Honda mower engine surging. Is Your Lawn Mower Surging? Here’s the One Simple Fix You Need

Is Your Lawn Mower Surging? Here’s the One Simple Fix You Need

Do you have a surging lawn mower that’s acting up? I’ve been there too and discovered that the most common cause is a blockage in the fuel supply. In this blog post, we’ll dive into other factors causing your “lawn mower engine to surge at full throttle“, as well as providing practical steps on how to remedy these issues.

Stick around for an enlightening journey through the world of lawn mowers!

Key Takeaways

  • The most common causes of a surging lawn mower engine include poor gas quality, a clogged fuel cap vent, and a dirty fuel filter.
  • Poor gas quality can lead to irregular combustion in the engine, causing it to surge. It is important to use high-quality gasoline to prevent this issue.
  • A clogged fuel cap vent disrupts the flow of fuel to the engine and can result in surging. Regularly cleaning the vent is crucial for smooth operation.
  • A dirty fuel filter can cause fluctuations in fuel flow, leading to surges. It is recommended to replace the filter regularly for optimal performance.

Causes of Lawn Mower Surging

There are several causes for a lawn mower engine to surge, including poor gas quality, a clogged fuel cap vent, and a dirty fuel filter.

Poor gas quality

Stepping out onto your lawn, you find that your faithful lawn mower is surging. And it’s not due to some mechanical wizardry; instead, it could be as simple as the quality of gas you’re using.

In fact, poor gas quality is a common culprit when a lawn mower engine starts surging at full throttle. Here’s why: low-grade gasoline can lead to irregular combustion in the engine because it degrades faster and may even become contaminated over time — this contamination might be from water condensation or other pollutants.

Now imagine trying to run with one shoe on, awkward right? That’s how your lawn mower feels running on degraded gasoline – its pace fluctuating up and down unevenly like an unsteady jogger.

This irregularity prompts what we call ‘surging’. over, if old or unprotected fuel has idled in your machine for too long, don’t be surprised if this triggers surges too.

So next time think twice before filling up with any ol’ gas – Your choice of fuel can essentially make or break the smooth operation of your beloved landscape companion! To keep those unwanted engine hiccups at bay and ensure a seamless mowing experience each time – opt for premium-quality gasoline whenever possible.

Clogged fuel cap vent

Imagine this: Your lawn mower engine is surging, revving up and down as if it has a mind of its own. You’re not alone; many unsuspecting homeowners face this issue. Allow me to explain one potential cause – a clogged fuel cap vent.

Most lawn mowers have tiny vents on their fuel filler caps. These vents play an essential role in maintaining the correct vacuum and pressure inside the fuel tank, ensuring your lawn mower runs smoothly without any annoying stuttering or surging.

But sometimes, dirt or debris can block these little vents, disrupting the steady flow of fuel to your engine. The result? Your once reliable lawn mower engine surges at full throttle.

The situation gets worse when there’s improper back pressure in the fuel tank due to a clogged vent causing the gasoline pressure to oscillate between extremes resulting in noticeable fluctuations – effectively making your lawn mower engine surge up and down.

That said, keeping your fuel cap vent clean is crucial for a smooth-running machine! Just like regular oil changes and spark plug replacements, cleaning out this tiny but mighty component should be part of your routine maintenance checklist.

After all, who wants their serene Sunday morning disrupted by a surging lawn mower?

So next time you notice that familiar lull-and-roar pattern indicating your lawn mower is surging again, do check if it’s just another case of dirty fuel cap vent before diving into other possible causes.

Dirty fuel filter

Owning a lawn mower, you’re likely familiar with the engine surging and how disruptive it can be. One common culprit is a dirty fuel filter. This unassuming component plays a critical role in maintaining your lawn mower’s performance by ensuring only clean fuel reaches the carburetor.

Over time though, dirt and debris can clog this filter, disrupting the steady flow of gas from the tank to your lawn mower engine which causes it to surge up and down at full throttle.

That hiccuping or stuttering sensation you feel? It’s often tied directly back to this issue! To fix this, simply replace your old fuel filter with a new one; an easy task that enhances proper functioning of your machine while minimizing instances where your lawn mower is surging due to blockage in its fuel system.

Solutions to Fix Lawn Mower Surging

To fix a surging lawn mower, start by removing any bad gasoline from the fuel tank. Then, clean the fuel cap vent to ensure proper airflow. Finally, swap out a dirty or clogged fuel filter with a new one.

Removing bad gasoline

If you notice your lawn mower surging, one possible culprit could be bad gasoline. Using old or contaminated gas can cause engine surges, often due to water condensation. To address this issue and get your lawn mower running smoothly again, follow these steps:

  • Drain the existing gasoline: Begin by safely draining the old gas from your lawn mower’s fuel tank.
  • Locate the fuel line: Find the fuel line that connects the tank to the carburetor.
  • Disconnect the fuel line: Carefully disconnect the fuel line from either end, taking note of its position for reattachment later.
  • Prepare a container: Place a clean container or gas can under the disconnected fuel line to catch any remaining gasoline.
  • Drain the remaining gas: Tilt your lawn mower so that the remaining gasoline flows out of the fuel tank and into the container.
  • Dispose of old gas properly: Once all the old gas has been drained, dispose of it properly according to local regulations or guidelines.
  • Clean out the fuel system: With fresh fuel now needed, make sure to thoroughly clean out any debris or residue in your lawn mower’s fuel system.
  • Refill with fresh gasoline: Fill up your lawn mower’s tank with fresh, high-quality gasoline.
  • Reattach and secure the fuel line: Reconnect the previously disconnected fuel line securely to both ends – ensuring a tight fit and no leaks.

Honda Mower Crazy RPM Fix. Simple!

Cleaning the fuel cap vent

Cleaning the fuel cap vent should be done regularly to prevent surging in your lawn mower engine. Here’s how to do it:

  • Remove the fuel tank cap from your lawn mower.
  • Inspect the cap for any debris or dirt that may be blocking the vent.
  • Use a small brush or cloth to gently clean the vent, ensuring that it is free from any obstructions.
  • If the vent is still clogged, you can use compressed air to blow out any remaining debris.
  • Once the vent is clean, carefully reattach the fuel tank cap to your lawn mower.

Swapping out a fuel filter

One of the solutions to fix a surging lawn mower engine is by swapping out the fuel filter. A clogged fuel filter can cause issues with the flow of fuel to the carburetor, leading to fluctuating revving and surging of the engine. If you notice your lawn mower surging at full throttle or the engine surging up and down, it may be time to replace the fuel filter.

  • Improved Fuel Flow: A clogged fuel filter restricts the flow of fuel to the carburetor, affecting its performance. By replacing it with a clean one, you ensure a steady flow of fuel without any interruptions.
  • Enhanced Engine Performance: When the carburetor receives a consistent supply of clean fuel, it can mix it properly with air and provide smooth combustion. This leads to better engine performance and reduced surging.
  • Prevention of Damage: A clogged fuel filter can lead to harmful particles or debris reaching sensitive components such as valves or injectors. By swapping out the filter regularly, you protect these vital parts from potential damage.
  • Reliable Operation: A new fuel filter ensures that only clean fuel enters the carburetor and other engine parts. This helps prevent sudden stalling or erratic behavior during operation.


In conclusion, if you find that your lawn mower is surging, there are several potential causes to consider. Poor gas quality, a clogged fuel cap vent, and a dirty fuel filter are common culprits.

Fortunately, these issues can be resolved by removing bad gasoline, cleaning the fuel cap vent, and swapping out a fuel filter. By addressing these underlying problems, you can ensure that your lawn mower operates smoothly and efficiently.


What causes a lawn mower to surge?

A lawn mower can surge due to a variety of reasons, including clogged fuel lines or filters, a dirty carburetor, an improperly adjusted throttle, or issues with the spark plug.

How can I fix a surging lawn mower?

To fix a surging lawn mower, you can start by cleaning or replacing the air filter and spark plug. Check for any debris in the fuel line and clean or replace it if necessary. If the issue persists, you may need to clean the carburetor or adjust the throttle settings.

Can bad gasoline cause my lawn mower to surge?

Yes, bad gasoline can contribute to your lawn mower surging. Old or contaminated gasoline can lead to clogs in the fuel system which disrupts proper engine performance.

Should I seek professional help if my lawn mower continues to surge after troubleshooting?

If your best efforts at troubleshooting have not resolved the surging issue with your lawn mower, it is recommended to seek professional help from a qualified technician who specializes in small engines. They will be able to diagnose and repair any underlying problems accurately and efficiently.

Mower Engine Surging at Idle and How to Fix

Engines for lawnmowers are designed to be dependable and effective at cutting grass and keeping a tidy lawn. Even the greatest lawnmowers, nevertheless, are susceptible to engine surging at idle, which can cause the engine speed to constantly swing up and down.

Multiple factors could be the root of this issue, including:

After viewing this article, mower owners will quickly understand what causes Mower Engine Surging at Idle and how to resolve the problem.

Reasons Why Mower Engine Surging at Idle (Solutions Added)

This section will examine common causes of engine surging:

Clogged Air Filter

A lawnmower engine can surge when the air filter is blocked because it restricts the airflow to the engine. The engine is unable to receive the air it requires to burn gasoline effectively when the air filter is blocked with debris, dirt, or grass clippings.

This may lead to an excessively high fuel mixture, which makes the engine run rich or lean and results in surging.

mower, engine, surging, your, lawn

It is to note that the engine uses less fuel when it is idling since it is operating at a reduced pace. The engine won’t receive enough air to burn fuel effectively at idle if the air filter is clogged.

As a result, the engine may struggle to maintain a constant idle speed and experience ups and downs in speed. A clogged air filter can also make the engine stall or run erratically, especially while accelerating or under load.

Fix: Examine the air filter

It’s critical to routinely check the air filter and clean it or replace it to avoid surges brought on by a clogged air filter. By performing this, you can be convinced that the engine is getting enough air to idle smoothly and burn fuel effectively.

Old or Defective Carburetor

An out-of-date or damaged carburetor may not be providing the right amount of air and fuel to the engine, which might result in a lawnmower motor surging at idle.

Regulating the flow of fuel and air into the engine is the carburetor’s responsibility to ensure effective combustion. Surging could occur if the carburetor can’t carry out this task adequately due to wear or corrosion.

over, a precise amount of fuel and air at idle to keep the speed constant is important for the engine to run. The engine may receive too much or too little fuel if the carburetor isn’t working properly, which might cause the engine to surge.

The engine may run excessively richly or too leanly as a result, which can result in additional problems including stalling, harsh running, or trouble starting.

Fix: Check the carburetor

Checking the carburetor is important when the engine is surging. It can be necessary to clean, repair, or replace the carburetor to address surging which occurs because of an outdated or malfunctioning carburetor.

A trained mechanic should perform this technique because it can be difficult. You can easily avoid carburetor faults with regular carburetor maintenance, which includes cleaning and tuning.

Faulty Spark Plug

A lawnmower engine might surge at idle due to a malfunctioning spark plug because it can disrupt the process of ignition.

For the engine cylinder’s air-fuel mixture to ignite and generate power, a spark plug must be present. Surging may occur if the spark plug is defective because it isn’t regularly igniting the fuel mixture with a strong enough spark.

A steady spark at idle plays a great role in the engine to keep its speed stable. The engine may malfunction or run erratically if the spark plug fails, which might cause surging.

A faulty spark plug might also result in additional problems like difficult starting, harsh running, and reduced engine output.

Fix: Replace the spark plug

You may learn the importance of using the proper spark plug for the mower and proper gapping by checking the spark.

Simply execute regular checks on the spark plug, which includes cleaning and replacement at the proper intervals, to avoid the problem of surging and other challenges caused by spark plug concerns.

Loose or Damaged Fuel Lines

Due to their ability to alter the flow of fuel to the engine, loose or damaged fuel lines may result in a lawnmower engine that surges when it is idling.

mower, engine, surging, your, lawn

The fuel lines are in charge of transporting fuel from the fuel tank to the carburetor, and then to the engine. Fuel pressure may drop as a result of broken or faulty fuel lines, which may lead to surging.

Not to forget that the engine needs a specific amount of gasoline at idle to keep its speed consistent. Fuel pressure may drop and surging may occur if the fuel lines are broken, cracked, or loose and are admitting air into the fuel system.

Fix: Verify the fuel lines

It may be necessary to inspect and replace the fuel lines if necessary to correct surges caused because of loose or damaged fuel lines.

It’s crucial to utilize the proper gasoline line type for the mower and to make sure the fuel lines are attached correctly and are not broken or kinked.

Finally, Adjust the idle Speed

One way to resolve a lawnmower engine surging problem is to change the idle speed. The pace at which the engine runs while it is in neutral and not actively mowing is referred to as the idle speed.

If a lawnmower engine surges or stalls at idle, it may be running too quickly or too slowly.

You must locate the carburetor’s idle speed adjustment screw to change the idle speed. You might need to refer to your lawnmower’s handbook to properly identify this screw, which is typically found on the side of the carburetor.

Cost to Fix Mower Engine Surging at Idle Issue

The price of a new air filter can vary from 5 to 25, depending on the retailer where you purchase the replacement filter, and the brand and model of the mower also play a role here.

Depending on the brand and model of your lawnmower and the labor rates charged by the repair shop, the cost of cleaning the carburetor might range from 50 to 150.

In general, a new spark plug costs 5 to 15. There won’t be any additional labor charges if you feel confident changing the spark plug yourself.

If you intend to repair or replace a damaged fuel line, the cost will be determined by the extent of the damage and the cost of new parts. Replacement fuel lines usually cost between 10 and 50.

Remember that these are merely estimates and that final costs may differ based on a variety of elements, including your location, the scope of the required repairs, and the repair facility you select.

mower, engine, surging, your, lawn

Maintaining a beautiful lawn can be a daunting task, especially if you lack the appropriate know-how and tools to handle the challenges that may crop up. Fortunately, LawnAsk is here to offer you an all-encompassing resource that covers everything you need to know about lawn care.

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A smoking lawn mower is never a good sign. Whether the smoke is blue, white, or black, here’s how to identity and address the issue without the help of a professional.

By Glenda Taylor and Bob Vila | Updated Sep 24, 2020 1:40 PM

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Q: Recently, my mower started billowing smoke when I powered it up, so I shut it off immediately. Why is my lawn mower smoking? And is it a fire hazard? I want to know how to proceed so I don’t harm the machine.

A: Your lawn mower can emit smoke for numerous reasons—many of which don’t require the services of an expert. A homeowner can usually identify the reason for a smoking lawn mower by gauging the color of the Cloud coming around the engine, then fix it accordingly before lasting damage occurs. Keep in mind that all mowers with internal combustion engines contain the same basic parts, but the configuration of those parts varies widely, depending on manufacturer and model. Consult your owner’s manual if you’re unsure how to access a specific part of your lawn mower’s engine.

White or blue smoke may indicate an oil spill on the engine.

If you’ve recently changed the oil in your mower and the engine is emitting white or blue smoke, it’s possible that some of the oil spilled onto the engine. Similarly, you could’ve spilled oil on the engine by mowing on a slope greater than 15 degrees or tipping the mower on its side. The smoke may look disconcerting, but it’s completely harmless. Solve the problem by restarting the mower and allowing the spilled oil to burn off. If you tip the mower often for cleaning or maintenance, check your owner’s manual to determine the best way to reduce the risk of oil leaks.

An overfull oil reservoir may also cause white or blue smoke.

Ensure you didn’t overfill the mower by checking the oil level with the dipstick located on the reservoir. To do this, remove the dipstick cap, wipe off the stick with a rag, and reinsert it into the reservoir. Then remove the dipstick once again and determine the oil level in comparison to the recommended “fill” line on the stick. If the level is too high, drain the oil (consult your owner’s manual for instructions), then refill the reservoir with it. Start checking the oil level with the dipstick after you’ve added about ¾ of the amount recommended in the manual. Continue to add small amounts of oil until the level matches the recommended “fill” line. Also note that using the wrong grade of engine oil may cause blue or white smoke. Consult the owner’s manual for the exact type of oil recommended for your mower.

Black smoke may indicate that the mower is “running rich,” or burning too much gasoline.

Your lawn mower’s carburetor regulates the ratio of gasoline to air mixture. If the carburetor isn’t getting enough air, the mixture has a higher percentage of gasoline, which can create black exhaust smoke. It’s possible that a dirty or clogged air filter is preventing sufficient airflow into the carburetor. Try replacing the air filter. (Note: air filters vary by mower model; view example air filter on Amazon.) Next, run your lawn mower for a few minutes. If the black smoke still appears, the carburetor might need to be adjusted in order to increase airflow. Either take the mower to a professional or adjust the carburetor yourself with instructions in your owner’s manual.

Take your mower to a repair shop if necessary.

If the previous steps don’t correct blue or white smoke, your mower could have a more serious problem, such as an air leak in the crankshaft (the cast iron or cast aluminum case that protects the moving parts of a mower’s engine). Continuing blue or white smoke could also indicate that some of the engine’s components or seals are worn out and need replacement. Similarly, if black smoking still persists after you’ve replaced the air filter and adjusted the carburetor, you could be facing a more serious mechanical issue. All of these problems require the help of a professional. If your mower is still under warranty, check with the manufacturer for the location of the nearest servicing dealer; problems stemming from a factory defect or poor workmanship may garner free repairs. If your mower is not covered under warranty, a reputable small-engine repair shop should also be sufficient to get the job done.

What causes lawn mower engine surging?

Fuel system problems or vacuum leaks through the air intake manifold are typical causes of lawn mower surges.

Here’s a rundown of the specific issues causing small engines to quickly cycle between idle speed and full throttle:

  • Contaminated gasoline. Old gas or gasoline contaminated with water can cause engine surging.
  • Clogged fuel tank cap vent. The fuel tank cap vent can get clogged with dirt or debris. The fuel cap vent helps keep gas flowing smoothly to the carburetor. When it’s clogged, the engine can surge.
  • Dirty air filter. The carburetor won’t get a good supply of air when the air filter gets clogged with dust and dirt.
  • Worn or damaged air intake gasket. The mower surges when the carburetor sucks air through an unsealed gap in the air intake manifold instead of through the air filter.
  • Dirty carburetor. Clogged fuel jets inside the carburetor commonly cause the lawn mower engine to surge. Clogged jets can’t provide the right mix of air and fuel to the engine.

Troubleshooting a lawn mower that is surging

To find the cause of a surging engine, first check the basic issues described above.

  • If fuel in your mower’s gas tank is older than six months or you left the lawn mower out in the rain, move the mower to a well-ventilated area and drain the tank. If you see water in the drained gas, you’ll also need to remove the bowl from the bottom of the carburetor and dispose of that gas.
  • Check the air vent on the fuel tank cap. Clear the vent hole if it’s clogged.
  • Replace or clean the air filter if it’s dirty.

If these basic troubleshooting tips don’t help, then you’ll likely need to make one of the repairs described below.

mower, engine, surging, your, lawn

How do you fix a pulsating lawn mower?

Move the lawn mower to a well-ventilated area and take these steps to fix the engine.

  • Remove the air filter and its housing. Check the air filter housing gasket and replace that gasket if it’s worn or damaged.
  • If that gasket is okay, check the gasket and seals between the carburetor and the engine. Replace any worn or damaged seals or gaskets.
  • If external carburetor seals and gaskets are okay, then you’ll need to rebuild or replace the carburetor. Replacing the carburetor is a much easier repair that rebuilding the carburetor. Follow the steps in our How to replace a lawn mower carburetor repair guide/video to install a new carburetor. If the replacement carburetor for your engine is unavailable, or if you prefer to rebuild the carburetor, order the rebuild kit for your carburetor and follow the steps in our How to rebuild a lawn mower carburetor repair guide/video to clean and rebuild the engine’s carburetor.

How much does fixing a surging lawn mower engine cost?

If you can troubleshoot the surging engine and don’t have to buy parts, the cost of fixing your lawn mower typically isn’t more than the price of replacing the gas.

If you have to buy parts such as an air filter, carburetor or carburetor rebuild kit and you complete the repair yourself, the cost of fixing a surging lawn mower won’t be much more than the cost of the repair parts. The most expensive part that you would have to buy would be the carburetor. You’ll pay about 50 for the replacement carburetor on many common lawn mower engines.

When you have to take the lawn mower to a repair shop to get it fixed, then the repair will typically cost between 50 and 100 to fix a surging engine.

Why is My Lawn Mower Engine Surging?

Imagine you are mowing your lawn on a typical sunny Sunday. You are halfway there and look behind to appreciate the evenly laid out grass. But as you continue to mow the remaining of the lawn, you start noticing your lawn mower engine surging. The lawnmower surge is too little to start with at the beginning. However, as you continue the mow, the surge starts getting stronger.

The one thing you don’t want your engine to make is noise, in many cases those noises could be due to lawn mower backfiring. Although you have opted for a noise-free lawn-mower in the first place, you notice your lawn mower engine surging. Noising out an engine cause concern and must be addressed immediately. So, if you hear your lawn mower engine surging, then we are here for you. This article will walk you through all the possible causes that contribute to a lawnmower surge. Finally, we will lay down some easy fixes you can implement to tackle this issue.

Causes Of Lawn Mower Surging

Knowing the probable cause behind your lawn mower surging is key to going ahead. Once you have known all the probable causes behind the issue, it becomes relatively easier to tackle the problem the next time it arises. One of the primary causes behind a lawnmower engine surge is a blockage in the fuel supply. If your mower is subject to regular use, dust or other particles may tend to enter the engine and block the fuel supply. But apart from the fuel supply blockage, here are some other probable causes that can contribute to the lawnmower engine surge

  • Poor Quality Of Fuel
  • Malfunctioning Spark Plug
  • Faulty Carburetor (Find where it is)
  • Blocked Gas Filter
  • Blocked Fuel Tank
  • Blocked Gas Line
  • Gasket Vaccum Leak
  • Manifold Vaccum Leak
  • Governor Control Fault
  • Dirty Or Blocked Air Filter

Conduct A Surging Test

A surging test is perhaps the best way to determine any issues within your mower that need addressing. Primarily, a surging mower engine results from gas starvation or any other blockages that may have occurred within the fuel tank, air filter, or the fuel line. Meanwhile, some carburetors are prone to vacuum leaks, further intensifying the problem.

The majority of modern-day mower engines are designed for maximum efficiency. However, this has made the carburetors more prone to clogs and blockages. To quickly conduct a surging test, all you need to do is trace the given steps.

NOTE: You will need to have a helper to help you conduct this step

  • Make the helper hold the bail lever.
  • Ensure both of you are wearing protective gear such as earplugs, eye goggles, safety gloves, and safety boots
  • Identify the type of mower you have to know the type of choke it holds, namely manual, auto, or a primer bulb.

For Manual Choke:

How to stop your lawnmower from surging, or not starting, or starts then dies mower surges

  • Apply half choke with the engine running
  • If the engine runs surging, there is a lack of gas present
  • If there is no noticeable change in the surging, there is a vacuum leak

For Auto Choke:

  • Remove the air filter and housing
  • Place a clean rag over the filter and keep the engine running
  • If the engine runs surging, there is a lack of gas present
  • If there is no noticeable change in the surging, there is a vacuum leak

For Primer Bulb:

  • Add some extra gas to the engine by pressing the bulb
  • If the engine runs surging, there is a lack of gas present
  • If there is no noticeable change in the surging, there is a vacuum leak

How To Fix A Surging Lawn Mower?

Once you become familiar with the problem, it becomes relatively easier to tackle them. Similarly, you can always conduct a surging test to ensure everything’s in a good working condition and check whether all the fixes you have applied are implemented successfully. So, if you find your lawn mower engine surging, you can implement the following fixes.

NOTE: Before implementing either of the fixes,

  • Turn off your machine and allow it to cool off for at least an hour
  • Wear protective gear such as earplugs, eye goggles, and safety gloves
  • Do NOT touch anything with your bare hands
  • Do NOT touch the mower blades
  • Ensure that the machine is turned off at all times during the repair

Bad Fuel

This is one of the primary causes behind a lawnmower engine surging. If you live in an area where there isn’t a lot of rain, your mower is bound to be off at all times during the off-season. With the lawnmower, the engine fuel remains dormant during the period. This largely enhances the chances of the fuel getting contaminated. We cannot stress the importance of good fuel enough. You must fill the machine with the right kind of fuel.

The right fuel will only enhance your machine’s overall durability and longevity. Whereas subjecting your machine to bad or poor fuel quality will automatically take a tool on the mower’s engine. Know that gasoline is extremely important for appliances that run on fuel-injection technology, such as cars and lawnmowers. Gasoline is used to power up the engine by causing the combustion required for sparking. Good quality fuels will ensure a good fuel economy, smoother engine performance, higher engine power, and lower carbon emission.

Having your mower sit idle for long is likely to contaminate the fuel or the oil present. Hence, if you think the fuel is at fault, we suggest you empty the tank and refill it at once. To do so:

  • Tip-over your mower and drain away from the fuel and oil.
  • Ensure that NO COMBUSTIBLE OBJECT is present in the vicinity.
  • Once you have drained the fuel, fill the mower with fresh fuel.

Clogged Air Filter

Apart from the fuel tank, the air filter is the first thing you will need to check in case there is a surging lawnmower. The air filter is responsible for the regular supply of fresh oxygen to the mower engine. However, if the air filter is clogged, it starves the mower engine of fresh oxygen required for combustion. To check if the air filter is clogged, trace the given steps.

  • Disconnect the spark plug wire
  • Remove the air filter
  • Remove the air filter housing
  • Using soapy water, clean the foam filter
  • Once the cleaning is done, keep the filter to dry
  • Once the filter is dried up, smear an oil coating over the surface of the air filter.
  • If the filter is still dirty despite the cleaning, replace it with another filter that suits your model.
  • Wipe the dirt out of the filter before reinstalling it

Fuel System Issues

Just like bad fuel, fuel system issues are quite common when it comes to working with a lawnmower. Every fuel tank comes with a small cap that allows air to flow into the tank and mix with the fuel to ignite a spark and cause combustion. But just like air, dust, and dirt can sometimes flow through the cap and clog the fuel system preventing enough fuel from reaching the carburetor. To tackle this, implement the given steps.

  • Inspect the vent on your gas cap
  • If the vent is dirty, clean it
  • Drain the gas tank
  • Clean the gas bowl
  • Add a fresh batch of fuel to the tank
  • Alternatively, you can inject a fuel cleaner to clean the fuel line
  • Once all this is taken care of, run the mower to check if the issue is taken care of.

Dirty Carburetor

The carburetor is an integral part of every machine that runs on fuel-injection technology. The carburetor that allows the right amount of air-to-fuel rato into the engine is required to cause combustion. However, blockages within the carburetor are probably why you have a surging lawnmower. To eliminate this possibility, trace the given steps.

  • Disconnect the air filter
  • Disconnect the fuel tank
  • Disconnect the governor control link
  • Disconnect the breather pipe
  • Disconnect the manifold seal and the keeper ring
  • Finally, disassemble and disconnect the carburetor.
  • Use a carburetor cleaner to clean the carburetor thoroughly
  • If the carburetor is damaged, replace it at once
  • After cleaning the carburetor, reassemble the carburetor and reinstall it onto your mower.

Vacuum Leaks

A loose carburetor tends to suck in air through the crevices and traps it between the engine block. This will unbalance the air-to-gas ratio, compromising the vacuum required to transport fuel and air into the mower engine. All this collectively causes an irregular engine performance.

This is because a vacuum leak affects air and fuel rate flow through the carburetor at the recommended rate. A possible solution to fix a vacuum leak is to check the bolts on the carburetor and tighten them if necessary.

Spark Plug Issue

Lastly, the issue with the spark plug is probably your mower revs up and down. If you have an old or worn-out lawn mower, there are high chances of the spark plug being worn out. A worn-out spark plug may not have the strength to cause combustion and ignite the flame required for the mower to run. If you have a worn-out spark plug, you will find that your mower dies every other minute. A solution to this involves

  • Disconnect the machine
  • Remove the spark plug
  • Check the spark plug for any wear and tear
  • Check for the gap between the metal end and the protruding end of the plug
  • If the gap is too big or too small, adjust it accordingly to allow sparking to occur
  • Check to see if the mower is back to normal functioning

Any issue with the spark plug generally calls for a replacement. So, if you have little luck implementing this fix, we suggest you replace the spark plug with a new one designed for your mower.


Despite its impeccable architecture, a lawnmower is subject to various issues throughout its lifetime. One commonly reported issue is a surging mower engine, and the last thing you want to do is disturb your neighbors with a broken mower. Therefore, we suggest you look at our troubleshooting guide to help tackle the problem. However, if there is little to no luck in the fixes you have implemented, call in an expert to have a look at the machine at once.

Ulrich is a seasoned lawn and garden care expert with over 10 years of experience. He shares his practical tips and expert advice on various topics, including lawn maintenance, pest control, and landscaping, on BirdandFeather to help homeowners create beautiful outdoor spaces.

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