Lawn mower keeps revving. Here’s What To Do If Your Lawn Mower Won’t Start

Learn the reasons why a lawn mower won’t start after winter or during peak season, and how to fix those problems.

Family Handyman

Introduction

Most of the time when a lawn mower won’t start the cause is a problem with the gas or the lawn mower carburetor.

What to Do if Your Lawn Mower Won’t Start

Whatever kind of lawn mower you’ve got, the last thing you want once winter finally lifts and spring has sprung is a lawn mower that won’t start.

If you’ve taken the proper steps to winterize your lawn mower, you’re far less likely to be dealing with such issues. It’s also why you should tune up your lawn mower at the start of every season. However, it’s not out of the ordinary to find your gas-powered lawn mower not starting from time to time, so it’s important to know why your lawn mower isn’t starting and how to fix it.

Project step-by-step (6)

Check the Gas Tank

Let’s start with the obvious. Before you have a heart attack pulling on the rip cord, you’ll want to check the fuel. Like any gasoline-powered engine, lawn mowers run out from time to time. Maybe you forgot it was running on fumes when you finished mowing last time. It sounds simple, but we’ve all overlooked the gas tank from time to time.

Even if there is gas in the mower, if the fuel’s been in there more than a month, that could be the problem. Gas sitting around too long in the tank can get contaminated with dirt and extra moisture.

So if your gasoline has been in the mower for more than month, drain the gas properly, dispose of it correctly, and fill up the mower with new gas. It may take quite a few pulls to suck the new gas into the lawn mower carburetor, so be prepared to clean and dry the plug a few more times.

Add fuel stabilizer when you fill up the tank to help protect the gasoline in there from dirt and moisture.

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Check the Spark Plug

Start by making sure the lawn mower spark plug cable is connected to the plug itself. It’s quite possible that it got pulled off there over the winter while the mower was being stored in the garage.

If that’s not the issue, the next step is to remove the spark plug to see if it’s wet. There’s no way the engine will start if it is. So clean the plug with carburetor cleaner and let it dry. Cleaning it with compressed air isn’t enough; you need a solvent to remove oil residue. If it’s really grimy and dirty, it might be best to change the spark plug.

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Check for Debris in the Mower Deck

Grass clippings can get clogged in the mower deck, which can prevent the blade from turning. This is a common problem if you’ve cut wet grass or let the lawn get especially long and bushy between cuttings. If the cord is hard to pull, that’s a good sign that there’s debris clogging up your mower’s deck.

This is a pretty easy problem to solve. With the mower off, flip it on its side or upside down and scrape out the gummed up grass clippings. Once that’s done, you can flip it back over and start it up again.

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Check the Air Filter

The lawn mower’s carburetor regulates the mix of gasoline and air going into the engine where it’s burned to create power. Before air goes into the carburetor it passes through the air filter which prevents dirt and debris from getting into it.

If the air filer is clogged or dirty, it throws the ratio out of whack. Sometimes that results in your lawn mower smoking, and sometimes it prevents it from starting entirely. So take a look at the air filter to see if it’s dirty. If so, you can clean it or just change it outright.

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Check the Carburetor

Another common reason for a lawn mower that won’t start is a clogged or dirty carburetor. It can also cause your mower to run rough or spew black smoke when you’re trying to cut the grass. If that’s the case, you may need to clean the carburetor.

To get to the carburetor, you’ll have to remove the air filter. Once that’s out of the way, you can remove the carburetor in order to clean it.

Once it’s out, check for corrosion. If you see chalky/powdery white corrosion like this, it’s probably better just to replace it. To clean it, take it apart and spray carburetor cleaner on the parts and inside the housing. After that, put the carburetor back together and reinstall it in the mower.

Check the Fuel Filter

Like the air filter, the fuel filter prevents dirt and debris from getting into the combustion chamber of your lawn mower’s engine, taking that stuff out before the gas gets mixed with air in the carburetor. Problems with the fuel filter might also result in the engine sputtering or rough idling, even before it gets to the point of preventing the mower from starting.

Fix Your Mower. Only Runs With Choke On

To start, tap the side of the carburetor to help the flow of gas. If that doesn’t work, you might have a clogged filter.

Not all lawn mowers have a fuel filter, but for the ones that do, it’s usually located in the fuel line or the fuel tank. To find out where the fuel filter is at, check your lawn mower’s owners manual, which will also tell you what type of filter it is.

If the filter is in the fuel tank, you’ll need to drain the gas from the mower into a drain pan, assuming you can’t run the engine until it’s out of gas. If the filter is in the fuel line, clamp off the fuel line before removing the filter. Once you have the filter off, you can check to see if it’s dirty and clogged by holding it up the light. If it is, install a new one. Make sure it works with this lawn mower maintenance checklist.

How Do I Fix Kohler Engine Surging?

Surging on small engines such as a Kohler engine can cause by a lean condition, as any leanness is likely caused by an exposed vacuum leak. These machines’ RPMs can go surge up and down, and at full throttle, or pop through the muffler. And, if the fuel supply is clean as well as good flow it comes down to carb service.

Now, how do I fix Kohler engine surging then? Try cleaning the old carb or replacing the carburetor to resolve a Kohler engine surging. You should also troubleshoot and check the electrical circuits, or the jet.

Reasons behind the surging

Investigating the root of the problem is the first thing to do before looking for a fix for surging issues. Some of the reasons might be:

Lean condition (which is the occurrence of leanness is a new carb owing to vacuum leakage)

Insufficient amount of fuel consumption

Using lower-grade fuel on the engine

Inputting inappropriate type of fuel on an engine specifically designed to perform on another.

Contamination of water with fuel due to heavy rainfall.

Stored below optimum temperature

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Worn out or periodically skipping gears.

How Do I Fix Kohler Engine Surging?

A healthy engine will provide you with more power out of the engine. There are several methods to follow to stop your Kohler Engine from surging. Try following steps.

Kohler Carburetor Troubleshooting

  • For the carburetors having the Plastic Slow Idle Speed Jet, the solution is quite simple, that is, remove the plastic jet, and use a drill bit to bore the hole out to a larger diameter.
  • Maintain the saying: “Start low and go slow”- which expresses don’t pick a large drill bit and bore your jet to too big of a hole. If you overdo it, you’ll waste too much fuel. Keep in mind, you can always go larger but you can’t go smaller without buying another plastic jet.
  • There are black and red jets. Although the black jets are smaller than the red ones, the red ones still aren’t big enough.
  • On the contrary, the carburetors having non-adjustable jets won’t work the same. In this case, a low idle adjustment needle comes to the rescue. An initial check-up of the fuel line, the fuel filter, and the air filter can give you an idea if they’re clogged or not. If yes, then clean them with a careful hand.
  • If not, then the problem might be lying in the jets. There’s a needle right underneath the fuel cap to monitor the fuel flow. Turn the cap counterclockwise a little bit and run the engine again to see the difference in the noise. Continue to turn the cap with a screwdriver until the sound becomes better.

Examining Electrical Circuits of Engine

Check the connection from the battery to the ignition switch to see if contact is present. Once secured, follow the circuit through the safety switches to the starter solenoid to troubleshoot the readings of both voltage and continuity.

With the aid of proper reference material at hand, you can easily evaluate if the electric circuit is in good shape or not. So, in this regard, you need a volt-ohm meter to check the flow.

Replacement of Carburetor

If cleaning the old carb doesn’t create any impact (as there’s water, soil or any other contaminants might be present), then buying a new one will be a feasible solution.

Make Governor Adjustments

Try making made adjustments to the governor as instructed in the Kohler service manual, and change the spring setting, if the governor is the issue.

Precautions to Avoid Surging

You can easily keep your Kohler engine in a sound shape if you consider maintaining a few things. Such as, refrain from using fuels that are not suitable for your engine. Store your machine at an optimum temperature to increase its vital.

Also, check your carburetor regularly and release if any amount of extra air pressure is observed inside. As a result, the engine will dodge lean conditions pretty smoothly. Look for cables and plugs to ensure a proper connection before starting the engine.

FAQ

Can spark plugs cause surging?

Ans: Dirty or worn-out plug can cause vehicles surging which ends up in jerking acceleration ultimately. Sparking plugs might not create ignition to the fuel in your engine to initiate a good speed. As a result, bumpy motion occurs.

Can a bad fuel filter cause surging?

Ans: Yes, by decreasing air pressure clogged fuel filters. Fuel filter requires being clean to have enough flow of fuel spontaneously.

How do I know if my carburetor is too rich or lean?

Ans: Poor fuel economy, slow acceleration, the intense smell of gasoline at standby condition, uneven pace (will often slow from regular idle RPMs and then stop), cold starts don’t demand choke, black spark plugs or black muffler end pipes- these are the common signs to look for.

Why does my Kohler engine keep shutting off?

Ans: It’s probably because the carburetor might be jammed from leaving traces of gasoline every now and then. Clean it cautiously to see the improvement.

To Conclude

Kohler engine is a multifunctional appliance and systematic use is needed to keep surging at arm’s length. over, constant monitoring of carburetor, fuel movement, pressure, and electrical wires will save you from the hassle of repairing your machine. However, if your Kohler engine still has surging issues, you can try out the steps described above or seek professional help.

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Lawn Mower Starts Then Dies – Here’s the Fix!

Is your lawn mower starting up just fine and then quitting? When your lawn mower starts then dies, it not only delays the completion of your lawn care chores—it can also be kind of embarrassing. Imagine your neighbors glancing over curiously, wondering what on earth is up with you and your problematic mower.

Worse still, a lawn mower is a complicated machine, so at first glance, you might not have any idea how on earth to solve the problem. You might be tempted to just write the whole thing off and buy a new one. However, you shouldn’t throw in the towel yet, because there are a number of possible causes for why a lawn mower starts then dies—and you can actually resolve some of them fairly easily, giving you plenty more mowing sessions with that lawn care machine.

Determine the Fuel Status

First—and this may seem like a no-brainer, but bear with us—check the fuel levels. You may have been absolutely certain that the mower still had gas in it the last time you started it up, but perhaps someone else has run the mower since then, or maybe there just wasn’t as much fuel in the tank as you thought.

Whether you’ve got a Briggs and Stratton lawn mower, a Toro lawn mower, or some other type of gas mower, checking the fuel should be fairly simple. Some lawn mowers have an actual fuel gauge, while others do not. For those that don’t, you can take a quick peek inside the tank. You should also check the fuel line for clogs and take a look into the carburetor bowl to ensure that fuel is reaching that part of the engine.

If there appears to be enough fuel, and it’s flowing through the fuel line, you would move on to other potential sources of the problem. However, if your fuel is low or it looks thick and sludgy, your first step is to drain off the old fuel (being mindful of local regulations for disposal of such waste products) and add fresh fuel. You may find that a gas refill or replacement solves the problem.

Gasoline can go “stale” and start to “varnish” or sour within just two or three weeks of being left idle, so it’s a good idea to drain it off whenever you plan to stop using your mower for a while.

Check for a Clogged Carburetor

Has it been a while since you last started up your lawn mower? Maybe it’s been sitting in the garage or in a shed for a while, unused, while you were on vacation or over the cold winter months. That period of disuse can be one reason for the lawn mower’s malfunction.

As time passes and the mower sits idle, some of the more watery components within the fuel can evaporate. That means the rest of the fuel congeals into a sticky, thick mess. When you finally start up the lawn mower again, that thick, gooey fuel does not flow through the engine properly or burn as it should. Instead, it clogs up the carburetor. So the engine starts, but then it stalls.

It is not possible to thoroughly clean a carburetor without removing it. But still, if you want to try, you can skip to the next part.

Removing the Carburetor to Clean It

If the problem with your lawn mower is the carburetor, you may need to take it out of the machine in order to clean it. The location of the carburetor can vary depending on the type of lawn mower. However, it is typically attached to the engine’s side or top. It is also generally located below or behind the air filter and linked to the gas tank.

Before you start, you’ll want to gather the following tools:

When you’re working over the carburetor, be sure to follow proper safety protocols by wearing gloves and safety glasses.

Step #1

Remove the air filter cover and filter.

Step #2

Remove the air filter housing.

Step #3

Remove the fuel hose from the carburetor and then take off the screws, nuts and clamps holding the carburetor in place.

Step #4

Remove the fuel linkage. Carefully rotate and pull the carburetor until you are able to get it free.

Step #5

Now you’ve got a detached carburetor. You’ll need to remove the screws and pin that secure the float valve; take it easy on them since they could become stripped. The gasket can also be fragile, so you should be careful while working with it.

At this point, some carburetors will have splash plates you need to disconnect and set aside. Take off any other screws, gaskets, O-rings, or hardware remaining on the unit, including the choke if it is removable.

If it is a Quantum mower, typically there are three parts that you will want to replace:

Step #6

Now you’ll need a can of carburetor cleaner or a can of Coke. Coca-Cola is great at removing rust because of its citric acid. You can pour it into a basin and soak the carburetor and its components in the Coke for a few hours. Before using any harsh chemicals, you should try this method first. You will be impressed with the result!

Then you should scrub with a brush. Some compressed air is also helpful for blowing gunk out of hard-to-clean areas.

Step #7

An important part to mention is main jet. It is the most common reason a lawn mower starts and then dies. That is why you should carefully clean it. Poke a bread tie wire through the small hole of the main jet and clean it up. Also, you need to be careful not to overtighten this bolt.

Step #8

It’s worth double-checking to make sure the hose doesn’t have any leaks or cracks. If you do find damage or wear, it’s important to replace that fuel line. You’ll also need to clear out and replace the old fuel within the machine’s tank before you start up the mower again.

After you’ve thoroughly cleaned the carburetor, put it back together as it was. If you don’t have instructions for the lawn mower, be sure to take photos throughout the disassembly process, so you know exactly how everything is supposed to fit back on.

Using Spray Cleaner for the Carburetor

You could also try a spray version of the cleaner. If you’re hoping to resolve the problem without removing the entire carburetor, you can try the carburetor aerosol spray cleaner with the carburetor still installed.

Before you start cleaning, be sure that the lawn mower’s engine has cooled down. Once that’s done, take off the machine’s air filter cover and the filter itself, along with the external cover of the carburetor. Leave these parts aside and wait until the carburetor’s parts have all dried out thoroughly.

Now that the carburetor is dry, start up the engine again. You’ll be able to see the moving parts inside the carburetor. Be very careful as you place the spray tip of the cleaner can into the carburetor and begin to spray. The natural movement of the carburetor as it’s running should help to carry the cleaner throughout. Keep spraying until you feel that you’ve added enough cleaner.

Turn off the engine again and then find the choke shaft of the carburetor. Spray some extra cleaner there. If, at any point, the instructions on the spray cleaner contradict these steps, follow the manufacturer’s recommendations for use.

Once you’ve completed the cleaning steps, put the exterior cover of the carburetor back on, and reattach the air filter and its cover. You may need to swap out the air filter for a new one if it looks dirty or damaged. Before you try running the engine again, make sure that you’ve drained the old fuel and introduced fresh fuel into the tank.

Identifying Carburetor Corrosion

There’s one other thing that might be wrong with the carburetor besides a clogging issue. When you check the carburetor, do you notice a powdery or chalky residue all through the inside? That white corrosion is a very bad sign. In fact, it usually means that you will need to replace the carburetor entirely.

Some users suggest that you may be able to revive the carburetor for cases of mild corrosion by boiling it in vinegar for about 30 minutes to cleanse the corrosion. There will still be pitting and damage afterward, but if the damage isn’t too extensive and the corrosion hasn’t progressed too far, you may still be able to reinstall the unit and continue to use it without having to purchase a replacement.

Test the Fuel Cap

As the fuel level within the lawn mower’s tank drops naturally during use, the air is allowed to seep into the tank through a tiny vent in the fuel cap. The inflow of air into the tank is important to prevent a vacuum from forming inside the tank since that could hamper its correct function. This type of vacuum is known as a vapor lock.

If the fuel cap vent becomes clogged or blocked, air can’t get into the tank and the vapor lock forms. So when you try to run your gas mower, it starts and then shuts down.

It’s easy to test whether or not the fuel cap is at fault. Just loosen it a bit to allow a small amount of air to seep in. Then restart the engine again and see if it keeps running. If the lawn mower continues to function well as long as the cap is loosened, the problem is a blocked or damaged vent in the fuel cap. All you need to do is replace the fuel cap, and your mower should start functioning properly again without any more issues.

Replace the Spark Plug

If your lawn mower starts then dies right away, another possible culprit for the issue is the spark plug. A spark plug problem will result in the mower being more difficult to get going, and in some cases, the faulty spark plug may prevent it from starting at all. Signs of spark plug issues include the following:

  • A stuttering motor
  • The mower requiring multiple cords pulls to get going
  • The repeated key turns to start
  • Engine function cutting out unexpectedly
  • Power loss requiring a restart
  • Slow acceleration
  • Excessive consumption of fuel by the mower
  • A strong smell of burning fuel

If you’re noticing any of these signs, in addition to the mower being hard to start, the spark plug is likely the culprit. The spark plug enables that initial ignition spark that lights the fuel and gets the engine going.

How Often to Replace a Spark Plug

Some lawn care experts recommend changing a lawn mower’s spark plug once a year, or once per season, or once per 25 hours of use. You can push these boundaries a bit in order to get more use out of each new spark plug and cut down on replacement costs, but you definitely need to keep a close eye on how well your mower is functioning as you near that season’s end mark, or as you get closer to a full 25 hours of use.

Cleaning the Spark Plug

Sometimes, all you need to do is clean the spark plug. Maybe it has simply gotten gunk on it from regular use, and it’s too wet to do its job of sparking and igniting the fuel. Check it for gas or oil buildup before you buy a replacement.

Take a careful look at the plug’s center electrode, which is the bit that yields the spark. Its tip should be a flat, even surface. If you notice that it is more round than flat, or if it looks worn down or corroded, you need a replacement.

Lawnmower Revs Up And Down Fix

However, if the structure of the center electrode is intact and the plug simply looks messy or dark and oily, try cleaning it up. You can clean a spark plug with a little bit of starter fluid or brake cleaner. Let it soak in that fluid for 10-15 minutes, and then use a rag to wipe off any excess and polish it up.

Check it again for corrosion or wear and tear before putting the plug back into the mower. You can also take a look at the spark plug threads to ensure that they look clean and undamaged.

Replacing the Spark Plug

If your spark plug is beyond repair, take a photo of it or take the actual device along with you to your local hardware store or tool supply shop, so you can be sure you’re getting an exact replacement.

The same principle applies if you’re ordering a new plug online; you must be sure that the replacement spark plug is precisely the same as the original. The wrong kind of spark plug can actually damage your lawn mower’s engine, necessitating a serious and costly repair or possibly forcing you to replace the entire unit, so make sure you get it right.

When you’re replacing the spark plug, be sure you clean the entire area where it connects so the new plug is seated correctly. If you have trouble removing the old plug, use some lubricant and let it rest for about 10 minutes, then take out the old worn plug with a wrench or a socket driver.

Double-check the electrode behind the plug to make sure it doesn’t look too damp or corroded since those signs could indicate an engine choke problem or a carburetor issue, respectively. When you place the new spark plug into the correct spot, be careful not to overtighten it. You just want it to fit snugly before you reattach the spark plug wire.

Causes of Spark Plug Failure

It’s worth noting that you should also think about the reason behind the spark plug’s failure. Why did your mower’s spark plug fail in the first place? Was it just because of regular wear and tear and use, or could there have been another reason?

Sometimes these spark plugs can become worn or damaged due to other problems with the mower’s engine. If that’s the case, and you replace the plug without identifying the root cause of the damage, your new spark plug is likely to suffer the same fate.

Think about possible root causes of the spark plug failure, such as a dirty air filter, a faulty or filthy fuel injector, damage to the distributor case, or some problem with the mixture of fuel and air within the gas mower tank.

Check all of these potential issues to ensure that your mower is in good shape. Just like your car, the mower needs an occasional tune-up, and this is as good a time as any to make that happen.

Final Thoughts

If you don’t want to go through the entire process of troubleshooting the problem, cleaning the carburetor, or enacting any of the other fixes or repairs, you don’t have to do any of it.

You could take the lawn mower to a repair and maintenance shop and have the experts take a look. They can identify why the lawn mower starts but then dies and then fix the issue for a fee. However, before you visit a lawn mower repair shop, be sure to check online and ensure that they have good ratings and reviews and that they are known for being fair and honest with their customers and not overcharging for unnecessary services.

Josh Hurd has been freelance writing since 2006. He attended the University of Akron, graduating with a Master of Fine Arts in creative writing.

Why Does My Lawnmower Backfire? How can I fix it?

After working smoothly for some time, your mower starts backfiring unexpectedly. Engine backfire can quickly leave the owner or operator in distress because a backfire can be loud and frightening. A backfire is just like a small explosion, it is not dangerous most of the time, but the causes behind a backfire could be hazardous for your engine. If your mower’s engine backfires and you understand why it does so, you can fix the problem and make sure it does not do it again so you can keep using your mower like normal. Backfires happen unexpectedly and mostly catch you off guard while turning off or starting your engine, so it is beneficial to have at least the basic info about engine backfires and how to deal with them.

Why Does My Lawnmower Backfire, and how can I fix it:

Backfires occur when fuel comes close to a spark outside the engine combustion chamber and is either fuel-related or engine-related. Sometimes, fuel can escape your engine’s cylinder before the valves close or during the exhaust stroke and enter the engine or exhaust. If a sufficient amount of unspent fuel manages to enter the engine and comes close to the spark, it will ignite, causing a small engine explosion. Combustions of fuel anywhere in the engine other than the combustion chambers or in the exhaust will always produce a bang or backfire.

Engine backfires are caused by basic and simple chemical malfunctions, and solving the backfiring problem is not difficult. It is necessary to fix the issue as soon as possible so that the engine and exhaust are not damaged beyond repair. Information about engine backfiring in lawnmowers presented in this article will surely help you manage a backfiring situation in a better way.

What is the cause of a Lawn Mower Backfire?

Generally, a lawnmower backfires because the fuel mix being too lean. This means there is more air in the gas mix, and it results in incomplete combustion. The gas that is pushed to the exhaust will still contain gas. When it reaches the exhaust, this gas will exnight spontaneously and makes a bang sound. This is the backfire.

Backfiring in a lawnmower and other Small Engines:

Lawnmower engines are regarded as “small” internal combustion engines. Power is produced in internal combustion engines by the combustion of an air-fuel mixture in the engine’s combustion chamber. This production of power takes place in either 2 strokes or 4 strokes. In both cases, combustion of the air-fuel mixture is the most vital stroke in which a spark ignites the mixture, causing an explosion and, therefore, a release of energy. Combustion of fuel takes place in a controlled manner inside the combustion chamber. Combustion or burning of fuel anywhere else will cause a bang, which is called backfire.

Backfiring in lawnmower engines can be caused by either fuel-related causes or engine-related causes. Both are explained below.

Fuel-Related Issues:

Gas in the engine’s combustion chamber requires a certain amount of air to burn properly. Just like any burning, gas combustion requires oxygen. Each engine is designed so that the correct air-fuel mixture is provided to the combustion chamber during operation. All strokes are timed perfectly for the complete combustion of fuel, maximum energy release, and smooth machine operation. If the air-fuel mixture is in an incorrect proportion, it will cause all sorts of problems for the engine. For example, if the fuel is too rich, it could result in your engine blowing smoke.

The timing of all processes in the combustion chamber is vital. A process happening early or getting delayed even by some seconds can cause problems. An incorrectly proportioned air-fuel mixture can cause a timing disruption.

If there is too much air in the combustion chamber, the engine will not create a spark with enough power to ignite the fuel for some seconds. While the ignition is delayed, other combustion chamber processes keep happening in the way they are supposed to be. This causes the fuel to pool in the low spots along with the exhaust. This fuel can then get ignited outside the combustion chamber, producing an explosion that you know by the name backfire.

– Backfire Fix: Fuel related

An air-fuel mixture with more than the correct amount of air is known as low-pressure fuel. If your lawnmower is backfiring, it could be because low-pressure fuel is being pumped into its engine’s combustion chamber. Look for reasons for low-pressure fuel. Possible causes of low-pressure fuel include old fuel filters and failing fuel pumps.

Replace the old fuel filters and get the fuel pump repaired. If low-pressure fuel were the cause behind your mower backfiring, these fixes would solve the problem.

Engine Related Issues:

As mentioned above, the timing of all engine processes is very crucial for its smooth function. Engine-related issues that mess with the timing can cause backfire.

If your lawnmower is backfiring, check for its motor’s timing. If the motor timing is not right, the engine may ignite the fuel while the intake valves are still open. This can cause a backfire in the engine.

After prolonged use, the timing between the engine and the valve can become disrupted or out of the correct setting. This situation inside the engine results in backfires.

– Backfire Fix: Engine related

To solve the engine-related causes of backfires, take care of the following things.

  • Engine Tune-up: An engine tune-up will restore the engine and the valves to the correct timing settings. Both valves will then open and close at the right time preventing the fuel from getting burned in the engine.
  • Spark Plug: Clean or replace the spark plug. Clean the plug’s wires and the plug chamber. Doing this will ensure that the ignition occurs at the right time and will prevent the backfires that result from mistimed ignitions.
  • Fuel Filter: Keep your mower’s fuel filter clean and replace it with a new one every year. Consult your mower’s user manual for more info in this regard.

Moving forward from the kind of issues that could cause engine backfires, let’s get into the details of when the engine backfires and what significance does the backfiring time hold.

During Starting:

Lawnmowers aren’t supposed to backfire when you are starting them. If your lawnmower backfires when you try to start it, it indicates that the mower is damaged somehow.

Many mowers have parts that serve to safeguard other more expensive parts. These inexpensive parts, such as the flywheel, sacrifice themselves to protect the expensive parts such as the crankshaft. If, during mowing, your mower runs over a large rock or its blades hit an obstruction, the flywheel breaks and won’t engage when starting again. This will cause your engine to stutter or backfire as you try to start it.

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A mower with a broken flywheel won’t start normally, so it can’t be used until the flywheel is repaired. If your mower backfires when you try to start it, the indication is of damage. In this case, you must take your mower to a professional for repair.

During Shut-off:

Sometimes, when you mow, and you turn the engine off, or when your mower is idling, it will backfire. This is most probably happening because you are slowing your engine too fast.

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

To reduce this kind of backfire, make sure that you gradually reduce speed and let the motor idle for 10 to 15 minutes before turning off the engine.

Another potential problem that could be the reason behind your mower backfiring when you try to shut it off is engine overheating. Engine overheating can be reduced by increasing airflow to the engine. If your mower backfires during shut-off and you suspect it could be because of engine overheating, take your mower to a professional or contact the manufacturer to learn ways of increasing airflow to the engine.

After Shut-off:

Sometimes, your mower backfires right after the engine is turned off. Backfiring that occurs after shut-off is caused by problems with the carburetor or muffler.

Get your carburetor checked for incorrect settings and your muffler for wrong construction. Getting these two components adjusted will solve the backfiring after the shut-off issue.

Using the wrong kind of gasoline can also cause after shut-off backfires. Gasoline that has alcohol ignites differently than gas that does not have alcohol. Gas with alcohol can get ignited in the muffler resulting in a backfire. Switching to gas with lower alcohol content or alcohol-less gas could solve the mower’s problem of backfiring after shut-off.

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Does a backfire damage a lawnmower engine?

Generally, a backfire does not damage a lawnmower or another small engine machine. The explosion you hear is in the exhaust, and not in the engine. But when your lawnmower experiences a lot of backfires, it can damage the exhaust and engine over time. I always recommend fixing the backfire issue.

A lawnmower exhaust is not designed for backfire explosions, and the additional heat and strain can damage it over time. Depending on the reason for the backfire, also the engine can experience additional wear and tear. Resulting in a shorter life, and potentially engine failures.

Anti-backfire Equipment:

Special parts can be installed in some mowers to prevent them from backfiring after shut-off. Such features are called anti-after-fire solenoids. Installing them will let you turn off the mower’s engine at any speed without causing fuel to shoot to the muffler.

Installing anti-after-fire solenoids requires professional help. Take professional service if you want to equip your mower with such equipment.

Final Remarks:

Engine backfires sound dangerous, especially when they catch you off guard, almost every time there is a backfire. An explosion in the mower sounds crazy, but it is not something to worry too much about. The causes of engine backfires are mentioned in this article. Using this info, you can determine why your mower is backfiring and look for possible fixes. So, the next time your mower backfires, put the acquired knowledge to use and get the issue fixed before it causes permanent damage to your mower.

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