is possible to replace certain parts of the recoil start including the string and the spring. However, this may not always be successful and you may need to admit defeat and just replace the whole lot.

12. Flooded Weed Eater

Sometimes, when your weed eater won’t start, it’s because the engine has flooded. This sounds like a terrible problem but it’s not as bad as you might imagine.

This usually happens if the choke is left closed when the recoil was pulled several times. This causes a lot of gas to go into the carburetor. However, it can also become a problem when you push the primer bulb too many times.

How To Fix It

The good news is that it’s simple enough to unflood a string trimmer engine and you’ll need to start by turning the switch to the run position and putting the choke in to run.

Next, while you pull the recoil several times, press the throttle trigger. Note that this may take up to fifteen pulls before you get your trimmer running again and it’ll likely sputter before it starts running smoothly.

Final Thoughts

A string trimmer that won’t start is really frustrating but there’s usually a relatively easy solution to the problem. Since these weed eaters run on complex combustion engines with several parts, there is scope for things to go wrong. But with a little weed eater troubleshooting and some quick DIY, you’ll have your machine working again in no time.

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Andrew Fisher

Andrew Fisher

Andrew is a dedicated father of three who really takes pride in his lawn and garden. You'll find Andrew behind the scenes of almost everything Edge Your Lawn produces. When he's not helping readers find all the information they need, he's in his backyard working on his lawn and garden landscaping. This year he hopes to build an outdoor deck and sort out his veg patches.

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