Lawn Mower Starts Then Dies

My Lawn Mower Starts Then Dies: What’s Wrong?

Ahhh…the smell of fresh-cut grass. There’s really nothing like it. However, it’s pretty frustrating to be all ready to tackle those tall green blades only to have your mower fire up and then sputter out. If your lawn mower starts then dies, you want a quick answer about what’s to blame, and what to do to fix it. I’ll share the 4 most common causes to this mower problem and what you need to do to address each.

When your mower starts then dies it can feel like you’re alone, but this problem is more common than you might think, and the fix can be an easy one.

Let’s take a look at the four most common reasons behind that false start and how to fix them.

Causes for Lawn Mower Starting then Dying

If your lawn mower starts, runs briefly, then dies these are the four most common reasons that’s happening:

  • Dirty carburetor / clogged carburetor bowl
  • Old gasoline that has gone bad
  • Dirty or defective spark plugs
  • Too much oil in your resevoir

Below I’ll get into each potential problem, why it can result in a mower that starts then dies, and what you should do to fix it.

Dirty Carburetor or Clogged Carburetor Bowl

When your lawn mower starts then dies, your carburetor is most likely involved somehow.

Mower Starts Then Dies

Think about it. If you live in a northern region, your mower sits all winter … waiting months without any action.

And, if you live in a more temperate zone, your mower works hard year-around.

In both cases, your carburetor is going to need a little TLC.

What’s so important about the carburetor?

Your engine needs a steady flow of gasoline to run correctly. The carburetor is responsible for mixing gas with just the right amount of oxygen to create combustion.

This combustion supplies a continuous rotation of the crankshaft that is necessary to run the mower’s engine.

If your carburetor is dirty or the carburetor bowl is clogged, the process above is compromised, and your engine may start up, but it will not run properly and may die shortly after you pull the cord.

How do I fix it?

Your dirty carburetor needs a good blowout with an aerosol can of carburetor cleaner. This will cost you less than $10 and will last for a season or two. I use the WD-40 Specialist Fast Acting Carb/Throttle Body Parts Cleaner (Amazon link). This cleaner uses a solvent formula to breakdown carbon contaminants, leaving your carburetor clean and gum-free. I give my mower a shot of that every time a mow, right before pulling the cord, and recommend that you do the same.

The only drawback to this particular cleaner is it does not have a straw for targeted spraying. If you need a more precise application, Gumout makes a cleaner (Amazon link) that will do the trick with its jet spray applicator.

You can purchase either product locally, or online.

Now for the process.

Unscrew the carburetor bowl and give it a once over with the cleaner. Be sure to clean the screw and hole with the carburetor cleaner as well. This is where the directional spraying straw is particularly handy. When reattaching the bowl, don’t over-tighten the screw. This could strip the threads enough to distort the seal.

What I Do

For carb maintenance, give a light spray near the air intake hole for your mower’s engine just before you start it up. This is typically just behind the air filter. Remove the filter, give the hole a spray, then replace the filter.

When you start the mower, it’ll be pulled into the engine and clean deposits in your carb.

Old Gasoline in Your Mower

You know your mower can’t run without gasoline, but the quality of the gas is equally important.

If the gas in your mower has been sitting inactive for a while, evaporation has most likely created a damaging residue.

Old Gas in Your Mower Can Cause it to Start Then Die

This residue leaves particles that clog your mower’s internal parts.

The end result is restricted gas flow, which means your mower can start and die shortly thereafter. Sometimes, your mower won’t start at all.

How do I fix it?

If your mower tank is less than half full of old gas, you might try adding new gas to dilute the impurities. If the old gas is more than half of a tank, it would be best to siphon it out and fill the tank with fresh gasoline.

In both cases, adding a stabilizer such as Sta-bil Fuel System Stabilizer (Amazon link) is a smart idea. Stabilizers prevent the clogging residue for up to two years, and at around $10 a bottle, they are an inexpensive additive that can keep your mower running like a champ.

Always read the directions to know the proper fuel to stabilizer ratio for your mower.

What I Do

I used to mix Sta-bil into my fuel, but now I just pay a little extra for 4-cycle TruFuel – an ethanol free gas product that can sit for years without going bad.

It’s more expensive than regular gas mixed with Sta-bil, but a couple of larger cans will get my Honda self-propelled mower (this one from Home Depot if you’re curious) through the mowing season up here in New England, and I like the peace of mind that comes with knowing my mower and snow blower always start on the first pull, and I don’t have to worry about bad gas giving me problems when I’m ready to mow or need to clear the driveway.

You can buy it online, or locally at Home Depot or some local hardware stores.

Dirty or Defective Spark Plugs

Spark plugs supply the “spark” that ignites the air/fuel mixture in your engine.

Spark Plug

This small explosion makes your engine produce power.

The spark plugs are an essential component of your mower’s ignition system. If they are dirty or faulty, they will not spark, and your mower will not start, or may start and then quickly die.

How do I fix it?

Your mower’s spark plug(s) are easy to find. In most walk-behind mowers they’re covered with a black cable and right in the front of your mower.

Location of Spark Plug in Walk Behind Lawn Mower

You’ll need a socket wrench of the right size to remove your plug (check your manual to find the correct size for your mower/spark plug).

If your spark plugs are not too heavily coated with build-up, you can try cleaning them. You should never clean a spark plug with a shot-blasting cleaner. A wire brush and appropriate cleaner will do the trick if the plug is just dirty.

However, if your mower’s spark plug looks filthy or appears to have a dark carbon residue, you might be better off replacing.

This is an easy job and it’s inexpensive – a new spark plug with be $8-9 and your size is probably available locally.

What I Do

Spark plugs should be replaced every year or two for problem-free mowing, and I do mine annually as part of my spring mower maintenance.

I get a new air filter and change the oil in my mower at the same time. This runs me about $20 total, takes me about 15 minutes, and keeps my mower in perfect working condition.

Replacing Your Spark Plug

Removing your spark plug is an easy job anyone can do. Simply unhook the spark plug wire and remove the old plug with a spark plug socket. 

Replacing a spark plug can be a bit more challenging for a first-timer, but I still consider it an easy job.

Lawn Mower Spark Plug

Use a spark plug gauge to measure the gap between the two electrodes at the tip of your spark plug. Check for the specifications for your model to know the recommended size of the gap.

If necessary, use a spark plug gauge to adjust the gap by gently bending the curved electrode. When the gap is correct, the gauge will drag a bit as you pull it through the gap. 

Now you can install the new plug and attach the spark plug lead.  Be careful not to over-tighten on installation.

If you have never done this before, there are several videos online that can be of great assistance, but my advice is that as soon as it starts to feel snug, give it no more than another quarter turn to prevent damage.

Too Much Oil in the Mower’s Reservoir

If your carburetor is clean and the spark plugs are firing, the problem might be too much oil.

I believe it’s human nature to want to over-fill a lawn mower’s oil reservoir, especially if you’re not particularly handy. You feel so accomplished that we’re doing the job yourself that you go overboard and over-fill the tank.

Too Much Oil in Lawn Mower Reservoir

It happens, and it’s not the end of the world (or your mower).

White smoke coming out of the engine is a tell-tale sign that excessive oil is the culprit.

If a lot of smoke is coming out, your mower might be running, but not for long. In this case, the excess oil will eventually drown out the engine and cause it to die.

How do I fix it?

This is actually an easy fix. If you have too much oil, you just need to drain some. You can use a siphon, or (if you have a walk-behind mower) you can tip your mower and drain the oil from the hole where you add it.

What I Do

I’m guilty of overfilling the oil tank sometimes too, so I’ve learned to go slow when I add oil. I check, and check again with the dipstick and gradually bring the level up to the proper place.

If you have overfilled your oil tank, I advise that you use a dipstick to measure the amount of oil in the reservoir before removing it, and then again after to make sure you get the right level.

Not enough oil is another (and more serious) problem, and you would not want to inadvertently trade one issue for another.

After draining some oil and checking to see if you have an adequate amount, start the mower again.

If the mower fires and stays running without the billowing puffs of white smoke, you have corrected your problem.

Lawn Mower Starts Then Dies: When it’s Time to Call a Professional

If you have tested all of the methods I’ve shared for fixing your lawn mower that starts and then dies, hopefully your problem is solved.

But if not, it might be time to throw in the shop towel and call a professional.

Lawn Mower Starts Then Stops

The following are other issues that could be keeping your mower from running properly.

More Serious Reasons Your Lawn Mower Starts Then Dies

  1. Worn out carburetor:  If your carburetor is more than dirty, it might be time to replace it.
  2. Faulty choke: Unless you are extremely handy, identifying this problem and restoring the delicate balance necessary to get your engine purring like a kitten is another issue for the experts.
  3. Gas tank or gas line blockage: Anytime your gasoline is not getting to the engine, your mower will not run properly. A blockage of any kind that prevents the constant flow of gas is a problem that might take a trained eye to identify and fix.

The average weekend warrior with limited knowledge on the matter will probably feel more comfortable hiring someone with the experience and the tools to get the job done right.

I recommend that you start by checking your mower’s warranty. If it’s covered, a repair may not cost you anything. Some companies will send someone right to your home, or come to pick up your mower to save you time.

If your mower isn’t covered by warranty, find a local small-engine repair shop that has good reviews. These guys can fix almost anything, and their prices are typically lower than you’d expect.

Preventing Mower Problems

The best way to ensure your mower will fire up and run like a champ is to put preventative measures in place. 

I have tips for winterizing your mower, and a spring maintenance checklist that you can check out if you’d like to learn more.

Mower Starts Then Stops

To summarize those here, however:

  1. Clean your air filter regularly (replace it annually).
  2. Change your spark plugs every 1-2 years.
  3. Keep stored oil and gasoline clean. Use a stabilizer in your gas to keep it fresh for up to two years, or pay extra for 4-cycle TruFuel.
  4. Keep your engine clean with an engine degreaser.
  5. Use the dipstick and don’t overfill your oil reservoir.
  6. Keep your carburetor clean with a carburetor cleaner spray.

Performing regular maintenance on your mower is the best way to keep it running smoothly, and investing a few bucks per year in this is worth it.

You’ll avoid headaches, repair costs, and your mower will last a long time, starting right up when you need it.

If you do encounter a problem with your lawn mower, decide if you are comfortable with trying to fix it yourself.

If the issue seems to be something beyond the basics, don’t hesitate to call a professional. There’s no shame in this, and sometimes do-it-yourself repairs are just not worth the time, energy, or frustration.

But if you are up for the challenge of fixing the problem yourself, the above guidelines provide a good starting place, and online videos may also be useful. I think YouTube is a great resource.

The main thing is that you get your mower fixed so you can get out there and make your lawn the envy of the neighborhood.

by

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.

17 thoughts on “My Lawn Mower Starts Then Dies: What’s Wrong?

  1. deborah henry

    Thanks! This was a really great article! I have to add that if you can get ethanol free gas by all means do. And I have another question. How do you get the lawn mower blade off of a lawn mower? Even with heavy wrenches I can’t seem to do the trip

    • Thanks, Deborah!

      Totally agree about ethanol-free gas. I use TruFuel and while it’s pricey my mower can sit all winter and starts on the first pull every time.

      Great question on the mower blade! I’ll plan to do a full article on that subject, but there’s a trick where you need to brace the blade while using the wrench. You can YouTube it and find a demonstration. I also keep a can of liquid wrench spray on hand – you can pick it up locally at a hardware store, and that can loosen even the most stubborn, rusted nuts and bolts. Good luck, and be safe while working with your mower blade!

  2. Tiffany hamby

    Did all the tips cleaned the carb changed the oil and changed the spark plug. It will start but then die as soon as it starts. What do I do now?

    • Hey, Tiffany!

      Have you drained your gas tank and put fresh gas in? And did you check your air filter?

      Those are the next two items I’d check just to rule out some of the most common ones. If that’s not it there may be a problem with the mower’s choke. A lot of modern mowers have auto-choke and if that gets out of whack the mower will die after starting up. This is typically a quick fix for a small engine repair shop.

      Good luck!

  3. jim evers

    All the remedy’s you recommend are wrong for Cadet mowers shutting off after the key returns to the run position. You seem to think it is fuel related….but it is a electronic issue. Resolve my problem, without resorting to “fuel”.

    • Hi Jim,

      Thanks for sharing your experience with your Cadet mower. It’s tough to diagnose every possible mower problem in a single article, so I tried to cover the issues that are most common here. Hopefully if someone else is having trouble with their Cub Cadet and the article above doesn’t help them your tip about looking at the electrical system will save them some time! Thanks for the comment.

    • Hamish MacGowan

      Robert, You are a dead set LEGEND. I was having all sorts of problems with my lawn mower. I ran through the usual checklist which pretty much always produces a result. Couldn’t work it out and then I came across your comment regarding “Blocked Vent”. A couple of firm taps later and my mower sprang back into life. Hasn’t missed a beat yet. You’re the “Mower Whisperer”. Keep up the good work. Best regards, Hamish.

  4. Jose Benavides

    My tractor lawn mower will run for a few minutes till it warms up then acts like it is out of gas. So the warmth expands something to chock the fuel out???

    • Hey, Jose!

      To me it sounds like it may be a clogged vent on your tractor’s gas cap. The cap has a small hole in it which allows some air in/out of the tank so that there’s the right amount of pressure so that the fuel is mixed evenly as your engine runs. If it’s clogged with dirt or dust or something then air can’t get in as your mower burns its fuel, and so after running a while the air/gas ratio in the tank and the pressure is off. This can create this surging where it sounds like your mower is struggling to get gas.

      if you can’t see a blockage, an easy way to check if this is the problem is when that happens next, stop the mower, open up the gas cap, then put it back on. This normalizes the pressure in the tank by allowing air to get in when you remove the cap. If the mower is fine when you start it back up again, then this blockage is definitely the problem – find the hole in your cap and something that will slip through it and get that cleaned out and you should be good to go. I had a John Deere growing up that had this issue all the time as it got older, so it’s not uncommon.

      Hope this solves the issue for you! Good luck.

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