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

If you’re reading this article, I’m willing to bet it’s because you’ve encountered a relatively common yet very annoying problem with your lawn mower.

Sometimes, lawn mowers reach the end of their lifespans after many years of reliable use, and in these cases, it’s time to purchase a new model.

However, it can be confusing when your lawn mower starts up just fine, only to suddenly stop dead in its tracks. Should you try and salvage the mower or start looking for a replacement?

My Lawn Mower Starts Then Dies What’s Wrong

Well, that depends on the underlying cause. There are a few different reasons why a lawn mower might fail after starting up, and while some can be easily rectified, others will call for professional assistance or a new machine.

In today’s article, I’ll be covering all the most common reasons why lawn mowers start and then die, complete with advice on how to approach the problem.

Hopefully, by the end of this piece, you’ll have a clearer understanding of what’s going on with your lawn mower and what you can do to fix it!

Reasons For Lawn Mower False Starts

So, your lawn mower is starting up and then failing immediately afterward. That’s very frustrating, but luckily, in most cases, false starts in lawn mowers are caused by relatively minor problems that you can fix at home.

In this section, I will be covering the 4 main causes of a lawn mower starting and dying. Be sure to check for all of the issues listed below before you move onto our next section, which explains when you should seek professional guidance.

Carburetor Blockage

Easily the most common cause of lawn mowers false-starting is a blockage in the carburetor.

The carburetor is arguably the most important component of a lawn mower’s engine. A lawn mower’s carburetor is responsible for exposing the correct amount of fuel to oxygen in the engine’s cylinder, which results in combustion.

Combustion is what lawn mowers rely on to run smoothly because it powers the crankshaft. Without it, the motor can’t run consistently.

Of course, if your lawn mower’s carburetor is blocked (usually by old fuel residue), oxygen won’t be able to circulate through it properly. This weakens the combustion reaction, which can result in false starts.

So, how do you check the condition of your carburetor and how can you rectify this problem?

Repairing-mower

The first step is to locate the carburetor and see if it is, in fact, blocked or dirty. Usually, lawn mower carburetors are situated near the air filter.

Once you’ve found the carburetor, you’ll need to unscrew the bowl (which looks like a small-scale fuel tank bolted onto the carburetor).

The bowl is where most of the old fuel residue collects, so if a carburetor blockage is responsible for your lawn mower’s temperamentality, you should be able to see the proof quite easily.

The easiest and most cost-effective way to deal with a blocked carburetor is to invest in some carburetor cleaning spray.

These are typically solvent-based sprays that dissolve contaminating substances, leaving your carburetor clean and unobstructed.

Usually, these solvents come in aerosol cans, and some have precision-enhancing straw nozzles for maximum ease of use. You can find high-quality carburetor cleaners for very reasonable prices through retailers such as Amazon.

When you’ve chosen your ideal carburetor cleaning solution, all you have to do is spray the carburetor bowl thoroughly, including the bolt and the corresponding hole.

Then, remove the air filter from the back of the lawn mower and spray some of the solution into the air intake chamber. Just remember to put the filter back on before you try starting up the engine!

Faulty Spark Plugs

If cleaning the carburetor doesn’t work, it’s possible that the problem with your lawn mower is a faulty spark plug.

Spark plugs work in conjunction with the carburetor inside a lawn mower to make the necessary combustion reaction happen. In addition to oxygen and fuel, you need a spark to ensure ignition. This is the role of the spark plugs in your lawn mower.

As you can probably imagine, if one or both of your spark plugs are either damaged or dirty, this can create a serious obstacle to your lawn mower’s ability to start up properly.

spark plug

Thankfully, this is another issue that’s relatively easy to sort out from the comfort of your own backyard.

With most lawn mower models, the spark plugs are located at the front of the machine. Although they’re easy to spot, you will need to make sure that you have the right tools to remove them.

Unlike your carburetor bowl, the spark plugs won’t be screwed or bolted onto the lawn mower, so you’ll need a wrench (usually a socket wrench) to remove them.

Socket wrenches come in various sizes, so you’ll need to know which size is required. This information should be provided in your user manual, so consult this document if you’re unsure.

Alternatively, if you can’t find your user manual, check the manufacturer’s website for a digital copy or contact customer support.

Now that you have the right kind of socket wrench, you can go ahead and detach your spark plugs from the lawn mower and inspect them for damage or blockages.

How you should proceed from here really depends on how much residue is present. If there’s only a light coating, you might be able to clean your spark plugs well enough to ensure a proper startup.

However, many experts actually recommend just investing in some new spark plugs, especially if the residue has built up into a thicker coat.

The reason for this is that even if you clean your spark plugs really thoroughly, they’re still unlikely to return to their full functionality.

Spark plugs are quite affordable as far as lawn mower components are concerned, so replacing them shouldn’t put you out of pocket and will ensure superior performance.

Unfortunately, spark plug replacement isn’t a particularly beginner-friendly task. With that being said, there’s no reason you can’t attempt this process yourself with the help of some simple instructions.

Each spark plug will have a designated pair of electrodes, which need to be a certain distance apart. The recommended distance between electrodes should be specified in your user manual. You can use a spark plug gauge like this one to measure the gap.

If the gap between the electrodes is either too small or too wide, you can gently bend the already-curved electrode until the correct measurement is achieved. Then, you can go ahead and fit your new spark plugs using the spark plug lead.

Tighten the spark plugs enough so that they feel secure, but be sure not to make the attachment too tight or you could actually damage the plugs.

replacing lawn mower spark plug

Unchanged Fuel

Forgetting to change out the fuel in your lawn mower is one of the most common reasons for startup failures, but thankfully, it’s also one of the easiest to resolve without professional help.

Chances are, if your lawn mower is starting and dying in quick succession after a long period of inactivity, old fuel is to blame.

If it’s been a while since you’ve mowed your lawn (no judgment here!) and your mower has been sitting in your garden shed full of unused fuel, I’d actually recommend checking the fuel tank first before you look at the carburetor or the spark plugs.

When fuel (especially gasoline) sits in a lawn mower for a long time, it begins to evaporate. As this evaporation takes place, residue forms inside the fuel tank.

Just as fuel residue can cause blockages in carburetors and clog up spark plugs, it can begin to obstruct the fuel tank, hindering the movement of gas through the ignition system.

Before you start frantically changing out your fuel, though, take a moment to assess how full your fuel tank is.

If you don’t have too much fuel left (less than half of the tank’s capacity), you might not need to drain the existing fuel. Instead, you can try topping up the tank with fresh fuel.

This may have a diluting effect on the residue inside the tank, allowing obstructions to resolve themselves naturally.

However, if your fuel tank is still mostly full, adding more fuel is unlikely to dilute impurities effectively. In this case, you’ll need to drain the remaining fuel and fill the tank up all the way with fresh fuel.

When you fill up your fuel tank, I also recommend adding some stabilizer to the tank to prevent future blockages, but I’ll go into further detail on this in our maintenance section (see below).

pouring gasoline into mower

Excess Oil

If none of the above suggestions have fixed the problem with your lawn mower, don’t despair – there’s still one potential cause I haven’t covered yet.

It’s easy to accidentally overfill your lawn mower’s oil tank, especially if you don’t have a convenient measuring tool such as a dipstick on hand.

While overfilling your oil tank might not sound like a big deal (and in most cases, it’s not), too much oil can be overwhelming for the lawn mower’s engine. The result is usually a lawn mower that won’t start or starts and then dies – plus a lot of smoke.

If, in addition to starting and stopping, your lawn mower is producing white smoke, you can be fairly certain that excess oil is the problem.

Seeing smoke pouring out of your lawn mower can be alarming, but don’t panic. Wait for the system to cool down and use a siphon to drain some of the excess oil.

Use a dipstick to measure how much oil is in the tank and consult your user manual (or the manufacturer’s customer service department) regarding the tank’s official capacity.

If you don’t have a siphon and your lawn mower is a walk-behind model, you can opt for the less precise but equally effective draining method of tipping the machine so that oil pours out of the hatch on top.

When To Seek Professional Assistance

If you’ve tried all of our suggestions from the previous section with no luck, the chances are, your lawn mower issue is being caused by more complex internal issues.

If this is the case, the best course of action is to take the machine directly to a professional who can diagnose and, if possible, fix the problem.

repairing lawn mower

If your lawn mower’s warranty hasn’t yet expired, your first port of call should be the manufacturer’s customer service center. If your warranty is ongoing, you should

When it comes to professional lawn mower repair services, you’ll have different options available to you depending on your place of residence.

There are companies that provide services exclusively related to lawn mowers. Others offer wider specializations, such as garden machinery or general motor repair. A quick google search of lawn mower repair services in your area should bring up the relevant information.

Although you shouldn’t attempt further investigation yourself after ruling out the 4 problems detailed above (for your own safety and that of your lawn mower), there are a few diagnostic outcomes you can expect following professional inspection:

Carburetor Wear

A blocked carburetor is quite easily fixed, but certain levels of wear and tear are difficult to come back from when it comes to functionality.

If your lawn mower’s carburetor is badly damaged or simply worn due to age, it will need replacing.

If you’re a very handy person, you might be able to replace the carburetor yourself. However, since you’ll probably need assistance to find out if it’s truly worn out in the first place, you might be better off letting a professional handle this part of the process.

Clogged Fuel System

I’ve already discussed how old fuel can negatively impact the ignition system inside your lawn mower. I’ve also touched on ways that you can rectify this problem, including adding fresh fuel to a smaller amount of old fuel or replacing the fuel altogether.

With that being said, blockages caused by fuel residue can sometimes be more severe and impact components of the engine that are difficult to access. In these situations, partially or even completely replacing the fuel is unlikely to solve the issue.

Professional motor or lawn mower repair services are well equipped to tackle serious blockages. So, if you think that your fuel tank or fuel line is blocked beyond home intervention, calling in a professional is the most sensible step to take.

Damaged Choke Valve

The choke valve, also simply referred to as the choke, is a lawn mower component designed to regulate airflow during startup. Specifically, its job is to reduce the flow of air into the combustion chamber, which allows more fuel to enter the chamber.

If your lawn mower’s choke valve is damaged or broken, you can see how this would have a detrimental effect on the motor’s ability to start and stay running.

Unfortunately, the choke valve is a fairly intricate and complex component of the average lawn mower, which makes it unlikely that you’d be able to fix or replace it yourself unless you have some form of engineering experience.

For this reason, professional assistance is the first port of call for most people when they suspect that the lawn mower’s choke may be compromised.

Preventative Lawn Mower Maintenance

Preventative Lawn Mower Maintenance

With the help of the information provided above, you should be able to either fix your lawn mower’s startup problem or direct the issue towards the right professional service.

But you might be wondering what you can do moving forward to prevent the same issue from arising in the future. Luckily, the key to long lawn mower life is simple: thorough and proactive maintenance.

The cleaning and replacement tasks I’ve outlined throughout this article are effective solutions to the problem of false starts in lawn mowers. However, the majority of these tasks are best performed preventatively rather than after issues arise.

For instance, you should try to clean your carburetor regularly rather than only inspecting it when there’s a problem.

In fact, some experts recommend using solvent spray on your carburetor and bowl before each and every use of your lawn mower. This might sound tedious, but it’s a quick process and certainly much less annoying than dealing with a lawn mower that won’t start up properly.

Similarly, you should be regularly cleaning your air filter and replacing it on a yearly basis. Otherwise, it will become clogged and prevent proper air circulation, which is key to combustion and ignition.

If you don’t mow your grass very often, it’s a good idea to keep note of the last time you used your lawn mower and how much fuel is left in the tank.

If the fuel has been left to sit in the lawn mower for over 30 days, I recommend either topping it up with new fuel or changing it out completely, regardless of whether it seems to be starting up properly.

This will prevent excessive residue buildups and minimize the risk of internal blockages.

While I’m on the subject of fuel, getting into the habit of regularly adding a stabilizer to your fuel can go a long way in terms of maintenance.

A stabilizer is a solution designed to keep fuel fresh and residue-free for longer, so even if you forget to change the gasoline for more than 30 days, the stabilizer should mitigate the risk of clogged fuel lines. The STA-BIL Storage Fuel Stabilizer is an excellent choice, as is TruFuel 4-Cycle.

Spark plugs are another part of your lawn mower that you should replace regularly, just like the air filter.

Spark plugs typically last a little longer than the average air filter, but you should aim to replace them at least every 2 years. If you stay on top of spark plug replacement, you should hopefully never encounter startup failure as a result of dirty or damaged plugs.

A general engine cleanup is another important step towards ensuring the longevity of your lawn mower.

You can use a basic engine degreasing solution such as the Chemical Guys CLD_201 Signature Series Orange Degreaser to strip away any residue that could build up and cause a blockage later down the line.

This is definitely one of those problems it’s better to address before it becomes a significant issue since professional help is often required for deeper, more substantial lawn mower blockages.

Frequently Asked Questions

What Is The First Thing To Check If Your Lawn Mower Won’t Start?

You’ll get different answers to this question depending on who you ask, but in our opinion, it’s worth checking for problems that are easier to fix first.

The reason for this is to potentially save you time. It makes more sense to check if there’s residue in your fuel tank or if you’ve filled your oil tank too much before you start unscrewing your carburetor bowl or wrangling with spark plugs.

However, if neither the oil nor the fuel is the problem, I recommend checking the carburetor and spark plugs next.

Why Is It So Hard To Start My Lawn Mower?

Even if you don’t have a problem with your lawn mower dying after starting up, you may have noticed that the machine is having more difficulty starting over time.

If that’s the case, the good news is that the same problems that cause false starts in lawn mowers are the usual culprits.

When you’re struggling to get your lawn mower to start, turn your attention to the carburetor, oil levels, spark plugs, and fuel tank.

Final Thoughts

I hope that you’ve managed to find the solution or help that you need to fix your lawn mower’s startup issues. Using the information provided in this article, you should be able to plan your next diagnostic steps.

Remember, prevention is always better than a cure, so make sure you’re performing diligent maintenance on your lawn mower to stop this issue from coming up again in the future.

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