Why a Lawn Mower Starts Then Dies + Troubleshooting Tips

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Using a lawnmower is a cost-effective way to maintain a lawn, as it requires minimal expenses such as fuel or electricity. However, they can break down in the middle of a job, which can be frustrating, especially for a first-time owner.

So, our experts detail everything you need to know if your lawn mower starts then dies to help you troubleshoot the problem.  

What is a Carburetor?

All compact gas-powered engines feature carburetors where air and fuel are combined. Carburetors on lawn mowers may look like simple equipment, but they are pretty sophisticated, especially considering how small the engines are.

To maximize performance, the air-to-fuel ratio (AFR) is made to achieve a 14.7-air portion to a 1-fuel portion. In fact, a mower’s performance degrades when this specific air-fuel ratio is altered.

Toro Lawn Mower carburetor

Engines can run lean (low on gas) if its fuel system is obstructed, if the carburetor is broken, or rich (with too much gas) if it has a dirty air filter.

Common Lawn Mower Carburetor Parts

Choke

A choke metal flap blocks the carburetor’s air intake. When an engine is cold, a richer fuel mix is just what it needs. The fuel mixture’s increased richness partially mitigates the chilly, thick air.

Choke On

When the choke is “on,” it restricts the flow of air, which causes the engine to receive a richer fuel mix and helps it to start more easily in cold weather or when the engine is cold. 

Choke Off

When a choke is “off” or “open,” it’s not restricting airflow into the carburetor. It allows the normal air/fuel mixture to enter the engine, which is necessary for the engine to run efficiently. 

removing lawn mower carburetor

Once the engine is warm, the choke is turned off, so the engine can operate optimally. It also prevents the engine from flooding due to the rich fuel blend.

Choke Plate

A choke plate is a carburetor that controls the amount of air that enters the carburetor. The choke plate is typically located in the carburetor’s air intake and is usually connected to a linkage or cable controlled by the choke lever or knob. 

Primer

You might not find a choke on your mower but a priming bulb. It achieves the same purpose as a choke plate by supplying additional fuel during cold engine starts.

Carburetor Jet

Ports are tiny, precisely drilled holes in a jet’s brass tube. The jet resides in the carburetor’s central chamber, and fuel is drawn into the engine via the jet’s portholes when the machine takes in the air.

The jet regulates the flow of fuel into the engine.

fixing carburetor jet

If the holes in the emulsion tube are clogged up, air and gas flow gets restricted, which can cause the mower to stall, lose power, or refuse to start.

Fuel Bowl

Included with every carburetor is a fuel bowl ready to be pumped into the combustion chamber whenever required. The jet in the carburetor draws fuel from the bowl through the narrow openings.

The fuel bowl is located behind the air filter; it has a bowl-like form and can be accessed without removing any other components.

Fuel Bowl Feed Bolt

Eventually, the bowl will become soiled with dirt and condensation and require cleaning. It may be sufficient to scrub the fuel bowl and fuel feed bolt simply. The gasoline feed bolt is not standard on all lawn mower models.

person holding lawn mower carburetor

This gasoline feed bolt is not included with all fuel bowls. A hollowed-out bolt with a fuel feed aperture is used to supply the jet engine with fuel. Your mower’s air filter, if it has one, ought to be spotless.

Needle & Float

The fuel bowl, float, and needle are the standard components of a carburetor’s fuel supply. In addition to being a float, the float has a needle with a rubber tip attached to it.

As the fuel level rises, the float will raise the needle to indicate the change. Once the gas tank is full, the float’s needle will press against the fuel flow port and close it.

Due to a deteriorated needle seal, either too much or too little gas will get through.

lawn mower carb float repair

The float and needle work together to regulate the gas entering the burner’s bowl, and poor engine performance is guaranteed in case of a supply problem.

Also Read: Where is the Carburetor on a Lawn Mower

Lawn Mower Starting then Dying: 15 Causes and How to Fix

1. Old/Clogged Carburetor

If your lawn mower starts then dies, it is likely related to the carburetor.

Mowers in northern climates spend the winter collecting dust,  having to wait for months before use. Also, your lawn mower puts in long hours every season if you reside in a somewhat mild climate.

clogged carburetor

Your carburetor will require some maintenance in any situation.

What is the Importance of the Carburetor?

Your car’s petrol tank must be constantly full for optimal engine performance. The carburetor adjusts the mixture of gas and air to produce combustion.

The combustion keeps the crankshaft turning in the mower’s engine. Your engine may start up if the carburetor is grimy or it has a clogged carburetor bowl; however, this will not operate efficiently and may shut down soon after pulling the starter cord if it is.

How To Fix

A can of aerosol carb cleaner is ideal for your dirty carburetor. You can get two seasons’ use out of this for less than ten dollars. 

To clean the clogged carburetor, remove the bowl’s screw and spray it down. In addition, you should also use carburetor cleaner for the holes and screws. The directed spraying straw comes in quite handy at this point. 

cleaning carburetor

Don’t overtighten the screw when putting the bowl back. The threads may get stripped out, which will cause the seal to become distorted.

Bonus Tips

A small spray at the intake pipe in the mower’s engine before starting it will help maintain the carburetor. Usually, this is situated right at the back of the air filter. Take out the filter, spray the opening, and then put it back in.

It will then be sucked through the engine then cleaned out of the carburetor when you start your mower.

2. Stuck Gas on Your Mower

You know your mower won’t work without gasoline, but you might not realize how crucial the gas’s quality is.

If your lawnmower’s gas has been sitting idle for a while, a harmful residue may have formed due to evaporation.

fixing mower gas tank

Particles left behind by this residue might clog the moving parts of your mower.

As a result, gas flow is restricted, and your mower may start but quickly die. You may find that you cannot get your mower started on rare occasions.

How to Fix

You could add new gas to your mower tank to dilute the pollutants if the old gas is less than half full. It is recommended to siphon out the old gas and replace it with new gas if the tank is more than half full.

Bonus Tip

You can also purchase an ethanol-free gas product that doesn’t go bad after sitting for years.

3. Faulty Spark Plugs

The “spark” that initiates the air/fuel blend in your engine comes from the spark plugs. You get power from your engine thanks to this tiny explosion.

lawn mower spark plug

These are integral parts of the ignition system. Mowers are susceptible to not starting or dying rapidly if they are filthy or malfunctioning.

Signs of Spark Plugs Issues

Some signs of a spark plug failure include decreased engine performance, rough idle, misfires, increased fuel consumption, mower fires, and difficulty starting the engine.

How to Fix

Cleaning the Spark Plugs

If the mower’s engine has other issues, these parts may become worn or destroyed. If you don’t find out what caused the damage before replacing the plug, the replacement spark plug will end up in the same position.

Evaluate the air filter, the fuel injector, the distributor case, and the gas mower’s fuel and air mixture as potential causes for the faulty spark plug.

Replacing the Spark Plugs

Taking out a dirty spark plug is a simple task that anyone can do. It’s easy to replace defective spark plugs; just disconnect the wire from the old plug and twist it out of the socket.

installing spark plug

Spark plug removing, and replacement is a simple task, albeit it may be more difficult for a novice.

Measure the distance between the electrodes of a spark plug with a plug gauge. You may find the suggested gap size in the model’s specifications.

Slowly bending the curved electrode on a lawn mower’s spark plug gauge can modify the gap if it’s too large or too small. To know if the gap is correct, you should feel some resistance as you pull the gauge through the opening.

Replace the old plug and reconnect the spark plug wire. During installation, make sure you don’t overtighten anything.

Bonus Tips

Several helpful videos are available online if you’ve never tried this before. To avoid permanent damage, stop turning the bolt after it feels snug.

cleaning mower spark plug

4. Oil Overfill

When you see white smoke rising from your exhaust, it’s a sure sign that your engine has too much fresh oil. 

Your mower won’t run for long if it’s putting out a lot of smoke. As the oil floods the engine, it will finally stop working. 

These are just potential issues that would happen if your lawn mower has too much oil, and there may be more, depending on how you use it. 

How to Fix

The solution to this problem is simple. If there is too much oil, it can be easily removed. Oil can be drained from the mower’s oil fill hole using a siphon or tipping it on its side if you use a walk-behind mower.

Bonus Tip

If you’ve overfilled your oil tank, you should use a dipstick to check the oil level before draining it and again afterward to acquire the correct amount.

Since there is also (and more importantly) a lack of oil, you shouldn’t make the mistake of trying to solve one problem by addressing the other.

5. Lack of Gas/ Low Oil Level

Our lawn care specialists recommend that If you suspect the fuel tank is empty or nearly empty, fill it up immediately. But make sure you know how much oil you can put in your lawn mower

lawn mower fuel cap

How to Fix

A fuel gauge may or may not be included in your lawn mower. Those unfamiliar with what’s in the fuel tank can get a quick glimpse. You must inspect the carburetor bowl and the fuel lines for obstructions to ensure the engine is getting the gasoline it needs.

6. Old or Bad Fuel

A lawn mower can perish after being used if it is fueled improperly. A typical tank of gasoline has a 30-day lifespan before it begins to degrade. Modern fuel contains compounds that degrade with time, robbing it of its once-great performance and heat.

Ethanol now makes up a significant portion of the fuel supply. Ethanol-treated fuels are notorious for absorbing atmospheric moisture.

How to Fix

Adding Fuel Stabilizer

A fuel stabilizer is an option. Before putting it in the gas tank of your lawn mower, mix the stabilizer well with fuel in the can. There will be less decomposition of fresh gasoline as a result of this.

Mix the Right Fuel
filling lawn mower with engine oil

7. Air Filter is Plugged

Another reason why a lawn mower starts then dies is that the air filter might be plugged. This can restrict airflow into the engine, leading to various problems.

How to Fix

Do a Routine Air Filter Change

Clean or replace the filter as needed and reinsert it properly. Ensure that it is securely placed before starting the lawn mower. It’s also recommended to check the filter regularly and clean or replace it as needed to ensure the engine runs efficiently.

Other Possible Reasons

8. Fuel Filter is Plugged

The fuel filter may become clogged if the fuel in the tank is old, unclean, or contaminated. Your car won’t be able to keep running since it won’t get enough fuel.

Add fresh fuel to prolong the fuel filter’s life. The gasoline filter should be changed once a year to prevent any issues with the fuel system.

9. Faulty Fuel Pump

A fuel pump’s seams or the pump itself can rust over time. A leaking fuel supply is a telltale sign of a failing pump, but internal damage might be difficult to detect without first putting the pump through its paces.

fuel tank of lawn mower

The ability to initiate and terminate fuel flow is essential for testing the fuel pump. If your mower has a gasoline shut-off valve, you can utilize that. If it doesn’t work, you can crimp the gasoline line using a pair of pinch pliers.

10. Blocked/Damaged Fuel Cap

A vent is built into the fuel cap for this reason. Your engine may not acquire fuel if the fuel cap vent is blocked or the cap is broken. If your cap doesn’t vent, it will cut off the gas supply.

Loosen the cap and start the mower to observe if it turns over, indicating a broken cap. If you can start your lawnmower with a loosened cap, enabling it to vent, you should get a new one.

11. Failed Ignition Coil

When a lawnmower gets heated, the ignition coil’s winding might come unwound and cause a short. It prevents the spark plugs from receiving the voltage required to ignite a spark. A lawnmower may die after prolonged use if this occurs.

testing mower's ignition coil

Checking for lack of continuity with an ohm meter might help you pinpoint a malfunctioning ignition coil. Change the ignition coil with a new one if you notice a break.

12. Broken/Clogged Cooling System

A cooling fin may get smashed or clogged with debris like grass and mud [1]. The engine block will overheat when this occurs because the fins cannot draw air from the surrounding area. There’s a risk that if this occurs, the lawn mower will overheat and stop working in the middle of cutting the grass.

To clean the cooling fins, you must first remove the engine cover. Fix the broken fins. Carefully clean the area surrounding the engine and the cover.

13. Mower Deck is Plugged

If grass and other particles accumulate on the mower’s deck, the engine may work harder than necessary. The engine has to work harder to rotate the blades through the debris. Adding blunt blades to an already crowded deck just makes everything worse.

Cub Cadet lawn mower

The deck must be clean of compacted dirt, grass, and other debris. Get those mower blades back in shape. It’s important to run your mower at max power constantly, avoid cutting damp grass, and frequently scrape the deck. 

14. Choke Malfunction

A choke is utilized to reduce air intake to increase fuel injection while the engine is warming up.

When a push mower starts in a cold environment, the choke is used—a stalled lawnmower results from an operator who forgot to release the choke after the engine started running.

15. Blocked Gas Line or Tank

The gasoline lines can become clogged due to varnish and sticky buildups left behind by old fuel. It is also possible to kink or pinch the fuel hose. Your lawn mower won’t make it without gas.

push mower fuel line

You should examine the fuel line for kinks. Repair or change any lines that have become dry, cracked, or damaged. If a blockage is discovered, disconnect the fuel line from the mower, and spray carb cleaner or compressed air into the fuel line.

When Do You Need To Seek Help From a Professional?

Tools You Need and How it Solves the Problem

Sockets and ratchet

Use a socket wrench and ratchet to take the mower’s entire carburetor off. A well-rounded, adaptable toolkit is worth an investment.

Gas and oil siphon

It is an excellent helper for draining gas and excess oil from engines. These chemicals are notoriously difficult to handle without making a mess. Using the siphon eliminates the need to remove oil drain bungs; you can pull the oil out of the dipstick hole instead.

Carburetor cleaner

It does a decent job of clearing up a dirty carburetor; thus, it comes with our highest recommendation. Aerosol can be with directed straw for precise application. It has been developed specifically for carburetor parts to dissolve gum and varnish buildup.

Fuel treatment

Anyone who operates a small engine should invest in gas treatment. You already know that leaving gas in a small engine can lead to serious difficulties, yet most people are unaware that gas expires.

Toro Lawn Mower fuel tank

You can preserve the mower gas for up to two years with the help of a gas stabilizer.

How To Clean the Carburetor

Evaporated gas can gum up the pores of your carburetor and cause it to become blocked. If you leave gas in the tank, it will evaporate over time. The condensed gas might clog the carburetor and render it useless if it is allowed to evaporate inside.

Having the carburetor cleaned and adjusted should get your mower operating smoothly again.

Tools Needed

Step 1: Check the Air Filter

Inspect the air filter regularly. Clean the filter, and the carburetor should function normally again. Black smoke from the tailpipe is a common sign of clogging.

dirty lawn mower air filter

Step 2: Inspect the Connections

If it turns out not to be the filter, you should go to the connections. When unclean, the connections between the throttle plate and the choke plate can become stuck. Vibration might also cause the screws to wear out over time. You may need to get a new carb if the screws are too stripped.

Step 3: Clean the Carburetor

Removing the carb and giving it a deep clean may be necessary if the connectors aren’t the issue. You can remove the carburetor from its mounting bolts by removing the choke and throttle connections from the lever.

There may be screws that need unscrewing if you want to disassemble the carburetor completely.

Get rid of the metering plate and gasket, then detach the primer from the bottom. Your carburetor cleaning solution can remove any lingering residue from the ports now that the internal components have been exposed. 

cleaning lawn mower carburetor

If you want to be thorough, you can use a soft towel to wipe it down afterward.

Step 4: Inspect the Fuel Bowl

Inspect the carburetor bowl. Small amounts of fuel are stored in a reservoir within the fuel bowl and periodically pumped into the engine. Stale gas will accumulate in the fuel bowl and dissipate. Typically, you may find the gas tank behind the air filter.

How Do You Clean the Gas Bowl?

In most cases, a single bolt is required to secure a gasoline bowl in place, but in some cases, that bolt also serves an integral function in the fuel delivery system.

If the gas has been sitting for more than three months, it is no longer usable, regardless of how clean the bowl is. You should get some new gas and refill the tank and carb bowl.

If refilling with fresh gas doesn’t work, follow these steps:

lawn mower gas bowl

Step 5: Wipe Off Any Rust

You could also discover rust inside the carburetor. The time has come to get rid of this rust. Sandpaper can do the trick for getting rid of rust.

Step 6: Put Brack the Carburetor

The carburetor can be reattached after its parts have been cleaned and polished. Before reattaching it to the engine, double-check that the primer, diaphragms, metering plates, and gaskets are all secure.

Still, if something is wrong, you may have the same issue of the engine sputtering to life and dying.

Step 7: Reinstall The Parts and Turn on Your Lawn Mower

Set up the fuel line and the air filter housing back on once you’ve reattached the carburetor. When you’ve finished reassembling your lawnmower, fill it with gas and give it a spin to check if the problem has been resolved.

Husqvarna lawn mower

Double-check all the connections if your lawnmower still has trouble after fixing the faulty carburetor. If the problem persists, a new carb might be the solution.

Using Spray Cleaner To Clean the Carburetor

A spray form of the cleaner is also available. With the carburetor still in place, you can give the aerosol spray cleaning a shot to see if that helps fix the issue.

Make sure the lawnmower’s motor has cooled down before you begin cleaning. Then remove the machine’s air filter cover, the filter itself, and the carburetor’s exterior cover. Keep these pieces separate until the carburetor is completely dry.

Once the carburetor has dried, you can restart the vehicle. There will be a window into the inner workings of the carburetor so you can observe the mechanisms at work. Don’t stop spraying until the area looks clean.

How To Prevent a Lawn Mower Carburetor From Clogging

Taking the carburetor apart and cleaning it regularly is the most effective way to prevent it from getting blocked. 

Walbro Mower Carburetor

To keep your mower running smoothly, you should clean the carb every few uses or after storing it for a while. Investing in a high-quality mower is another way to avoid blockages.

What Does Mower Tune-up Mean?

To extend the lifespan of your mower, regular maintenance is essential. You should get the engine checked at a lawn mower repair shop at least once a season, preferably in the spring. 

The tune-up package of a small engine mechanic includes engine oil, spark plug, air filter, fuel filter, and blade.

Maintenance Tips to Prevent Lawn Mower Problems

Preventative maintenance is the greatest approach to ensure your mower starts up and runs smoothly every time. We recommend doing the following tips:

lawn mower on the ground

Conclusion

If your lawn mower starts then dies, you might have a dirty carburetor, too much oil, defective parts, or any of the reasons we listed above. With a little patience, some tools, a carburetor cleaning solution, and our tips, you will surely have your lawnmower up and running in no time.

Robert Johnson is a woodworker who takes joy in sharing his passion for creating to the rest of the world. His brainchild, Sawinery, allowed him to do so as well as connect with other craftsmen. He has since built an enviable workshop for himself and an equally impressive online accomplishment: an extensive resource site serving old timers and novices alike.
Robert Johnson
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