Riding lawn mower backfires. Why Does a Lawn Mower Backfire? (and how to prevent it)

Why Does a Lawn Mower Backfire? (and how to prevent it)

As an Amazon Associate we earn from qualifying purchases made on our website. If you make a purchase through links from this website, we may get a small share of the sale from Amazon and other similar affiliate programs.

Is your lawn mower’s engine popping, hesitating or backfiring? Maybe the engine just doesn’t sound right. At this point you may be wondering why lawn mowers backfire. You’ll also be interested to know if this is this causing any damage to your engine and what you need to do about it.

One of the most nerve-racking sounds you can hear when starting a lawn mower is a backfire which tends to be a common problem after winter storage. Most commonly, lawn mowers backfire because of a failing spark plug or a dirty air filter resulting in incomplete combustion.

Let’s look into what that means and what you should do about it.

What Happens When a Lawn Mower Backfires?

When you try to start your lawn mower and it backfires, there may be ab engine timing issue but most likely it’s a result of incomplete combustion of the fuel. In other words, the fuel is not being burned properly which can cause stuttering, unusual sounds and even black smoke being blown out of the mower.

You may find that your mower will not start at all, lose power or run rough.

This can certainly be a cause for concern, so let’s dive a little deeper into why you may be experiencing some of these problems.

Why Does a Lawn Mower Backfire?

Engines often backfire when there is an improper air to fuel mix. It can be difficult to know what exact component of your lawn mower is causing the problem but we’ve found some of the most common causes and put them together below.

Of course, with most mechanical issues, a certain level of troubleshooting is required to get to the root cause of the problem.

We’d recommend starting by checking the fuel supply, the air filter and the spark plug first. Removing the carburetor and checking for a malfunction there is probably the last thing you should check since it can be tricky to remove and put back on.

Air Filter

Sometimes after running your mower for some time, the air filter can become blocked with all kinds of debris like crud, grass clippings or paint chips. The air filter in a lawn mower acts to prevent these particles from entering the engine as a first line of defence. Once it becomes clogged, you may experience strange engine sounds, a misfiring engine, reduced fuel efficiency or even black smoke from the exhaust.

Spark Plug

Over time your spark plug will accumulate wear and tear. A failing spark plug is one that is unable to produce enough current to spark the fuel. A light gray color is usually a good indication that it’s operating properly. Sometimes it can become chipped or black and carbonated over time. A worn or damaged spark plug can the engine to stall or have poor fuel economy.

Fuel Filter

The fuel filter screens out dirt and debris from entering the fuel. Old fuel can clog up the fuel filter which may prevent it from effectively filtering out any impurities. If you’re unable to see any light through the filter, this may be an indication that it’s gone bad.

Fuel

The fuel you’re using in the mower may be old or have a higher amount alcohol than necessary.

Incorrect fuel maybe preventing the proper function of your engine by clogging up essential components.

You might also want to check that there is no water contaminating your fuel. A good way to do this is to take off the float bowl to take a look inside. You may see tiny droplets of water in the bottom and if this is the case, you need to drain the fuel out and replace it.

Carburetor

Your carburetor is responsible for creating the right fuel to air mixture in order for complete combustion to take place.

Sometimes, the residue from old fuel can create problems in the carburetor. The holes may become clogged with debris resulting in malfunction and of course, could result in incomplete combustion so they will need to be addressed.

Does a Backfire Damage the Mower’s Engine?

Overtime it could cause extensive wear to the engine and other essential components of your lawn mower.

A backfiring lawn mower will result in suboptimal lawn mowing and wasted fuel so there’s plenty of reason to get it fixed straight away.

How to Stop a Lawn Mower From Backfiring?

Proper maintenance and regular service of your lawn mower can go a long way to help your mower’s engine to run smoothly.

Below are some steps that you can take to in order to prevent your mower’s engine from backfiring.

Before you replace anything on your mower, it’s best to consult the owner’s manual for the best practice although we do appreciate this may be long gone for some of you out there!

Unclog the Air Filter

You can start by making sure the air filter is unclogged. Dust, grass and other debris can block it up. A dirty air filter can stop good air flow from reaching the engine so you’ll want try and remove the air filter and use some compressed air to clean it up.

You may even want to replace the air filter if it’s really dirty. They are cheap and it’s not difficult to do.

Clean the Spark Plug

This probably needs to be replaced about once a year or so but you may just need to clean it rather than put a new one in. You can also use an ignition tester to see if it’s faulty. Double check the lead while you’re at it too. A damaged lead could cause the circuit to be incomplete.

If the plug is fouled with oil and sand, the best tool to clean it with is a pneumatic spark plug cleaner. You can connect this to an air compressor and it can be used over and over. On the other hand, spark plugs aren’t that expensive. If only have one mower it may be worth just replacing it.

Use the Correct Fuel for Your Mower

Always use fresh fuel when filling the fuel tank along with a stabilizer to make sure the fuel quality remains optimal. Always remember to following the manufacturers recommendations on what fuel you should be using. If you have too much water in the fuel, you will need to drain it out and start over. This can be caused by leaving your lawn outside which can cause you to accumulate water in your float bowl.

Once you’ve checked the air filter, spark plug and added a little fuel to make sure there’s plenty to get down into the carburetor, it’s likely a fuel flow issue. You can start by spraying some starting fluid into the throat of the carburetor to see if it will run in short bursts. If it will run, it’s probably something to do with the carburetor which you’ll need to take out.

Clean the Carburetor

When you remove the carburetor, be sure to take note of how the mechanisms attach together so you can put it back in the right order.

You can also try cleaning the carburetor with carburetor cleaner to eliminate any clogs. Use a paperclip or a guitar string to help clean out the holes, and combine this with an air compressor for the best results.

This should be enough to get the job done, but if it wasn’t effective, you may need to purchase a carburetor repair kit in order to either replace any faulty components or put in a brand new carburetor.

Replace the Fuel Filter

A degraded spark plug will need to be replaced to prevent the engine from stalling. You will need to check it for any damage and replace if necessary.

Winterize Your Lawn Mower

If you’re planning to put your lawn mower away for the winter, you’ll want to winterize it before doing so. This is a great yearly practice that you should do to keep your mower in the best condition possible. If you’re unsure on how to do this, we have an extensive guide here to walk you through what you need to do.

In Summary

The above steps should cover any issues that might be causing your lawn mower to backfire. If the problem persists, you may need to get someone to look at it. Nevertheless, troubleshooting on your lawn mower can save you a lot of money and can actually be quite rewarding too!

Why Does My Lawn Mower Backfire? How to Fix it

If you buy something through our posts, we may get a small commission. Read more here.

Encountering problems with your lawn mower is frustrating. Hearing that loud bang will catch you off-guard, and now you’re wondering why it suddenly backfires.

Given how surprising the noise can be, you might be frightened or alarmed for your safety. Here we put up a guide to relieve you and help you understand why does your lawn mower backfire.

What Causes Backfiring in My Lawn Mower?

There are a lovely couple of reasons why your mower backfires, and knowing what they are is essential to getting the right fix. While it may not directly impact your engine, it can damage the exhaust system if left untreated.

Common reasons include bad gasoline, damaged spark plugs, and mishandled carburetor. There are also cases where backfires occur when you shut it down or it’s shut off.

Here, we’ll detail the probable reason for these occurrences and the right fix to get your lawn mower back running.

When Does it Backfire?

One telltale sign that your lawn mower is backfiring is when you hear a loud bang from the gas ignited outside the normal combustion chamber. A backfiring engine happens at different moments, either when you’re trying to start it while it’s running or as soon as you turn it off.

Keep tabs on the moment when a backfire occurs, as this is essential in assessing what the issue is and how you can fix it.

Lawnmowers are called small internal combustion engines, and they operate at high temperatures, which is another reason it tips over easily. Elevated temperatures can also prompt problems with the air intake, so it’s best always to clean the air filter and ensure increased airflow.

Issue #1: Lawn Mower Backfires and Won’t Start

If your mower starts then dies or you see splutter and backfires, the problem is with the engine’s timing. It can backfire through the card, so it’s best to check the flywheel. One common reason for lawnmower engine backfires are damaged flywheels.

Through time, it’s inevitable for the parts to tear and wear. However, flywheel breaks happen if you accidentally hit a hard object or rock when you’re using the mower, causing shears on your flywheel.

To check so, partially disassemble the mower, and assess for sheared keys. The key should match the keyway hole on the crankshaft, but the engine timing will be faulty and altered with sheared keys. This results in synced spark plugs and engine valves.

Solution

The best solution for a broken flywheel is to replace it. Check the rest of the flywheel, assess for small cracks or damages, and inspect the crankshaft conditions. These are vital parts of the machine, and getting these two checked and replaced will solve the backfiring problems.

Issue #2: Lawn Mower Backfires While in Use or Running

What caused your lawnmower to backfire suddenly in the middle of operations? Check your carburetor. When a carburetor gets too lean or too rich, this can lead to incorrect carburetor settings.

The carburetor is made to equally distribute air and pump an equal fuel mix for the proper combustion, but if there’s more air or more fuel, it will result in the lawnmower’s backfire.

Solution

To fix this, identify the location of your lawn mower’s carburetor. Then, adjust it until it holds the right amount of gas into the engine. This may also need professional help, so we highly recommend hiring a qualified technician.

They know the right air mixture and can assess what other possible fixes can be done to the carb.

Issue #3: Lawn Mower Backfiring While Turning it Off

Another common occurrence of backfiring happens just when you’re about to turn it off. When this happens, it can be frightening since the sudden noise is overwhelming.

Our experts did a few experiments on this and found that the common reason for lawnmower backfire incident is when you’re forcing your mower to run at full speed and then suddenly bringing it to a halt.

Like when you’re running, as soon as you drop your speed, you’ll hear loud heartbeats. This is basically what happens when you do that on your machine. The fuel continues to pump even when you’ve gone full halt already.

Backfiring can also occur when the muffler gets very hot, then suddenly sparks with unburned fuel vapor, causing the bang sound.

The engine speed builds up during operation, and when you slow it down too quickly, it could pump gas to the mower’s muffler. The engine is overheating, and the gas could ignite and cause a backfire.

When you shut off the engine right away, it causes fuel to pump continuously and ignite the engine—overheating the engine results in your mower backfiring, which stems from the lack of airflow into the engine.

Solution

Avoid engine backfire by gradually decreasing the engine speed before turning off your machine. Slowing the speed gradually ensures the excess fuel doesn’t snip through the exhaust system, increasing airflow.

While many mowers have shut-off valves, it’s not recommended to use this when shutting off an engine running at full throttle, causing fuel to pump and ignite the engine.

Issue #4: Lawn Mower Backfiring When it’s Turned Off

Does backfiring still happen even when the lawn mower has turned off already? Unfortunately, in this case, yes. In some instances, lawnmower backfire can still occur even after shutting off, and the culprit is either the muffler or the carburetor.

If any of these two are incorrectly adjusted, or the muffler is on faulty construction, engine backfiring will occur.

Another possible reason why a lawnmower backfire occurs after shutting off is you’re using the wrong type of gasoline. Backfire occurs when you use fuel with high alcohol components, as alcohol ignites differently.

Solution

To fix this dilemma, adjust the carburetor and muffler accordingly. Make sure these two components are prioritized. However, if you believe the problem is with gasoline, switch to gas with lower alcohol content. An alcohol-less gas would be better.

Why Does my Lawnmower Backfire? – SOLVED

If your lawnmower has ever backfired, you will be familiar with how loud and quite frankly, scary this can be. But this is, unfortunately, something that happens with a lot of garden tools over time. When you first purchase your lawnmower, it will likely give you a smooth operation and very few problems.

The issue with this is that a backfire can cause damage to the engine, which could be costly for you in the long run. But it’s still a head-scratcher; why does my lawnmower backfire? In this article, we are going to look at this in a little more detail and put an end to your backfiring problems!

Backfiring and How Small Engines Work

When you notice that your lawnmower engine is making a popping sound or something even louder that might resemble an explosion, it can be worrying. It is true that a lawnmower backfire is a small kind of explosion, but it is unlikely to ever cause any harm to you. But your engine may not be as lucky. The same goes for when your lawn mower starts and then suddenly dies.

The motor found in your mower is considered to be a small internal combustion engine. Inside the engine, there is a combustion chamber and this is where the magic happens and power is created. Here, air and fuel combust and this process can happen in either two or four cycles; this is where we get the terms ‘2-cycle’ and ‘4-cycle’ engines.

During this process, a spark is initiated as the fuel and air mix and this will always set off a mini-explosion of sorts. However, this happens inside the combustion chamber so is both controlled and won’t affect any parts of the engine negatively. However, if this process takes place anywhere else apart from inside the chamber, then we hear the ‘explosion’ and this is what is known as a small engine backfire.

Riding and Push Mowers

Both riding and push mowers that run on a gas engine may backfire at any time. But since a riding mower is typically a lot more powerful you may find that the backfire is louder but this depends on the size of the engine and the chemical reaction.

Quite simply, if fuel comes into contact with a spark outside of the combustion chamber, you are going to get a little explosion. So whether you are asking why you riding lawn mower is backfiring while running or why you keep experiencing a push mower backfiring, the common causes are likely to be similar.

Common Issues

There are people all around the world scratching their heads and wondering why does my lawnmower backfire? If you are one of them, the good news is that while there are several common causes of what causes a lawnmower to backfire, for the most part, they are easily remedied. Let’s take a look at what the issue may be and how you can solve it.

Fuel-Related Issues

One of the most frequently reported issues when it comes to a push mower backfiring is a problem with the fuel. When the fuel is inside the combustion chamber, it must have oxygen in order to burn and your lawnmower’s engine will have been specially designed so that it has just the right fuel to oxygen ratio for an efficient burn.

However, if for some reason, this ratio is interrupted, then problems are bound to follow. A good example of this is using the wrong type of could cause the engine to smoke. Another example of this is if the timing inside the chamber is off, this could result in the fuel to oxygen ratio being interrupted and, therefore the lawnmower may backfire.

Typically, this would happen if too much oxygen is present and in this case, no spark would be produced. But this doesn’t mean that the rest of the process will stop meaning that there may be a resulting build-up of fuel which has a chance of igniting once it is outside the combustion chamber.

How to Fix Fuel-Related Issues

Firstly, make sure you’re using the right type of fuel for your mower’s engine. You would most commonly notice this problem if the components of the engine are outdated and not functioning as they should. Components such as the fuel pumps and filters may simply need updating and this can often solve the problem.

Engine Related Issues

If there are no problems with the fuel, then it could be an issue with the engine. This can be concerning as many lawn mower owners may think that a faulty engine means the end of their mower’s life. In some cases, this may be true but where backfiring is concerned, it is likely a fixable problem.

Similarly to when there are problems with fuel, engine problems are often a result of timing with the processes. If you want your engine to run smoothly and without issue then everything needs to run like clockwork. If it doesn’t, then you may find that your lawnmower starts backfiring unexpectedly.

In much the same way that fuel could pool in the motor and ignite outside of it, the timing of the engine could cause fuel to spark in the wrong place. But in this case, it is less of a problem of where but when in the process. If the fuel sparks while the intake valves remain open, then a backfire will be the result. This is common in older engines but as we have mentioned, doesn’t have to mean replacing the entire lawnmower.

How to Fix Engine Related Issues

Where a fuel-related issue can be easily fixed, a problem relating to the engine may require a little more hard work. However, you will normally find success by addressing one of the following issues.

Tune-Up the Engine

Replace or Clean the Fuel Filter

As well as looking at how long the battery will run, it is also a good idea to look at how long it will take to recharge. If you want to give it a quick boost, there are plenty of products out there with fast charging times. this is convenient and adds to the easy use of these tools. In order for your machine to remain happy and healthy, there needs to be a degree of cleanliness. In this respect, we are referring to the fuel filters; if they are not kept clean, they cannot filter effectively and this may cause backfiring. If your lawnmower backfires regularly, then it could be a simple case of replacing the fuel filters.

Clean The Spark Plug

If the problem does not appear to be the tuning of the engine or an unclean or old filter, then it is likely that the spark plug needs a clean. A clean spark plug will help to make sure that the ignition happens at just the right time. If it looks as though it needs a clean, be sure to pay attention to the chamber of the spark plug as well as the wires.

Lawnmower Backfires During Starting

If your lawnmower backfires when trying to start then this is, unfortunately, never a good sign. It could signal that the mower is in need of repair since unlike other problems, when a lawn mower struggles to start without backfiring, this is not normal and may need a professional to take care of the problem.

A petrol-powered lawnmower is an expensive bit of kit and this is because there are a lot of intricate parts that cost a lot to manufacture and can cost an arm and a leg when it comes to replacing them. For this reason, many gas lawn mowers have other, less expensive parts that are designed to break first. You might see this as some sort of barrier to the pricey parts or even some kind of weird, garden tool self-sacrifice. But in any case, a mower that backfires upon starting isn’t a good sign.

One of the first parts to go would be the flywheel. This will normally be the result of some sort of direct damage to the mower, such as mowing over a large stone or hard piece of debris, but rather this than the crankshaft breaking as that would be a much more expensive repair. Once the flywheel is broken, it will not work and this can cause the lawn mower engine popping sound or backfiring that is causing you so much concern. In some cases, the mower will refuse to start at all so the only solution is to have it repaired.

Lawnmower Backfires During Shut Off

A lot of gas mower owners will quickly shut down their gas mowers when they have finished mowing. During this short shut down period, backfires can be pretty common. If you notice that your lawn mower pops when turning off then there is usually a very simple cause for this which can be quickly and easily solved.

Typically, this problem occurs because the mower engine is being slowed down too quickly. As you use your lawn mower the engine speed will increase over the course of the mow. However, just as it needs time to build speed, it also needs time to slow down. If it doesn’t have this time then the muffler could become filled with gas where it will spark and result in a backfire.

In order to avoid backfiring like this, it is important not to turn the mower off as soon as you finish mowing. Give it the time that it needs to slow down by leaving it running in idle for ten minutes.

However, this may not be the only reason that your lawnmower backfires when shutting down. There may be an issue with overheating which is typically related to a lack of decent airflow around the engine. This is a problem that needs to be addressed by a professional repairs-person.

Lawnmower Backfires After Shut Off

If you have managed to start your mower, complete the cut and then get it to shut down without it backfiring, it can then be pretty disheartening when it backfires the second it shuts down. If this happens, you’ll likely find that there is an issue with either the muffler or carburettor. In this instance, you will need to have the lawnmower checked and repaired.

However, you might also experience problems if you are not using the correct type of fuel. Normally, using a non-alcohol fuel will reduce the number of backfires, almost completely eliminating them.

Anti-Backfire Equipment

If you continue having problems with your lawn mower backfiring at shut off then there are special pieces of equipment known as anti after fire solenoids which can be used to prevent the problem in future. However, this is not something that the average homeowner can fit on their own and it is important that you take your lawnmower to a professional to have these fitted.

Once installed, this feature will mean that you no longer have to idle the mower after use and before shutting off. This can make the mowing experience a lot more convenient.

Conclusion

Gas-powered lawn mowers are very effective and powerful tools that can make light work of mowing your grass, especially if you have a larger garden. However, they are not without their problems and one of the most common is that a lawn mower will backfire at any point during operation. If you’re still running into issues with your mower, consider buying a secondhand mower or cheaper model that won’t break the bank.

There are several causes for this but for the most part, they are easily fixed either at home or by taking the mower to a professional repairs person.