Lawn Mower Starts Then Dies – Troubleshooting

Lawn mowers can be hard to troubleshoot. If your mower is starting and then stopping, what should you do?

We’ve all been there. One day as you are pulling your lawn mower out of the shed to cut your lawn to the proper height, the engine suddenly stops working. When your mower dies on you like this, it’s not only a nuisance, it ruins your entire weekend plans. 

What could cause your machine to behave in this manner?

There are four possible culprits who could be robbing your lawn of its mowing session. And this article will go over all four of them. We’ll go over each potential issue and what causes it, as well as how to fix it so you can get back to work.

A very small and basic lawn mower equipment

1. Old Gasoline

Obviously, your lawn mower won’t run without gasoline. But, for the sake of argument, suppose you forgot to drain the gasoline before storing the lawn mower for the winter. Or perhaps you had to evacuate due to a hurricane (as I recently did) and were gone for an extended period of time.

That gasoline, however, evaporates over time and loses not only its potency but also forms a residue that can accumulate on the inside of the tank. This residue has the potential to clog the working parts of your lawn mower.

These clogs restrict the gas flow through the machine, causing it to start and die or not start at all.

How to Fix the Problem

You’ll need to do one of two things depending on your fuel level. If the tank is less than half full, try adding some fresh gasoline to dilute the impurities and free up the gas flow.

If your tank is more than half full, you must drain the old gas and refill it with new gasoline.

Whatever option you choose, you’ll need to mix a fuel stabilizer into the gasoline. For up to two years, a fuel stabilizer prevents the residue that caused the clogging in your lawn mower’s engine from accumulating. The stabilizers cost between $10 and $15 per bottle and are well worth the investment in order to keep your mower running.

A person pouring gasoline into the tank of a lawnmower

2. An Issue With the Spark Plugs

Spark plugs are the components that ignite the air/fuel mixture in your lawn mower’s engine and start it up. There is no combustion without the spark. Your lawn mower will not move without combustion.

There are a few issues that can arise with spark plugs. They may be filthy, defective, or simply worn out. Whatever the case may be, you must replace the spark plugs or your lawn mower will become a lawn ornament, which you did not intend.

How to Fix the Problem

Worn Out Spark Plugs

If you’ve had your spark plugs for more than two years without changing them, they’ve probably just worn out on you.

The plugs should be easy to find, particularly on a walk-behind mower. A spark plug cable should be located near the front of your lawn mower. To remove the spark plug, you’ll need a wrench or socket wrench that fits the spark plug.

After you’ve removed it, simply replace the spark plug and reconnect the cable. If the problem was worn-out spark plugs, the engine should start right up.

A person holding a spark plug from the lawn mower

Dirty or Defective Spark Plugs

Engines powered by gasoline are not the cleanest of machines. Over time, the various parts and pieces collect all kinds of gunk, residue, and buildup. Your spark plugs are no exception. So, if you remove your spark plugs and discover that they are dirty but not filthy, cleaning them with the appropriate cleaner and a wire brush may save you from having to buy new ones.

Simply take a wire brush and some WD-40 and get to work. However, if your plugs are extremely dirty or have a dark carbon residue buildup, it’s probably best to just buy a new spark plug.

If you need to replace the spark plugs, you should also change the oil, oil filter, and air filter while you’re at it. The entire package should cost no more than $30. It will also help to extend the life of your lawn mower.

3. Clogged Carburetor Bowl or Dirty Carburetor

When your lawn mower starts then dies, there is a good chance that a faulty carburetor is involved in some way. And, like the spark plugs, the carburetor is an important component of your lawn mower engine. It’s in charge of combining just the right amount of oxygen with the fuel in the gas tank to produce just enough combustion to power the engine while not blowing your lawn mower 50 feet into the sky.

This process can be hampered if your carburetor is clogged or dirty. And, as you are aware, without combustion, your lawn mower is nothing more than a lawn ornament.

How to Fix the Problem

Because the carburetor is one of those internal parts that is critical to the engine’s performance, you will need to clean it. To complete the task, I recommend using Gumout Small Engine Carb Cleaner. It has the power of an aerosol spray and a straw attachment for directing the spray into smaller areas.

Begin by removing the carburetor bowl from the engine by unscrewing it. Once you’ve removed it, clean it thoroughly with your preferred product. Make sure to clean the screw as well as the hole where the screw goes. This is where the directional straw comes in handy for these smaller areas.

When reattaching the carburetor bowl to the engine, be careful not to overtighten the screw and strip it. You may end up jeopardizing the seal.

Another useful tip is to spray your cleaner into the air intake hole of the engine. When you start the engine, the intake will suck the cleaner into the engine and clean up any residue that has accumulated in the intake. On most lawn mowers, the intake is located behind the air filters.

Dirty and dusty old lawnmower carburator

4. Too Much Oil in the Oil Reservoir

Too much oil in an engine is analogous to too much water in a human. It may appear to be a good idea at first, but too much oil in an engine or too much water in a human can cause the entire machine to fail.

When there is too much oil in the engine, the telltale sign is white smoke emitting from the exhaust.

How to Fix the Problem

Too much oil in the tank causes engine stalls and is a fairly simple fix. Simply take an oil dipstick and measure the engine oil level to determine how much to drain. The excess oil should then be sucked out. While siphoning, keep checking the oil level with the dipstick to see when it reaches the proper level. Allow the oil to settle for a few moments before attempting to start the engine.

You’re in good shape if you’re no longer seeing plumes of white smoke and the engine doesn’t stall. Go ahead and cut the grass.

Seek Professional Help

Hopefully, your issue falls into one of these four categories, which you can resolve on your own. If none of these work, you may need to seek the assistance of a professional small engine mechanic. Because things like a clogged fuel line, a faulty choke, or a worn-out carburetor may require replacement. And these are best examined by a professional.

Jeffrey Douglas
Jeffrey Douglas own a landscaping company and has been in the business for over 20 years. He loves all things related to lawns or gardens and believes that proper maintenance is the key to preventing problems in the first place.
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