Why lawn mower backfires. Lawn Mower Engine Makes Popping Sound: Reasons and Fixing Tip

Why Is My Lawnmower Shooting Flames? Expert’s Interview

Lawnmowers are sensitive machines, and every part plays an important role in running the engine smoothly. If anything happens to any of the components, it may prevent you run the machine smoothly.

Why is my lawnmower shooting flames?

One of the main reasons could be that the exhaust system is filled with unburnt fuel, ultimately causing firing issues. Since it is a serious issue, you want to address it soonest to prevent damaging the exhaust manifold and other components.

  • Why Is My Lawnmower Shooting Flames?
  • Giving Pressure
  • Cutting Tall And Thick Grasses
  • Fuel Hazards
  • Excessive Fuel
  • Poor Performance Of Spark Plugs
  • Using Old Fuel
  • Imperfect Air/Fuel Mixture
  • Bent Valve Or Valves
  • Wrong Ignition Timing
  • Older Lawnmower
  • High Engine Temperature
  • Adequate Oxygen
  • Air leakage
  • Replace Spark Plugs
  • Maintaining A Healthy Exhaust

Why Is My Lawnmower Shooting Flames?

There could be several reasons your lawnmower is shooting flames. Since it could lead to dangerous accidents, you want to address it soonest. Here are all possible reasons when you want to know about “Why is my lawnmower shooting flames?”

Giving Pressure

Are you giving more pressure to the lawnmower? When you mow grass for several hours without any single break, the engine becomes excessively hot.

As a result, the piston moves slowly, and it fails to comply with the firing cycle of the spark plug. Some portion of fuel fails to burn and moves to the exhaust system without burning.

Finally, when the ignition system starts, your lawnmower is likely to shoot flames. The earlier you stop the machine, the better it is.

Cutting Tall And Thick Grasses

Do you cut tall and thick grasses often? Have you checked whether the mower deck doesn’t stick anything?

If the blazing hot muffler is completely filled with grasses, your lawnmower has a probability of shooting flames. At worst, this may burn out the lawn too.

Fuel Hazards

The normal stability of a lawnmower motor is compromised if fuel leaks in the engine. This can lead to flame. In addition, if a hot muffler is surrounded by fuel vapors, it can also cause a flame.

Excessive Fuel

Initially, if excessive fuel exits inside the combustion chamber, your mower may shoot flames. So, why it occurs? It occurs when the air-fuel mixture becomes excessively rich from the adjustability of the carburetor.

Poor Performance Of Spark Plugs

Are the spark plugs performing the way they should be? If there is a lack of oxygen, incomplete combustion occurs, making the spark plug weak or misfiring.

At first, this will lead to smoking. Then extra heat is generated, making the exhaust hotter. At last, flames will come out from the exhaust pipe.

Using Old Fuel

Are you using too old fuel for your mower? Changing fuel is necessary once a month. Old fuel may lose its quality when it sits idle for a long time. Using this old fuel can cause smoking issues and ultimately shoot flames.

So, these are the possible causes you want to check out if you wonder, “Why is my lawnmower shooting flames?”

What Does It Mean When Your Lawnmower Backfires?

Is your lawnmower backfiring? Not taking immediate action will lead to heavy damage to your mower.

What does it mean when your lawnmower backfires?

When your lawnmower engine backfires, it is failing to generate the same amount of power it used to do. As a result, fuel inefficiency occurs, and the machine uses more fuel to produce energy. You may also hear loud popping noise coming out from the mower.

So, what are the signs of misfiring a lawnmower? You can understand whether your lawnmower is misfiring or not by checking out these symptoms:

  • The unpleasing smell coming from the mower
  • The mower makes unusual sounds when it runs on
  • The engine is losing its power
  • You may struggle to start it
  • the exhaust pipe is releasing an excessive amount of smoke

You have already learned about “What does it mean when your lawnmower backfires?” and “What are the symptoms of misfiring lawnmower?”

Here are the possible reasons you should check to learn to find the reason behind misfiring issues in your lawnmower.

Imperfect Air/Fuel Mixture

You should neither have a high or low air/fuel mixture. The ratio should be stable — not too low or too rich.

If there is a low air/fuel mixture, the engine has less fuel but high air. Imbalanced ratio. This may happen due to low fuel pressure. It is also known as “lean mixture.”

When it happens, some fuel and air fail to reach inside the exhaust valves at the right time as they burn slowly. As a result, backfiring occurs.

Bent Valve Or Valves

A lawnmower has several cylinders, and each cylinder includes one exhaust valve and one intake valve. The job of an exhaust valve is to pass burned gases from the cylinder.

On the contrary, the intake valve enables an ideal air-fuel combination to enter the cylinder.

However, when a valve vent, it doesn’t have a perfect close or opening. As a result, the fuel fails to pass through the exhaust or intake valve to combust. This leads to backfiring issues.

Wrong Ignition Timing

This is the best ignition coil for a lawnmower available in the market.

When wrong ignition timing occurs, the spark will fire either too late or too late. In both cases, the intake or exhaust valve may combust, causing backfiring. You can’t diagnose this problem unless you are a professional mechanic.

Older Lawnmower

Are you using an older lawnmower? Latest lawnmowers are tuned up finely through computer systems. That’s why they can constantly adjust their internal system to make the mower run smoothly.

However, the older lawnmower may not do this like the latest models. They often fail to control the sparks when it is fired and the perfect air-fuel ratio.

High Engine Temperature

Commonly, your lawnmower temperature will rise when you use it. But if the temperature increases unusually, there is something concerned.

When this happens, you may notice the engine is backfiring and automatically shut down after running for several minutes.

Can A Backfire Damage An Engine?

The backfiring issue occurs for several reasons, which we have already discussed above. It will prevent you from running the machine normally.

Can a backfire damage an engine?

A backfire can damage the engine heavily if neglecting the issue for a prolonged time. You want to address the problem as early as possible to prevent damaging it completely.

How to stop backfiring issues for your lawnmower? Here are a few points you want to apply if your lawnmower is backfiring and save from extra damage.

Adequate Oxygen

Does your lawnmower have the perfect amount of oxygen? An ideal amount of air fuel is required to run the mower smoothly. It should be neither too rich nor too low.

When the oxygen level drops, excessive fuel will enter the system. Also, a high level of oxygen (air) will prevent entering an adequate amount of fuel.

Air leakage

Is Your Mower Has Air Leakage? If there is any leakage issue, you want to solve it soonest.

Replace Spark Plugs

Replacing spark plugs after a certain time is necessary. Over time, its construction weakens due to long-time use.

lawn, mower, backfires, engine

Using new spark plugs ensure perfect spark firing at the right time, also preventing backfiring issues.

Maintaining A Healthy Exhaust

The exhaust system is one of the most common parts where backfire occurs. This mainly happens when the exhaust system is unhealthy.

Proper functioning will be carried out because of this. That’s why maintaining a healthy exhaust system for your lawnmower is necessary.

Hopefully, you have learned about “Can a backfire damage an engine?” and how to stop this issue.

Can A Lawn Mower Explode?

Explosion for any engine can damage it and even make the owner heavily injured.

Can a lawnmower explode?

Yes! A Lawnmower can explode if it is a gas-powered rotary mower. If a leakage issue is seen in the gas tank, it may fire and create a small explosion.

While filling the gas tank, you want to make sure no spelling issues. Being uncareful, you may splash it on the hot muffler, causing firing issues and explosion.

Replace your muffler with the Best muffler for lawnmowers.

The tall grass is one of the primary reasons that could lead to a fire in the lawnmower. That’s why it is better to mow your lawn regularly, ensuring good conditions for your lawn and mower.

So, why do tall grasses cause firing and explosion issues?

The taller the grasses, the bigger the grass clippings. As a result, bigger grass clippings will stick inside the deck and enter the hot motor, muffler, or exposed parts.

When the clippings contact with the hot parts, they start to burn. After a certain time, they will catch fire and may result in an explosion.

Weather condition is another important thing you should note down. You need to choose a perfect time to mow your lawn, especially in the summer season.

During the season, the temperature becomes excessively hot, especially in the afternoon hours. That’s why you want to either mow the lawn in the early morning or evening hours to prevent excessive heat.


Everyone wants to run their machine without any issues. Sometimes unwanted problems pop up from the engine. Resolving it soonest is what we are supposed to do. Hopefully, you have learned everything about “Why is my lawnmower shooting flames?” and how to deal with the problem.

Last update on 2023-01-28 / Affiliate links / Images from Amazon Product Advertising API

Lee Safin was born near Sacramento, California on a prune growing farm. His parents were immigrants from Russia who had fled the Bolshevik Revolution. They were determined to give their children a better life than they had known. Education was the key for Lee and his siblings, so they could make their own way in the world. Lee attended five universities, where he studied plant sciences and soil technologies. He also has many years of experience in the U.S. Department of Agriculture as a commercial fertilizer formulator.

Thoughts on Why Is My Lawnmower Shooting Flames? Expert’s Interview

Lawn Mower Engine Makes Popping Sound: Reasons and Fixing Tip

Did you hear the Lawn Mower Engine Popping Sound? Well, this could seem dangerous. Relax because the backfiring or popping sound made by your mower engine is not serious but it does point to other issues that need to be addressed immediately.

So what exactly is this popping sound and why is it caused? Also, what can be done to fix it? Get all the information in this article.

What is Popping Sound on Lawn Mower?

A popping noise or a backfire is caused when the gasoline ignites outside the engine’s combustion chamber. Your mower may be working properly with no trouble and then you unexpectedly hear the backfiring. This explosion can distress you but there is nothing to worry about. However, if left unattended, then the cause behind this backfire could get hazardous for your mower engine.

You must delve deep to figure out what caused the engine to backfire. Once you understand the cause, fix it so that your mower can work normally again.

The popping sound usually occurs when you turn the engine on or off. Having some basic information about the popping sound and ways to deal with it does help.

Why did My Lawnmower Engine Make a Popping Sound?

The mower engine is a small combustion engine placed internally. Power gets produced in this combustion engine through the air-fuel mix combustion. This power production can take place in the 2-stroke and the 4-stroke engine. In both cases, it is the air-fuel mixture combustion that creates a spark to ignite the moisture which causes an explosion and releases energy.

The fuel combustion takes place in the combustion chamber in a controlled environment. If the fuel burns elsewhere then this causes a popping sound.

The popping or the backfire sound is heard when the fuel comes in close contact with the spark outside of the engine combustion chamber. The sound could be caused because of a problem with the fuel or the engine.

Fuel Related Issue and Fix

There is fuel in the engine combustion chamber that needs air or oxygen to burn. Every engine is designed to get the right mixture of air and fuel in the combustion. All the strokes need to be perfectly timed for complete fuel combustion, smooth operation of the machine, and maximum release of energy. If there is an incorrect proportion of the air-fuel mixture then this causes many problems like the engine burning up smoke.

The timing of all the processes in the combustion chamber is important. If a process happens early or late then this causes problems. If there is an incorrect proportion of air-fuel mixture then this disrupts timing.

If there is a lot of air in the combustion chamber the engine does not create a spark because there is enough power to ignite the fuel for some time. The ignition is delayed but the other processes occur in their regular way. This makes the fuel pool in the low spots with the exhaust. The fuel gets ignited outside of the combustion chamber that produces an explosion or a popping sound.

At times the fuel escapes the engine’s cylinder before the valve closes. This could also occur during the exhaust stroke and then the fuel enters the exhaust or the engine. If there is a good amount of unspent fuel that enters the engine and comes in close contact with the spark then this makes it ignite and causes the engine to make a small popping sound.

In a nutshell, if the fuel combustion occurs anywhere apart from the combustion chamber in the engine or the exhaust then this will cause the popping sound.

How to fix it?

If the air-fuel mixture has more amount of air then this is called the low-pressure fuel. If the mower engine is backfiring then this could be because the low-pressure fuel is getting pumped into the combustion chamber of the engine. An old fuel pump or fuel filter could be causing low-pressure fuel.

All that you need to do to rectify the problem is to replace the old fuel filter and repair the fuel pump. If the problem was caused because of the low-pressure fuel then this will fix the issue.

Engine Related Issues

The timing of the engine processes is crucial so that the mower functions smoothly. If there are some issues with the engine that mess with the correct timing then this will cause a popping sound.

Check the timing of the motor to see if the engine is backfiring. If there is an issue with the timing of the motor then this will cause the engine to ignite the fuel even though the internal valves are open.

After using the engine for a long there could arise a problem with the timing of the valve and the engine that could get disrupted. This could also occur because of a simple and basic chemical malfunction.

The problem should be fixed without delay so that the exhaust and engine do not get damaged further to become unrepairable.

How to fix it?

  • An engine tune-up restores the valves and the engine to its correct time setting. This will let both the valves open and close at the right time that and not let the fuel burn in the engine.
  • Spark plug cleaning or replacement helps. Just clean the plug chamber or the plug wire which will ensure the right timing of ignition thus preventing the backfiring sound.
  • Keep the fuel filter clean and replace it each year. Take guidance from your owner’s manual to understand which fuel is best for your mower.

Significance of Timing on Lawn Mower Popping Sound

Now that we have dealt with the issues that could cause an engine to backfire let us understand what significance does the popping sound timing hold.

During the start

If the lawnmower makes a popping sound when you start it then this indicates a damaged mower. Many mower parts safeguard the expensive parts. Like the flywheel will take damage to protect the expensive crankshaft. If your mower runs on a large rock then this can cause the flywheel to break and fail to engage causing the engine to make a popping sound when you start the mower.

A mower that has its flywheel broken will not start automatically. If the mower backfires then this indicates damage and you should take it for professional repair.

During the shut-off

Sometimes you may hear the pop sound when you turn off the engine or when your mower is just lying idle. This happens when you slow down the engine fast. The speed of the engine builds up when it is in operation and when it is slowed down quickly then it pushes the gas in the muffler. This gas gets ignited and causes the popping sound.

lawn, mower, backfires, engine

To reduce the chances of such popping sounds you should reduce the mower speed gradually and let the motor stand idle for around 15 minutes before you turn the engine off.

Engine overheating is another reason why your mower is backfiring when you shut it off. Increasing the flow of air to the engine can reduce it from overheating. If you hear the popping sound during the shut-off and you feel that it could be because of an overheated engine then get in touch with a professional who will increase airflow to your engine.

After shutting the engine off

If your mower makes a popping sound after you have shut off the engine then this could be a problem with the muffler or the carburetor.

To fix it check the carburetor for any incorrect settings. Check the muffler if it is constructed wrongly. Rectifying these issues could solve the problem.

Also if you use the incorrect gasoline then this can cause the mower to backfire after it is shut off. Gasoline with alcohol will ignite differently than the one that does not contain alcohol. When the gas that contains alcohol gets ignited in the muffler then these causes backfire. In this case, switch to gas that contains low alcohol content or uses gas that does not contain alcohol at all and save yourself from the trouble.

Installing Anti-Backfire Equipment

There is special equipment that is attached to many mowers that prevent backfiring when the mower is shut down. These are called anti-after-fire solenoids. It is a great idea to install them that let you turn the engine off irrelevant of the speed and do not let the fuel shoot the muffler.

Final Thoughts

It sounds dangerous when your engine makes a popping sound. However, this is not something that you should be bothered about. Using the information provided above, you can figure out what caused the mower to backfire and then follow the recommended fix. It is however important to act fast to not cause any permanent damage to the mower.

However, if you have been noticing issues with your lawn mower for a long period, then read this article to know if you should repair or replace your mower: When to Replace Lawn Mower Or Should You Just Repair?

Lawn Mower Engine Surging – Check this easy fix first!

Lawnmower engine surging is a right pain in the Jacksie; it’s an engine that runs erratically and revs up and down by itself uncontrollably. In some cases, it may only happen under certain conditions, for example, only after the mower gets hot or only when the fuel level gets low.

So what causes the lawnmower engines to surge? The most common reason for a surging lawn mower engine is a blockage in the fuel supply, but there are other possibilities:

Often you’ll find playing around with the throttle helps or applying some choke. You are not on your own; this is a regular complaint. In this guide, we will cover the diagnosis, likely causes, and solutions.

Try the easy fix first – replacing/cleaning gapping the spark plug before attempting carburetor work. If your mower engine is a Honda or Kohler, the fix is simple. Honda and Kohler’s surging is commonly caused by a blocked idle jet see “Gas starvation” towards the end of the page.

If you need more help, check out the “How to fix a surging mower video.”

If your surging mower is a Honda, check out the “Honda mower surging video.”

For many mowers, the fix is to replace the carburetor, and as carburetors are inexpensive, it just makes sense to swap it out and save a ton of messing around. You can check out the quality carburetors available and conveniently delivered to your door by Amazon.com.

Need more info on the fuel system, carburetor components, and how they work, you can check them out here.

Briggs Stratton Surging

Surging BS Classic 450, 500, or 550Some engine types are famous for surging; the Briggs Stratton 450, 500, and 550 series engines are fitted with a metal fuel tank and priming bulb-style carburetor. If you have one of these types of engines and it’s surging – You’re in the right place.

If you don’t have this type of carburetor, skip this section and jump to “Surging Test” below. These engines are fitted with a metal fuel tank and carburetor combination. The gasket sandwiched between the tank, and carburetor distorts over time, allowing a vacuum leak.

The vacuum leak causes the surging; replacing the gaskets and cleaning the carburetor/tank will leave it like new, I promise. In this tutorial, we’ll remove the tank/carburetor unit, clean it and replace the gaskets. Just some basic tools are needed, but get yourself a can of carburetor cleaner; it makes the job a lot easier.

In the workshop, I use WD40 carb cleaner, and you can check out all the tools and parts I use here on the “Small engine repair tools” page.

Tools You’ll Need

Here’s a short list of tools you’ll find useful to complete the task of fixing your surging mower. These tools aren’t essential, but they do make the whole job a ton easier; you’ll need:

Fuel treatment – Every small engine owner should use gas treatment. Most people don’t know gas goes off, and gas left in small engines can cause real problems, as you already know.

Using a gas stabilizer will keep the gas in your mower and your gas can fresh for up to two years.

Carburetor gasket – If you’re fixing the BS Classic engine, then you’ll need this gasket set.

Complete carburetor – As an alternative to replacing your BS Classic carburetor gasket, replace the complete carburetor instead; it includes the replacement gasket.

Manifold – This will only be needed if you have confirmed it has failed. Note there are a few different types of manifold pipe, so be sure to check before ordering.

You can check out all these tools on this page “Carburetor Surging Repair Tools.”

This carburetor style is fitted to a few engines and is prone to gasket failure. The job of replacing is simple and will solve the surge. The process is as follows:

Remove the spark plug wire – prevents the mower from starting.

Remove – Remove and clean the air filter and filter housing – Clean it using soapy water, and when dry, smear some engine oil over the surface of the foam. This helps trap dirt.

Remove tank bolts – They hold the fuel tank to the engine.

With fuel tank bolts removed – pull the tank unit straight out gently and remove the governor control link.

Remove the black rubber elbow crankcase breather pipe. Remove the manifold seal and keeper ring. Sometimes they will come loose and get stuck on the manifold pipe.

Remove – Remove carb screws from the carburetor and set aside.

Using a can of carburetor cleaner – clean all the ports on the surface of the fuel tank.

Empty the tank and rinse it out with fresh gas.

Pull the Siphon from the carburetor; they can be stubborn. Remove both gaskets and use carburetor cleaner to clean the siphon metal filter and all ports of the carburetor. Check the primer bulb for damage; mice like to eat them.

Spray – Spray the carburetor with carb cleaner.

Remove – Remove old gaskets and discard them.

Careful of this spring; it lives under the gaskets, and it can drop off and be tricky to find, as I know only too well.

The gasket is a two-part kit; the rubber-type gasket faces the tank. (carb fitted here for demo only)

The Siphon pushes back into the carb with a click. If you don’t hear the click, it’s not right – try again.

Refit the carburetor to the tank. Don’t over-tighten the screws, as this will distort the gasket. Fit manifold seal and keeper. Smear a small amount of oil on the seal; it helps it seat.

Clean the intake manifold. The grey tube in this shot is manifold. Inspect it for any signs of damage; they are prone to cracking. This will also cause a surge.

To fully inspect the pipe, you need to remove the pull assembly.

I would only do this if there was obvious damage to the manifold or if I had replaced the carburetor gasket and the engine was still surging.

This manifold is cracked and will cause a surge.

Before refitting the tank, fit the keeper ring and O-ring seal. Lube the seal before refitting the gas tank.

Offer the carb/tank unit up to the manifold and attach the governor link and spring. Now push the unit firmly onto the manifold. Fit both bolts.

Refit the air filter and spark plug wire. Use only fresh gas; make sure your gas can is clean. Gas older than three months is stale.

If, after fitting the gaskets, you still have a surge – Replace the Manifold.

Surging Test

As you know, gas starvation causes an inconsistent flow of fuel which in turn causes erratic running. And you also know a vacuum leak will cause erratic running, but it is a much less common cause; however, some carburetors are prone to vacuum leaks.

As engine manufacturers strive to make their engines more efficient, they have also made the carburetors more likely to clog; this has become a common issue.

To quickly diagnose which problem you have, a clogged carb or vacuum leak, follow this simple test.

You will need a helper to hold the bail lever or improvise with duct tape. CAUTION careful where you place your fingers and toes; the engine will be running, so the blade will be spinning.

Your mower will have a Manual choke, Auto choke, or a Primer bulb. Identify which type your mower has; the test is slightly different for each.

If you have a manual choke – apply half choke with the engine running.

If the engine now runs without surging – Gas starvation is the likely fault. If it runs just the same – A vacuum leak is a more likely fault.

If you have an Auto choke – Remove the air filter cover and filter – place a clean rag over the intake while the engine is running.

If the engine now runs without surging – Gas starvation is the likely fault.

If the engine runs just the same – A vacuum leak is the more likely fault.

If you have a primer bulb – you can still do the test – while the engine’s running (need a helper); give it some extra gas by pressing the bulb.

If the engine now runs without surging – Gas starvation is the likely fault.

If it runs just the same – A vacuum leak is a more likely fault.

Gas Starvation

If the test revealed gas starvation, it also showed that your problem is likely a dirty fuel jet in the carburetor, or the gas may be stale or contaminated by water.

Cleaning the main jet usually does the job.

lawn, mower, backfires, engine

Idle Jet Surging – Honda and Kohler use a relatively easy-to-access idle jet that clogs up and causes surging. The Kohler is easier to access than the Honda.

The Kohler is easier to access than the Honda.

Briggs has fitted a plastic carburetor to a range of engines which also clog up and cause surging.

All of these carburetors can be repaired by cleaning, which I’ve covered previously in videos (links below). Videos cover step-by-step removal, cleaning, refitting, and adjusting your carb.

Fixing this is not difficult. Sometimes you can get lucky by just draining and cleaning the gas bowl, which only takes a few minutes.

I have written a complete guide to Carburetor cleaning with pictures; it includes the gas bowl clean-out, which, as said, is worth trying first.

If cleaning doesn’t work out for you, go ahead and swap out the carburetor for a new one. Check out “New lawn mower carburetors page,” here, I’ve listed good quality replacement carburetors for all the most popular engines.

Carburetors aren’t expensive; messing around with them doesn’t make sense.

You might find this page helpful too – “Carburetor repair tools” I’ve listed some really useful tools that make the job easy. Some of these tools I’ll bet you already have some.

But do try cleaning the gas bowl before removing the carburetor.

Finding a Vacuum Leak

Air that enters the combustion chamber without passing through the carburetor is un-metered. This means the fuel-to-air ratio is unbalanced and, in turn, causes erratic engine performance.

When air sneaks in like this, it causes the engine to run lean (lacks gas). A lean engine runs hot, which isn’t good for an engine, especially an air-cooled one.

Vacuum leaks usually occur because of damaged gaskets. Gaskets are sealing materials fitted between the mating surfaces of engine components. Their function is to create an airtight seal.

They are commonly made from paper, felt, cork, Teflon, neoprene, metal, and rubber. The material type is dependent upon where the gasket is to be used.

Gaskets wear out and break down, and that causes surging.

Extreme Caution – You need to be careful, the engine will need to be running, and so the blade will be spinning when running this test.

A vacuum leak check is performed with the engine running and a can of carburetor cleaner; WD40 works, too, (is there anything WD can’t do?)

Spray the cleaner around all carburetor gaskets anywhere the carburetor meets the engine. The trick is to hear an instant change in engine note; that’s the sign of a vacuum leak.

This can be challenging; you must train your ear to notice the instant change in engine note (and not the surging).

Just do a small section at a time; this will allow you to pinpoint the failure area. Jumping the gun and replacing gaskets without finding the actual leak may work out for you or leave you with the same problem after the rebuild.

You’re right in thinking carburetor gaskets usually cause the problem, but other components, such as manifold pipes, can crack or become loose, causing surging.

Mower Backfires while trying to start it. Easy fix.

Fixing A Vacuum Leak

If a leak is detected, replace all carburetor gaskets, and as you have the carburetor removed, go ahead and clean it. Replacement gaskets are available online; you will require the make and model numbers from the engine.

All manufacturers will have a model number printed on a sticker placed on the body or on the engine. Have a poke around; you’ll find it. Most engine manufacturers will stamp the model numbers in an accessible area. Briggs Stratton stamp their numbers on the metal engine cover.

A new carburetor comes with new inlet gaskets; I like to fit original parts where I can; they fit and are guaranteed.

If, after replacing the carburetor gaskets, the engine still surges, you’ll need to go a little further and replace the manifold intake and gasket.

It’s not a big job, and they don’t give a lot of trouble, but they do crack as they get older. I wrote a step-by-step guide showing you everything you need to know – “Briggs Manifold Replacing.”

Related Question

Honda lawn mower surging fix? To fix a surging Honda lawn mower engine, clean the carburetor, gas tank, and fuel filter. Use fresh regular gas or e10. What causes a lawnmower to run slowly? The most likely cause is a throttle linkage bent out of shape by bumping into the shrubbery or a throttle spring has detached itself.

Hey, I’m John, and I’m a Red Seal Qualified Service Technician with over twenty-five years experience.

I’ve worked on all types of mechanical equipment, from cars to grass machinery, and this site is where I share fluff-free hacks, tips, and insider know-how.

And the best part. it’s free!

Why Does My Honda Lawn Mower Backfire?

This post may contain affiliate links. As an affiliate of retailers(like Amazon), we earn from qualifying purchases.

When it comes to lawn mowers, Honda is among the most popular brands in the business. Occasionally during use, you might find that your Honda lawn mower backfires. A backfire is a pop or loud boom that occurs when gasoline ignites outside the engine’s combustion chamber; so, what causes a Honda lawn mower to backfire?

A lawn mower backfires when burning fuel enters the exhaust or the engine. This happens when s of unspent gasoline enter the engine or exhaust system before the valves close. Backfires occur due to Rapid deceleration, faulty components, and even incorrect fuel blend, among other causes.

Want to know more about why your Honda lawn mower is backfiring? Read on as we discuss proven ways to fix a backfiring lawn mower.

Causes of Engine Backfires in Lawn Mowers

Below are some of the leading causes of backfiring in Honda lawn mowers.

Decelerating Too Fast

Lawn mower backfires mostly occur during Rapid deceleration when the engine attempts to align its timing with the lowered throttle. In most cases, this tends to lead to excessive air in the mix, which in turn creates a lean blend. The lean blend is consequently forced into the lawn mower’s exhaust system, where it makes the infamous pop sound when it combusts.

Slowing down a small engine should be gradual. Therefore, if your Honda lawn mower is backfiring when you’re looking to shut it off, chances are you’re decelerating too fast. The engine speed increases when using a lawn mower, and shutting it abruptly means the engine could pump some stray gas into the muffler, which could lead to combustion.

To prevent backfires when turning off your Honda lawn mower, reduce the mowing speed gradually, and allow the motor to idle for roughly 20 seconds before turning it off.

Fuel Blend

Fuel blend is a crucial aspect to consider when dealing with small engines. You’ll find that some gasoline contains ethanol or alcohol as part of the fuel blend, which can prove troublesome over time. Most Honda lawn mowers struggle to burn this blend effectively, which often results in power loss and occasional backfires.

Since lawn mowers are designed to handle specific blends of gasoline, using a wrong blend can lead to system imbalances. Due to this, it is advisable to use gas containing zero alcohol levels. If zero-alcohol blends are hard to come by, go for blends that contain low levels of alcohol.

Water Contamination

Water is another major cause of backfiring and loss of power in mowers. To remove water from your Honda lawn mower, you’ll need to start by removing the spark plug. Afterward, carefully remove the carburetor and clean it thoroughly. You should also check on the combustion chamber’s moisture levels before adding some fresh engine oil to coat the walls of the piston chamber.

Water contamination is a serious problem that, if not addressed early enough, can lead to long term damage to fuel lines, the tank, and carburetor.

Lean Carburetor

The carburetor is crucial to the functioning of a lawn mower as it regulates the volume of gas and air required for combustion. The balance must be perfect for proper combustion. While some Honda carburetors come with an electrical solenoid to control fuel flow, most come with two adjustment screws that are usually mounted on the exterior. One screw is for controlling the mix, while the other is for idle adjustments.

If the carburetor produces a lean mix, chances as the lawn mower will backfire during deceleration or even during normal operation. The good news is that carburetors are easily adjustable. However, consulting with a professional is advisable if it’s your first time attempting to adjust your Honda lawn mower’s carburetor.

Dysfunctional Valves

Valves are essential parts of a lawn mower that need to function correctly for successful outcomes. The valves help to seal off the firing chamber or cylinder of a small engine. One valve allows air and gas to make way to the cylinder while the other opens to allow the exit of exhaust gases from the cylinder.

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If one of the valves malfunctions (even for a second), then the lawn mower will backfire. But fixing valves on your own isn’t recommended since they are internal parts of your Honda mower. Consider outsourcing the valve repair job to experienced service professionals.

Damaged Spark Plug

A damaged or worn out spark plug will create a weak spark that might fail to ignite the cylinder. This means that instead of igniting in the cylinder, the fuel might ignite once it reaches the exhaust muffler, which results in a backfire.

Also, an incorrectly set gap between the spark plug’s electrodes tends to result in weak sparks that make the mower unreliable. Replacing the spark is necessary if your Honda lawn mower is backfiring as a result of weak sparks.

Poor Airflow in the Engine Area

When the engine runs at a higher than normal temperature, your Honda lawn mower might gradually start to backfire. This explains why most lawn mowers require enough space in the engine housing to allow for adequate airflow.

Your engine needs enough air circulation for it to cool. Therefore, besides turning off the engine and allowing it to rest, you can consider modifying the engine’s housing to improve air circulation inside the mower.

Damage to Internal Components

Your Honda lawn mower shouldn’t backfire when starting, and if it does, then one or two components are not functioning correctly. You’ll find that a broken flywheel often leads to stuttering or backfiring when attempting to start a mower.

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Luckily, the more sensitive areas of a lawn mower, such as the crankshaft, are usually surrounded by their inexpensive counterparts that cost a lot less to repair. Therefore, if your Honda lawn mower is backfiring when starting, you’ll need to call in a professional to identify and repair the damaged components.

How to Keep Your Honda Lawn Mower From Backfiring

Avoid Cutting Wet or Damp Grass

Mowing the lawn when the grass is wet or damp can damage your mower, consequently leading to long term problems. As mentioned earlier, you should remove water once you suspect either the tank or carburetor has been contaminated.

Read the User Manual Before Use

Lawn mowers function differently. Take enough time to read the instructions before putting your new Honda lawn mower to good use. Generalizing the function of different brands of lawn mowers can lead to backfiring or malfunctioning when wrongly used.

Clear Debris Before Mowing

Large stones, toys, twigs, and branches might damage your Honda lawn mower. Although most mowers come with adequate safety-enhancing features, exposing them to extra hard surfaces and conditions might lead to backfiring and even total damage.

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Check the Fuel Blend

Gasoline with high alcohol concentration is more likely to lead to backfiring compared to using pure gasoline. Go for fuels with little to no alcohol concentrations to eliminate the chances of backfiring due to fuel.

Final Thoughts

While it’s normal for lawn mowers to backfire every once in a while, you should always take your time to determine the cause of backfiring. Factors such as fuel blend and water contamination can gradually damage your yard-maintenance device, leading to serious defects.

Although backfires aren’t dangerous to the engine or users, the large pop noises can be annoying. And to prevent a backfire when you’re done mowing, be sure to turn off the mower gradually, specifically 15-20 seconds after the blades have come to a halt.

Remember, since backfires tend to indicate underlying issues with your mower, you should consider reaching out to an expert if you can’t determine the cause(s) of backfires.

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