lawn mower starts then dies

Lawn Mower Starts Then Dies [SOLVED]

When mowing season rolls around, as a homeowner, you’re keen to get out there and get that lawn looking its best. So, there’s nothing quite as frustrating as heading outside and firing up the mower, only to find that it cuts out as soon as you’ve got it going. 

After a long winter hidden away in the shed, your mower may not be performing as it did at the end of last summer. There are a number of reasons that might cause this so if your mower starts then dies, check out our problem solving guide. You’ll likely find that one of these things is the culprit and fortunately, most of them are easily solved so you can be back mowing in no time. 

For the purpose of this guide, we will place our focus on the gas powered lawn mower. These tools are incredibly powerful and deliver an impressive cut but with a lot of maintenance involved, it’s not uncommon for things to go wrong when the mower isn’t properly looked after. If your petrol lawn mower starts then dies or backfires, here are some of the most common causes and how to fix them.

1. Dirty Carburetor

One of the main reasons that you might experience problems with your lawn mower starting and instantly cutting out is to do with the carburetor. This is a component within the lawn mower that aids in mixing the gas with oxygen. As a result of this, combustion occurs and the fuel flow is nicely regulated in order to power the engine (find out how long a lawn mower engine lasts). 

However, if the carburetor is clogged or dirty in any way then this can prevent it from performing as it should. This means that, while the engine might initially fire up, once you pull that cord, it cuts right back out again. 

It’s normal for the carburetor to become dirty as a result of things like dirt and debris, contaminated fuel and other things. But when these aren’t removed, the engine is going to struggle to get going. You might notice other signs that your carburetor is due a good clean including black smoke, less fuel efficiency and a ‘rough’ feeling while mowing.

How To Clean Your Dirty Carburetor

Fortunately, getting your carburetor clean and performing as it should again isn’t a difficult task. There are lots of aerosol cleaners that you can buy in stores and online which are designed to remove any debris or residue from inside the bowl through high pressure. These products contain an ingredient that is able to break down carbon, effectively cleaning the carburetor. 

It is also recommended to buy cleaning accessories to go with these aerosols. Things like nylon brushes are particularly useful as you’ll be able to get into all the nooks and crannies. Here’s a quick step by step guide. 

  • Start by taking the carburetor bowl and its screws out of your lawn mower. You can do this by using a plug wrench and once the screws are loose, you’ll easily be able to remove everything you need to. 
  • Next, you’ll clean the carburetor bowl as well as the screws and the hole. 
  • Start by spraying the aerosol cleaner to get rid of as much dirt as possible. You’ll notice that the nozzle might only point in one direction. In this case, you’ll need to employ the use of your nylon brush to get into any tight spots. 
  • Once everything is clean, you can put the bowl and screws back in place using your plug wrench to tighten everything up. Just be careful not to tighten the screws too much as this can ruin the seal.

Watch this video on how to clean a lawn mower carburetor

2. Defective Spark Plug

As its name may suggest, the spark plug creates a spark within the lawn mower. This spark then ignites the fuel and air therefore creating power. While these are small components of your lawn mower, they’re incredibly important and if they’re not in full working order, you’re going to notice that the engine will start but suddenly cuts out again as soon as you throttle it.

Another sign that there are issues with the spark plug is that the mower gets through fuel much more quickly. The reason for this is that more fuel is wasted when it’s not ignited and this might cause the mower to emit white smoke.

You can check to see whether there is a problem with the spark plug by simply removing it and attaching it to the inlet. Once you have done this, crank the engine and look to see if there is a spark emitted from the end of the spark plug. If not, this is a sign that it’s broken and needs to be replaced.

How Do I Fix It?

Sometimes, it might not be that the spark plugs are defective; they may simply need to be cleaned. In this case, you can use a suitable cleaning solution and a wire brush to remove any residue. Do not attempt to use anything high pressure as this will damage the spark plug.

However, in many cases, it’s going to require a replacement but you’ll first need to locate the spark plug. Thankfully this is easy in most walk behind mowers as there’s a black cable at the front of the machine that covers the spark plugs. When removing the plug, you will need to use a socket wrench in the correct size. Your user manual will give you more information on this.

You can then install a new spark plug in its place and the good news is that these parts are incredibly inexpensive costing around $8 and being widely available.

3. Clogged Air Filter

Just like other components of your lawn mower, the air filter can get dirty, clogged or need a good clean. This is again very normal as you use the lawn mower over time but if it isn’t cleaned, then you’re going to notice problems getting the mower going.

The reason for this is that any clogged dirt within the air filter prevents the flow of air required by the fuel. While you might be able to get the mower going in the first place, after a few minutes, it’ll stop again.

It can be tempting to just remove the air filter in the belief that you are removing the problem but that is not the case. Running your lawn mower without an air filter means that debris and dirt can get into other parts of the machine and cause much more severe damage.

Changing The Air Filter Regularly

It is recommended that you change your lawn mower’s air filter regularly. It largely depends on how often you use the mower as to how frequently you’ll need to change the filter but on average, you would expect to have to do this at least once every three months.

However, in between these changes, you will need to keep on top of cleaning the air filter. One of the easiest ways to do this is by using an air compressor. You don’t need a huge air compressor, just a simple can will do the trick. That said, this method might not work if the air filter is incredibly dirty. In this case, you’ll want to remove it and wash it using warm soapy water. Make sure to let it properly air dry before you put it back into your machine.

lawn mower being repaired

4. Choke Is Loose Or Faulty

If you find that your lawn mower starts then dies quickly after, this could be the result of a faulty or loose choke. This part of your lawn mower is designed to warm up the engine when it is cold which helps it to get going.

You’ll hold the choke which then controls a piece of metal designed to limit how much oxygen gets to the carburetor. The result of this is that you get a much richer fuel mix, allowing the engine to warm up quicker. When the engine has gotten warm enough, you let go of the choke and everything will run smoothly.

Unless, of course, the choke is loose or faulty. In which case, that piece of metal won’t function as it should and not enough oxygen will get in meaning that the spark plug cannot ignite.

How Do I Fix It?

As with many other problems that we have discussed in this guide, it is entirely possible to mend a faulty choke at home. Take a look at our easy step by step guide.

  • You can use your carburetor cleaner to clean the choke and remove any debris that may be stuck to it. This might be the extent of the problem and next time you use the mower, it’ll likely start up without an issue.
  • If dirt isn’t the problem, then you can move onto the next step which is that the choke may need to be tightened. There are several screws that keep this component in place and you can tighten these as necessary. 
  • Note that if the choke spring does not move back to its closed position, this will likely need replacing.

5. Too Much Oil In The Mower’s Reservoir

Sometimes, you might be able to get your lawn mower started but then it dies after a couple of minutes. Many people will have followed the previous tips in this guide by this point but find that the problem persists. In this case, it might be that the reservoir contains too much oil. When you start the mower, too much oil is fed into the engine causing it to cut out.

When this happens, you may notice that the engine cuts out but you might also notice white smoke coming from the mower. If you do, then one of the first things you should check is the oil level. Do this by tilting the lawn mower and keeping it safely propped up with something heavy. Leave it in this position for at least 60 minutes.

After this time has elapsed, try running the mower again. If it keeps going for longer before stalling, this tells you that there is too much oil and you will need to drain it.

How To Drain The Oil

Draining the mower’s reservoir of excess oil is the only way to solve this problem. Again, this is something you can easily do at home. 

  • Start by locating the oil drain plug and loosening it with a wrench. 
  • You will need to check the current oil level using a dipstick as this will give you a rough idea of how much to let out. 
  • Find an appropriate container in which to drain the oil and release the excess into this. You’ll know when you’ve released enough by looking at the marker on the mower; when the oil is at the full level, you’re good to go. 
  • Do make sure that you don’t drain the mower too much as having not enough oil can also cause problems. In fact, the issues as a result of this will likely be worse. So, once you’re done, grab your dipstick again and check the level. If it’s now too low, you can always top it up.
  • Test the lawn mower to see if it runs properly and that any previously seen white smoke has disappeared. 

Watch this video on how to drain your mowers oil

6. Bad Fuel In The Lawn Mower

What a lot of people aren’t aware of is that there is such a thing as bad fuel and this can affect how well your mower runs. Moreover, it’s important to remember that fuel does have a best before date and when it has been sitting in your unused mower for a long time, it will begin to evaporate and cause damage from any residue left behind which will clog up the internal components.

As a result of this, fuel is unable to flow as freely through the mower which can mean that it isn’t as easily able to start or dies soon after starting.

How Do I Fix It?

Sometimes, it is possible to simply add some fresh fuel on top of the bad fuel as this will dilute any nasties within it. But you should only do this if the tank is less than halfway full. Any more than this and the new fuel probably won’t dilute it enough.

This means that you will have to siphon out the old fuel and replace it with some fresh gas. But regardless of which method you use, we would suggest using a fuel stabiliser which will stop any clogging from occurring for a much longer period. Typically, when this product is added, you can leave fuel in an inactive mower for as long as two years.

Should You Call a Professional?

In most cases, the methods we have discussed in this guide will be likely to solve any problems with a lawn mower that starts then dies shortly after. However, it is possible for your tool to experience more serious problems that shouldn’t be attempted by someone that doesn’t know what they are doing.

If your lawn mower is covered by a warranty, you’ll likely be able to get it fixed under this but there’s also likely a clause that tells you not to perform certain maintenance or risk voiding your warranty. Here are some of the things that might require the help of a professional:

  • Carburetor replacement
  • More serious problems with the choke that cannot be dealt with as a DIY project
  • Blockages in the gas line or tank.

However, since petrol lawn mowers are designed to be long lasting pieces of equipment, you shouldn’t have too many problems as long as you perform regular maintenance. Make sure to replace things like spark plugs and air filters regularly, keep your mower clean and deal with issues as soon as they arise. 

Summary

There’s nothing quite as annoying as going out into the garden to tidy up the lawn only to find that your mower starts then dies immediately. If you want to get that grass trimmed and looking perfect today then the good news is that it might be a quick fix.

Things like a dirty carburetor, faulty choke or spark plug, too much oil or even bad fuel could all result in this problem. But you can quickly and easily attend to these issues at home. For more serious problems, we would recommend taking your mower to a professional who will be able to safely and reliably diagnose and fix the problem.

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