Lawn Mower Sputtering? Here’s How to Fix It
Lawnmower maintenance is a crucial part of keeping your mower running properly. Regular maintenance promotes the overall health of your lawnmower and its ability to properly operate. But even with regular maintenance, there may be times when you experience issues with your mower. One common problem among lawnmowers is sputtering. Lawn mower sputtering is generally an inexpensive and easy fix that can be done on your own as part of your regular maintenance.
In this article I’ll share what causes a sputtering lawn mower, and what you can do to fix this common problem.
About Lawn Mower Engines
The engine of your mower relies on the right combination of fuel, air, and a spark (for combustion). Your mower needs each of these to prevent the mower from sputtering and eventually dying.
For the most part, many of the issues that cause a sputtering mower can be fixed by the weekend warrior.
However, there are times when it is best to use a professional for the job.
You’ll want to check a few items to determine what’s causing your mower to sputter, and that will determine if it’s a DIY fix, or you need to call in a professional.
Let’s look at some reasons why your lawnmower may be sputtering and how you should address each of these issues.
Identifying the Cause of a Sputtering Lawn Mower
Below are some of the more common reasons for sputtering lawnmowers and how they can be resolved.
Old Fuel or the Wrong Fuel
The gas you get at the local gas station will generally contain about 10% ethanol. It’s cheaper than pure gasoline, and works fine for cars, but I don’t use it in my mower because it’s low quality.
Ethanol burns quickly and can potentially melt plastic parts, leading to sputtering in your mower. And if you use ethanol blended gas, only buy a little at a time.
If it sits in your garage for more than a couple of months it will go bad and can lead to a sputtering mower.
You can use a fuel stabilizer to extend the life of the gasoline, but I recommend using an ethanol-free gas. It’ll burn cleaner and help your mower to start on the first pull and roar like a tiger.
I use 4-cycle Tru-Fuel in my Honda mower, and love it. It’s pricey, but I highly recommend you try it. You can buy it locally at most box stores, or you can order it online (Amazon link).
Clogged or Dirty Air Filters
Dirty air filters are one of the most common reasons lawn mowers sputter.
Dirt can be present in the apertures that lead from the carburetor and the fuel filter and interrupt the flow of fuel supply to the combustion chamber.
You want to be sure to clean or replace dirty air filters.
Paper air filters will need to be replaced. But you can generally clean foam air filters with a drop of liquid dish soap and warm water.
After cleaning the air filter, squeeze dry and air dry.
My Honda mower uses a paper air filter which I replace every year as part of my spring mower tune-up.
During the summer, I remove it and blow the dust and debris off before each mow.
Dirty Fuel Filters
Any filter will get dirty with time, and just like the air filters, fuel filters in a lawn mower need to be clean.
Replace yours if they’re dirty.
Clogged fuel filters prevent the flow of gasoline to the engine which can lead to a lack of fuel needed for proper functioning.
This imbalance of air and fuel in your engine can cause your mower to sputter and run rough.
A Bad Gas Cap
Misfires can occur with an improperly vented gas cap on your mower.
If your gas cap has improper venting, too much air can be allowed to enter the gas tank (or too little). This can cause a vapor lock.
It’s an easy fix – just replace the cap if it is damaged or bent or if you see that the vent hole is restricted.
That Carburetor is FILTHY
Gunky deposits can occur in the apertures and carburetor.
This buildup is from the sticky by-products of hydrocarbon and combustion.
Using a carburetor cleaner spray (this one on Amazon is what I use and swear by) on a regular basis can loosen dirt deposits and keep your mower’s apertures and hoses clean.
I give my carb a shot every time I clean my air filter before I mow.
Water in the Fuel Tank or Fuel Line
Water prevents the mower cylinder from properly igniting. Remove the cap and check the gas tank for evidence of water (if you see the liquid separating or looking like two different colors).
If there is water in your tank, siphon or drain it, then add new gas.
After old gas in the line works its way through the mower’s engine it should stop sputtering and run like new again.
Check the Spark Plug
Worn or damaged spark plugs make the engine difficult to start. If the plug is damaged, worn, or deteriorating you should replace the plug.
If the tip is fouled or dirty, just clean it with a wire brush and reset to the mowers manufacture’s settings.
You can also look into purchasing another brand of spark plug to see if the mower runs better with a different brand. The plug that comes from the factory with some mowers doesn’t work great on some lawn mower brands.
The spark plug is generally not the first thing I’ll check for a sputtering mower. But a dirty or damaged plug can sometimes be the cause.
Your spark plug is an easy item to replace, and costs about 8 at your local hardware store.
I replace my plug every other year as part of my annual maintenance routine. If it has been more than two years since you’ve bought a new plug, I recommend replacing it as part of your tune-up to fix your sputtering lawn mower.
Your Carburetor Has Issues
Some carb cleaning spray will help if your carburetor is simply dirty, but sometimes there are other issues that can cause lawn mower sputtering.
The carburetor affects how well the mower runs. The wrong blend of air and fuel can cause the carburetor to run rough.
The carburetor must have the right amount of air and fuel to run correctly, and while the average weekend warrior can probably find and remove his mower’s carb, due to its complexity, the carburetor can be tricky to clean or repair.
If you’ve tried everything else on this list, it’s likely a carburetor issue and your mower may require professional service.
A professional can determine the repairs, cleaning, and replacements needed. They’ll then get the carburetor working properly.
First, check to see if your mower is covered by a warranty of any kind. If it’s not, find a local small engine repair guy (or gal), and have your mower serviced.
It’ll be cheaper than you expect.
A Dirty Mower Deck
Caked grass on the mowing deck can cause the mower to sputter.
If you have tall or wet grass you may have noticed that your mower started sputtering as you mowed your lawn.
Check the underside of the mower for excess grass caked on.
Use a wrench to remove the spark plug to prevent the mower from turning on while you work. Then scrape the excess grass using a scraping tool such as a paint scraper.
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by Sarah The Lawn Chick
Sarah’s blog, Lawn Chick, is read by over 2 million homeowners each year and she is regularly cited as an expert source of lawn care knowledge by major publications. Her goal is to meet you where you are, and help you achieve a yard you’ll be proud of. Ready to take the next step toward improving your lawn? Grab her free lawn care cheat-sheet: What to Do When. Take the Guesswork Out of Lawn Care, or upgrade your garage by browsing her favorite DIY lawn care products.
Top Reasons Lawn Mower Runs Rough — Lawn Mower Troubleshooting
thoughts on “ Lawn Mower Sputtering? Here’s How to Fix It ”
I am a 62 year old female just having to learn how to care for my own mowers, riding push. Your article was more informative than the many others I’ve read! Thought it was sputtering due to the spark plug but now I’m sure it’s the carburator. FYI, when my husband was the main mower man both mowers spent more time in the shop than on the lawn and the cost of repairs would have bought me a brand new one. If it didn’t start immediately off it went to the shop. It never cost less than 100, usually more plus 60 for a 1 mile pick up. I really think the repair man had my husband pegged for a sucker and that may be accurate. That’s the main reason I decided to care for them myself. Since I became the main mower lady and actually read articles like yours it’s smooth riding! Lol Thank you so much for your help.
Thanks, Teresa! Your article made my day – I’m so glad you found this helpful and are tackling these projects yourself!
My Lawn tractor Craftsman R1500 30″ deck, Mod.#247.29900 by MTD, sputters (like running out off gas) after 20-25 minutes of operation and eventually dying. After cooling off for 30 minutes or so, it starts and run again. It is frustrating! Can you please help my with my problem? I installed new fuel filter, put new gas. (I run out gas as season changes). What else can I check to make it work? Thank you in advance Mick T.
Hey, Mick – It sounds like you may have a clogged gas cap vent. The gas cap on most lawn tractors has a small hole in it which allows air to get into the tank. This is important because as your mower burns fuel, that empty space in the tank needs to be replaced with air for the correct mixture of fuel in the engine. If air can’t enter the tank as your mower burns the fuel backward pressure is created and your engine will struggle to get enough gas, which is why you may hear your engine surging or sputtering the same way it would if it was running out of fuel. Typically when I hear that the mower works well at first, then this issue happens after 20 minutes or so, this is the culprit, because that’s when you’ve used enough of the fuel for the pressure imbalance to become an issue. A good way to trouble-shoot and determine if this is definitely the issue is to run the mower, and when this happens and your mower won’t start, open up the gas cap and then put it back on. This will relieve the pressure, allow air in the tank, and get things back in balance. If the mower starts up right afterward and runs fine, you’ve identified the problem. Clearing the vent is easy – just find something small enough to slide through the vent hole and clear out any dirt or debris that’s in there, and you’re good to go. If it’s cold where you are, you may need to bring the cap inside to warm it up first as the solids in there may be frozen, making them tougher to remove. Hope this solves your problem!
Great help. My lawnmower was starting and sputtering and dying in a couple of seconds. Tried NEW GAS (the one in the tank was a year or more old) and it WORKED.
Lawn Mower Troubleshooting: 4 Things to Check before Calling the Repairman
Jennifer is a full-time homesteader who started her journey in the foothills of North Carolina in 2010. Currently, she spends her days gardening, caring for her orchard and vineyard, raising chickens, ducks, goats, and bees. Jennifer is an avid canner who provides almost all food for her family needs. She enjoys working on DIY remodeling projects to bring beauty to her homestead in her spare times.
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If you own a lawn mower long enough, you’re going to have to figure out how to fix it at some point or another.
There are some common problems with lawn mowers that you can assess and possibly fix yourself, before taking the costly step of getting a lawn mower repair service.
I’ll tell you upfront, I’m not a lawn mower mechanic and take no responsibility for your experience. However, on my homestead, we have had to learn to problem solve ourselves.
If you’re interested in checking into a few theories as to why your lawn mower could be giving you fits, here are a few things I’ve learned by trial and error over the years doing our own lawn mower repair:
The Lawn Mower’s Engine
A lawn mower engine has many parts, and each part could be the potential cause as to why your lawn mower isn’t working properly. Here’s how I go about checking into each part of our lawn mower engine:
Disconnect the Spark Plugs
Safety is first in my book no matter what I’m working on. When you’re dealing with any kind of engine, it should be disengaged before you begin working on it.
Make sure you disconnect the spark plugs because the engine can’t crank without them being in place. Remember to wear your protective goggles and gloves too.
Check the Spark Plugs
Spark plugs are a small component of the engine yet; they can cause big problems if they aren’t functioning correctly.
Therefore, check the condition of each of the spark plugs. They should be slightly brown and show some wear from use.
However, if they look corroded, melted, etc. they should be replaced. It’s also a good idea to do further research as to the condition of the spark plugs.
If they’re damaged, there’s a reason. By checking into the condition of the plugs, it could show you if there’s an underlying condition.
Through research, you should also be able to figure out how to fix the condition which is damaging your spark plugs.
Some conditions could be as simple as the oil not being changed frequently enough. Regardless, checking on the spark plugs, their shape, and why the spark plugs would be damaged, could help save further expense on your lawn mower.
Check the Ignition System
Lawn mowers have different ignition systems. As a general overview, check all the wires in the ignition system to make sure they’re all intact and clean.
If you notice a problem, research what type of ignition system your lawn mower has. You should be able to locate a diagram of the system through research.
Once the diagram is located, it will give you an idea of how the system should look, what parts might be in need of repair, and should point out any other issues you may have going on with your ignition system.
Carburetor Care
Carburetors can hold power in many mechanical situations. I’ve learned a great deal about carburetors when helping my husband fix up an old boat. If the carburetor isn’t cleaned and well-maintained, you’re going to have issues with the equipment running efficiently.
To begin, remove the carburetor and check each part. In my experience, the carburetor has tiny holes throughout it.
When the holes become clogged, your lawn mower can develop problems. It’s a good idea to start by cleaning each hole of the carburetor with a wire brush.
If you battle cleaning the holes, place the entire carburetor in lemon juice and let it soak for a while, then try cleaning it again.
When the carburetor is thoroughly cleaned, if it still isn’t functioning, check each part to make sure it’s functioning as it’s supposed to.
If it isn’t, replace the malfunctioned part of the carburetor and reapply the carburetor to the mower.
Fuel Lines Matter
If your fuel lines are having issues, again, your lawn mower will have issues. Problematic fuel lines affect whether the lawn mower get adequate amounts of fuel and it not.
When the lawn mower doesn’t get enough fuel, it won’t run. Some mowers have a hole in the gas cap. If this hole becomes clogged, the lawn mower won’t function properly.
Therefore, check the hole in your lawn mower cap to make sure it’s clean.
FIXED!! DOES YOUR LAWN MOWER SURGE AND BACKFIRE? ALREADY BEEN THROUGH THE CARB? THEN YOU MUST WATCH!
Next, check the filter on the gas tank. If it’s filled with gunk, use a wire brush to gently clean it.
From there, begin checking for holes in the gas lines. You can also run a long wire brush or a pipe cleaner through the lines to dislodge any blockages.
Intake Valve and Exhaust Valves
The intake valve’s job is to shoot the air-fuel mixture inside the combustion chamber. The exhaust valve’s job is to release the carbon monoxide and any leftover from the combustion.
These valves have a camshaft which moves them. The camshaft is driven at a specific rate by the engine. Obviously, these parts must work together in time, or your lawn mower will have a problem.
The valves can collect gunk which will stop the camshaft from moving as it should. Therefore, you should clean the valves and camshaft by hand or by using a cleaner.
If the valves are leaking, it’s most likely due to lack of oil changes. Change your oil and replace the valves if you notice this issue.
If the valves have become damaged, they’ll allow fuel to pass through at the wrong times. It will reduce the combustion within your mower. The valves should be replaced if you notice any damage to them.
Clean Spark Arrestor
This is a simple component of your lawn mower, and it sometimes goes overlooked. Its job is to catch any sparks your lawn mower may produce to prevent fires from happening.
By law, this piece is required on any outdoor equipment. The spark arrestor should be cleaned with a wire brush. By gently rubbing the brush over the part, it should remove any clogs.
Pistons and Gaskets
When trying to clean your lawn mower engine and locate potential issues, it’s easy to damage a gasket. If you’ve done everything listed above and things still aren’t running smoothly, try replacing the gaskets.
We also know pistons and their corresponding rings can have an impact on how your mower runs. Looking into this will require you to split your engine into two parts to access the pistons.
If you’re not an experienced mechanic, I wouldn’t recommend doing this step yourself because you can easily damage your lawn mower.
Don’t be afraid to take the lawn mower to a friend who is more experienced or a local repair person, if you’re under the impression the pistons could be a problem.
My Lawn Mower Won’t Start
If your lawn mower won’t start there could be a few potential issues. They’re easy enough to figure out:
Air Filter
If your air filter isn’t clean, it will make life hard for your mower. Before you become too flustered because the lawn mower won’t crank, take a quick peek at your air filter.
You can either use a brush to knock the dirt off the filter gently or if it’s beyond help, replace it.
A Dry Spark Plug
When I had a small push-mower, we had this issue many times. Check the spark plug to make sure it’s dry. It not, the lawn mower won’t fire.
Clean the spark plug with carburetor cleaner and allow it to dry before attempting to fire again.
Old Fuel
When you leave old fuel in your lawn mower, it can be hard on it. Fuel can be considered old if it’s been in your mower for a month or more.
If you have old fuel in the mower, siphon it and add fresh fuel. Be prepared to clean and dry the spark plug a few times because it may take a few tries to get the fresh fuel to the carburetor for the lawn mower to crank.
Check Fuel Filter and Lines
Your fuel filter and lines are another important part of the lawn mower and could hinder it from cranking.
Begin with a bowl and hold it under the fuel lines. Use a C-clamp to cut off fuel at each section as you work your way up the lines.
Start by checking the fuel filter. Remove any dirt or replace the filter if needed. As you work your way up the fuel line and move the clamp, hold the bowl beneath the lines.
With each section, there should be fuel flowing out. If there isn’t, you’ll know there’s a clog farther up and to keep working your way up the fuel lines.
When fuel begins to flow into the bowl, you’ll know you’ve found the clog, kink, or damaged part. Once fixed, you can put the pieces back together.
Carburetor
As mentioned above, the carburetor can be the answer to many issues when it comes to considering lawn mower repair.
If the lawn mower doesn’t crank, check the carburetor to see if it appears corroded. If it does, it’s time for a new carburetor.
If the carburetor looks fine at a glance, begin checking the different parts. When you locate a part which seems corroded, clogged, or damaged, replace the specific part of the carburetor.
Clogged Main Jet
The main jet could be another reason your lawn mower won’t crank. Clean it with carburetor cleaner. If the lawn mower still won’t fire, the engine is probably still not receiving fuel. In this instance, you’re most likely in need of a new carburetor.
It’s Running… But Not Well
Your lawn mower cranked. Happy day! Yet, it’s running choppy and unsmooth. You’re not sure how long it will continue to run in this condition.
It’s most likely still a wise decision to replace the carburetor. Sometimes it can be the difference between equipment barely running and running like a champ.
Help! My Lawn Mower is Blowing White Smoke
Your lawn mower is blowing smoke. What should you do?
The answer can range anywhere from ‘do nothing’ to ‘do a bunch.’ If your lawn mower is blowing black smoke, it’s burning more fuel than it is air.
If the lawn mower is blowing blue or white smoke, it means the mower is burning oil. Don’t panic because this could be a simple fix.
Lawn mowers are meant to work at certain angles. Let’s say you became carried away and ran over something which jolted your mower at a steeper angle than intended.
At this point, oil could’ve leaked. The lawn mower will burn the oil off, and life is good. If you notice the mower only blows smoke briefly, you’re probably in the clear.
However, let’s say the mower continuously blows smoke. This could be anything from the crankcase’s breather, a blown head gasket, or an old cylinder or rings.
Check all of these possibilities and again, you may need to call in a professional or someone more experienced to help.
My Lawn Mower is Sputtering
Yes, I’ve been here too. It’s frustrating when you go to mow, and suddenly the lawn mower sputters and spits at you.
There could be a variety of reasons for this happening too:
- Stale gas
- Dirty carburetor
- In need of an oil change
- A damaged spark plug
I’ve mentioned most of these problems above and how you can go about correcting them. Remember, if you have a damaged spark plug, research the condition of the spark plug to diagnose any underlying issues before replacing the spark plug.
After reading this overview, hopefully you know more about lawn mower repair. It should help you have a better idea of how to diagnose any issues before taking the expensive step of taking it in for repairs.
If you’re new to working on lawn mowers, don’t get frustrated with yourself. I’m not mechanically inclined, and it took me longer than my husband (who is mechanically inclined) to get the hang of each part.
With time, patience, and lots of research you should be able to diagnose and work out many of the issues which may arise when owning a lawn mower.
How to Winterize Your Lawn Mower
It’s important to look after any mechanical investment, and your lawn mower will need special protection over the winter since it will go unused.
Winterizing your lawn mower is not hard. Here’s all you need to know to take the best care of your lawn mower this winter:
Cover is Important
If you expect any piece of equipment to last, one of the most important steps you can take is to give it proper cover from the elements.
We all know winter can bring anything from cold temperatures, rain, ice, and snow. None of which is great for your lawn mower.
It can cause moisture build-up which invites corrosion and rust. Be sure to give your mower a proper cover, store it under a carport, or in a garage.
Iron Sharpens Iron
You guessed it. Before you put your mower up for the year, it’s time to perform basic maintenance on it. Basic maintenance could be anything from sharpening the blades, to oiling exposed moving parts on the mower.
If your mower has been having issues over the season, it’s a good idea to fix the problems before retiring it for the season too.
This will take one more thing off your busy spring to-do list. Before putting your lawn mower up for the season be sure you’ve made all necessary repairs, oiled everything down to make sure it won’t rust or worsen over the winter, and also sharpen your blades to make sure the lawn mower will be ready to use when spring rolls around again.
Time for an Oil Change
After running your mower all season, it’s a good idea to put fresh oil in it before putting it away.
Some people prefer to change it after a season’s use because they don’t want dirty oil sitting in the lawn mower all winter.
However, some prefer to do it at the start of spring to make sure there’s no moisture in the oil. The danger of changing the oil before winter is condensation could build up in the mower and add moisture to it.
However, if you top off the fluids in the lawn mower, theoretically, there shouldn’t be room for condensation to form. This is a personal decision you must make. Either way, be sure the lawn mower gets an oil change before use the next season.
Ditch the Fuel
Ditching the fuel is perhaps the item of greatest importance on the winterizing list. Be sure you drain the lawn mower of all fuel.
When you are positive you’ve removed it all, crank the lawn mower to let any remaining fuel which may have found a place to hide, burn off.
The issue with leaving fuel in your lawn mower is it becomes stale which isn’t good for your engine, but it also draws moisture to the mower.
Moisture is a problem because it can cause corrosion inside your mower. This damages parts and can create unnecessary expense.
Also, fuel can eat away at rubber and plastic parts in the fuel system. Again, this causes an unnecessary headache and expense.
Do yourself a favor and be sure to drain all the fuel from your mower before putting it away for the winter.
Unplug the Battery
Some people have shifted to all-electric mowers. Other people have traditional mowers with a battery. Either way, your battery needs care.
If you’re working with an all-electric mower, be sure to remove the battery over the winter and store it in a battery storage case. This case should protect it from the elements and keep the battery from draining.
If you’re using a traditional lawn mower, it’s still a good idea to either place a battery maintainer on the battery to keep it from draining or to remove the battery and store it in a safe location from the elements of winter.
Mr. Clean
One of my biggest pet peeves is when my husband tries to put something away knowing it isn’t ready for its next use.
Well, a lawn mower is no different. If your lawn mower is dirty, don’t put it away. You don’t want the dirt and grime to freeze to your lawn mower. It can’t be good for the paint job at the least.
Therefore, take the time to clean it well before storage. You should clean the mowing deck. Make sure all grass and debris are removed from under the mower.
Wet grass tends to stick to any place it can. Check the lawn mower to make sure it’s washed, dried, and all outdoor particles are removed.
Next, check the air filter. If it’s nasty beyond saving, toss it and replace it with a new one. If the air filter is dirty but can be cleaned, clean it.
Finally, as I mentioned above, take the time to oil any exposed movable parts of your lawn mower. If they’re starting to stick now, imagine what a few months of cold temperatures, damp weather, and sitting still will do.
Try to stay ahead of the game and anything which might need maintenance in the spring, go ahead and do it now.
Pay Attention to Where You Store
You may think if you store your lawn mower in a garage or carport, you’re good to go. Well, not exactly.
Accidents happen over winter. People rummage through garages and carports looking for items, they spill things, said items get all over everything, and many times the messes don’t get cleaned up because it’s cold and no one wants to freeze while cleaning it up.
In these instances, it matters where you park your lawn mower. Be sure you don’t leave cleaning supplies or fertilizers near your lawn mower.
If they get spilled on the lawn mower, they’ll cause corrosion. Again, this will hurt the lifespan of your mower.
Being careful to provide cover for your lawn mower and double checking what you park it next to can be the difference between a beautifully winterized lawn mower or a springtime headache.
We trust these tips will help you store your lawn mower in the best possible setting over the winter months.
Remember, the idea is to do what you can to prolong the life and health of your mower. An unhealthy mower will begin to give you problems. An uncared for lawn mower will eventually give out.
Lawn mowers are too expensive for them not to last. Do yourself and your wallet a favor by taking the time to properly winterize your lawn mower, as it is one of the biggest assets in caring for your yard.
My mower won’t start
Starting problems with your lawn mower fall into 2 basic causes: fuel problems and ignition problems. The following is a simple checklist you can follow to help isolate a possible cause. This is not an exhaustive guide and certainly not a repair manual. However, there a few steps you can take before taking it to the repair shop for a thorough fix.
Fuel
This is the first and most obvious thing to check, especially if you weren’t having startup problems last year. Be sure that the machine has an ample supply of fresh fuel. It’s amazing how often people will get their mower out of cold storage the first warm day in spring and find their mower just won’t start. Forgetting that they left the fuel in the tank from the previous year. Today’s fuels don’t age well. In fact today’s gasoline is much like milk and starts to go bad quickly, often in as short a period as 60 days.
Ignition
Make sure that the ignition switch is on, that all attachments are disengaged and that the transmission is in neutral. Most machines have safety mechanisms that will not allow them to start otherwise. Consult your owner’s manual for the starting procedure for your machine.
Make sure the spark plug wire is firmly attached to the spark plug.
If it still doesn’t start, check for a spark by removing the spark plug and grounding the hex part of the spark plug to a bare metal part of the engine. Remove any spilled gasoline that is nearby first, then spin the engine by pulling the rope or turning the key. You should see a blue spark jump across the plug gap. If you have a good hot spark, skip to the carburetor section.
lf the spark is yellow and weak, or there is no spark then the first thing to do is try a new spark plug. Don’t try cleaning the old one. Set the new plug gap to the proper spec (usually 0.030) and check for spark again. If you do see a spark, install the new plug and try to start the machine.
If there’s still no spark, try cleaning and setting the points on older machines, or replacing the electronic ignition module on newer machines. Before replacing the old module test it by disconnecting all the wires from the module terminal that connect to the kill switches and recheck for spark, if you do see a spark then a wire or switch is probably defective. Also check the flywheel key. That affects the spark timing, usually the key will need replacing if you strike something while mowing and the engine stops.
Checking the carburetor and fuel system
If the fuel is fresh, you have a good spark and still won’t start, you must make sure that fresh gasoline is getting to the carburetor. Make sure that the fuel shutoff valve (if present) is opened, and that the fuel line is not plugged or kinked.
Also be sure the fuel cap vent is open and any screens in the tank are clear of debris. If fuel can flow to the carburetor, carefully place 1 teaspoon of gasoline down the spark plug hole (or a add shot of starting fluid into the carburetor throat). Re-tighten the plug and try to start the machine. If it runs for a second or two, then quits, chances are the carburetor needs to be serviced (disassembled and cleaned inspected, then rebuilt) or you have an air leak somewhere.
Make sure all mounting screws or bolts are snug and gaskets are not missing sections. If the carburetor is a bowl-type check for water in the bottom of the bowl (but do not let the float swing all the way down or the float needle will fall out!).
Hopefully, this will give you a little insight in what to look for if your mower won’t start. Most starting problems are fuel related because the previous year’s fuel wasn’t removed. You may have gone years without removing the fuel at the end of the year without having any starting problems. There is a chemical process called varnishing that puts a coating on the inside workings of your fuel system. Over time this process continually worsens until your system becomes inoperable.
Precautions
Gasoline can ignite very easily. Work only in well-ventilated areas and away from sources of heat, sparks, and flames. Always wear safety glasses, and be careful of sharp blades. Keep a fire extinguisher nearby.
Your Lawn Mower Isn’t Getting Gas: Fix it NOW!
Your lawn mower may begin running sluggish, act like it’s going to shut off, or not start. These are all symptoms of a lawn mower not getting fuel. Removing a fuel restriction will get fuel to the engine so it runs at its best.
A lawn mower isn’t getting gas because the fuel is old, the fuel filter is plugged, the fuel lines are clogged, the fuel cap doesn’t vent, the carburetor is dirty, or the fuel pump doesn’t function properly.
Take safety precautions when working with your lawn mower. You can find specific safety guidelines for the mower in your operator’s manual.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
Reasons Your Lawn Mower Is Not Getting Fuel
Bad or Old Fuel in a Lawn Mower
Fuel starts to lose its combustible properties and breakdown as quickly as 30 days after purchase. Always purchase fresh fuel and consume it right away. The negative effects of old fuel occur in both gasoline and diesel fuel.
Gas for Gas-Powered Lawn Mowers: Using old fuel in your lawn mower can cause problems that will prevent fuel from getting to the engine.
Most types of gasoline sold today include ethanol, a corn-based product to make fuels a little more environmentally friendly. Ethanol naturally attracts moisture which can leave behind a sticky substance that clogs the fuel system.
In addition to creating clogs, the water and ethanol mixture can corrode fuel system components. As gasoline ages, the mixture separates from the gas and sinks to the bottom of the fuel tank. This solution will run hot causing potential damage to the engine.
Use the right gasoline in your gas-powered lawn mower. This is unleaded gasoline with a minimum octane rating of 87 that contains no more than 10% ethanol. Less ethanol in gasoline or even an ethanol-free fuel is best. Read more about the right gas for your lawn mower here.
Diesel for Diesel-Powered Lawn Mowers: Sludge can build up at the bottom of diesel tanks, even those at the fuel station if diesel sits around for long periods. Bad diesel fuel will appear dark in color.
You can also identify old diesel fuel by looking at the fuel filter. The fuel filter will appear dark in color from straining the sludge from the fuel coming out of the mower’s tank.
FIX: When you find old fuel sitting in your lawn mower, drain the fuel tank. A siphon pump works great for this. Make sure you have a fuel container to collect the old fuel. Set aside the old container of fuel to be properly disposed of at a recycling facility.
Refill your fuel tank with fresh fuel. Add a fuel additive to your fuel to stabilize and clean the fuel system. I use a product called Sea Foam Motor Treatment. You can read more about the advantages of Sea Foam here and why I use it in every tank of fuel.
Plugged Fuel Filter on a Lawn Mower
The fuel filter is placed on your lawn mower to filter out dirt and sediments from entering the fuel system and into the engine. When the filter becomes plugged, fuel is no longer able to pass through the filter and through the fuel system.
The filter should be changed at least once a year to keep it in good working order. You may need to change it more frequently when running old or dirty fuel.
FIX: Replace a plugged fuel filter. There should be an arrow on the plastic housing of your fuel filter housing.
Make sure you install the filter correctly with the arrow pointing in the direction of the mower’s fuel flow. This means the arrow should be pointed toward the carburetor and away from the fuel tank.
Clogged Fuel Lines on a Lawn Mower
The sticky deposits that form from the evaporation of ethanol and water can clog the fuel line. To identify a clogged line, you will need to check each section of the line for the restriction. Once you find one, remove the clog by using these steps:
FIX: Remove a lawn mower fuel line clog
- Use the fuel shut-off valve to shut off the fuel supply. You’ll find the valve located at the bottom of your fuel tank.
- If your mower doesn’t have a fuel shut-off valve, use pinch pliers on your line to stop fuel flow.
- Identify a section of the fuel line to check and remove the end of the line from the component (the end furthest from the fuel tank). Place the end into a container to collect fuel.
- Start your fuel flow by opening the fuel shut-off valve or removing the pinch pliers.
- Watch for fuel flow into the container. If you aren’t getting fuel flow, make sure the container is placed lower than the fuel tank because fuel cannot run uphill without the help of a fuel pump. If you still don’t get good fuel flow into the container, you need to remove the clog.
- Shut off the fuel supply and remove the clogged section of the fuel line.
- Spray carburetor cleaner into the line to loosen the restriction.
- Blow compressed air through the line to remove the blockage.
- Repeat spraying carburetor cleaner and blowing compressed air through until the clog is removed.
- If you are unable to remove the clog, replace the line with a new fuel line.
Bad Fuel Pump on a Lawn Mower
You will have a plastic or metal fuel pump on your lawn mower when the fuel tank sits lower than the carburetor. When a fuel pump is needed, most lawn mowers use a vacuum fuel pump. This type of pump builds pressure using the vacuum in the crankcase. It uses this pressure to get fuel to the carburetor.
When the fuel pump has cracks, is damaged, or leaks, you must replace it with a new one. If you don’t notice any damage or leaking of the fuel pump, it’s time to troubleshoot the fuel pump to ensure it is working correctly.
FIX: Confirm the fuel pump is functioning properly by, first, checking to make sure you are receiving fuel flow to the pump. You may have already reviewed this in the previous step if you checked your fuel lines for blockage. If you didn’t, refer to the steps above to check for fuel flow to the pump.
Once you have confirmed you are getting sufficient fuel to the fuel pump, remove the fuel line off the carburetor and place it in a container. Next, start your fuel flow and start your mower.
You should see a steady or pulsating stream of fuel flowing out of the fuel line signifying your fuel pump is working correctly. Replace a bad pump.
If the mower uses an injection fuel pump, refer to the operator’s manual for manufacturer specifications for the fuel pressure.
Use a fuel pressure gauge to find the pressure reading for the fuel flow out of the pressure line. A fuel pump with a pressure lower than the manufacturer’s specifications must be replaced.
Replace a bad fuel pump that is damaged or is not pumping a stream of fuel out of the pump.
Dirty Carburetor on a Lawn Mower
A gas-powered lawn mower uses a carburetor to regulate the fuel that is mixed with air to form combustion in the engine cylinder. You will find your carburetor mounted to the top or side of the engine block. It is usually below or behind your air filter.
When the carburetor is dirty, the components of your carburetor, including the fuel jet, can become clogged preventing your lawn mower from getting fuel to the cylinder.
First, to help identify a carburetor problem, make sure you are getting fuel to the carburetor. Next, remove your air filter for the air filter housing and spray a little carburetor cleaner into the air intake.
Start your engine to see if it will run. If the mower starts, runs, and then shuts off, you will need to remove your carburetor and take it apart for cleaning.
This is a test to make sure your mower will start using the carburetor cleaner. If it doesn’t, you may have a problem other than a fuel issue.
Refer to my guide on common lawn mower problems for a chart to better identify your mower’s problem.
FIX: Clean the carburetor. Most homeowners can do this if they are a little mechanical and don’t mind working with small parts.
Bad Fuel Cap on a Lawn Mower
The fuel tank needs to vent through the fuel cap so it doesn’t act like a vacuum restricting fuel from leaving the fuel tank. When the fuel cap vent is clogged it prevents air from passing through the cap.
To check if your fuel cap is the problem, remove the cap, start, and let your mower run. If it runs fine, reinstall the fuel cap while continuing to allow your mower to run for a while.
If it eventually shuts down with the cap installed but starts and runs again as soon as you remove the cap, you may have a problem with a clogged fuel cap.
FIX: You can attempt to clean your cap to remove the cap. This doesn’t always work and you will have to purchase a new fuel cap.
Still Having Problems with Your Lawn Mower?
Lawn mower ownership doesn’t come without its frustrations. Own a mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting, and overheating.
For mower troubleshooting, check out my guide Common Lawn Mower Problems: Solved.
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