With so many things that can prevent your riding lawn mower from starting, it’s hard to know exactly where to start and what you need to check. I’ve put together this list to help you troubleshoot your starting problem.
A riding mower won’t start when it isn’t getting sufficient air, fuel, and spark.
This may be due to a dirty air filter, bad spark plug, plugged fuel filter, clogged fuel line, bad fuel pump, dirty carburetor, weak battery, faulty starter solenoid, or bad ignition switch.
Keep reading for additional items that can cause your starting issue. Always remove the ignition key and spark plug wires prior to performing any work on your mower.
This post may include affiliate links. Purchases made through these links may provide a commission for us, at no extra cost to you. As an Amazon Associate, we earn from qualifying purchases.
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.
Troubleshoot a Mower Starting Problem: Fuel, Air, and Spark
An internal combustion engine on a mower requires fuel and air to be introduced to the cylinder. This mixture is compressed and ignited with spark to form combustion.
Before beginning to check for starting problems verify these 4 things:
- The fuel shut-off valve is open allowing fuel to flow out of the fuel tank.
- There is sufficient fresh fuel in the fuel tank.
- The parking brake is engaged or the bail lever is engaged.
- The PTO switch is off (riding mower, lawn tractor, and zero turn).
- The choke is in the closed / on position to start a cold engine.
Check for a Fuel Problem
Old gas is often the root cause for fuel-related issues resulting in components not functioning or clogs developing.
Before checking for a fuel problem, if your mower has a fuel shut-off valve, make sure it is in the open position. This valve is often moved to the closed position when the mower is stored or for transportation.
Perform this test to narrow down your problem to the fuel system:
- Detach the air filter cover and remove the air filter.
- Spray carburetor cleaner into the air intake. Find out why I use carburetor cleaner and not starter fluid.
- Attempt to start your mower.
- If the mower attempts to start or starts, then you have a problem with the fuel system.
- The most common fuel issues are a dirty carburetor, clogged fuel filter, and clogged fuel lines. The fuel pump may also be an issue if your mower uses one.
- If the mower doesn’t attempt to start, you most likely have a spark plug problem.
- If the mower attempts to start or starts, then you have a problem with the fuel system.
Check for an Airflow Problem
Air is an important component needed for your engine to start. The engine must run rich to start a cold engine. This condition allows more fuel and less air into the cylinder.
Airflow is controlled by the choke. You will find a choke lever that opens the choke plate to introduce more air and close the choke plate to restrict air.
Perform this test to narrow down your problem to the air supply system:
- Detach the air filter cover and remove the air filter.
- Inspect the air filter’s condition. A clogged air filter will restrict airflow. Clean the filter or replace it if it is very dirty or damaged.
- With the air filter removed, inspect the choke plate.
- Move the choke lever to the on position: The choke plate should be closed.
- Move the choke lever to the off position (on some models, this is placing the throttle in the fast throttle position): The choke plate should be open.
- If the choke isn’t opening and closing correction, check the choke linkage and choke cable. Loosen a stuck choke by lubricating the linkages and choke shaft using carburetor cleaner. Replace a bad choke cable (if used on your model).
Check for a Spark Problem
Spark must be released at the right time for combustion. A spark plug may fail to spark if it is dirty or damaged. It may also fail due to a loose spark plug wire, a bad ignition coil (armature), or other ignition system problems.
Perform this test to narrow down your spark problem:
- Remove the spark plug wire (boot) from the spark plug.
- Attach a spark plug tester to the spark plug ignition wire.
- With the spark plug still installed, attach the other end of the spark plug tester to the spark plug.
- Attempt to start the engine using the pull cord or electric start.
- You will see a glow in the transparent section of the tester if it is generating a spark.
- If you don’t see a glow, the spark plug may be bad or you may have a bad ignition coil. On electric start models, you may have a problem with the ignition system including the battery, wiring, and starter solenoid.
This is Why Your Riding Mower Won’t Start
1. Fuel Tank is Empty
Everyone knows a gas-powered riding lawn mower needs gas to start and run. When you’re in the middle of troubleshooting why your mower won’t start, you can often skip the simple obvious solutions like adding gas to your mower.
FIX: Add fresh fuel to an empty gas tank
2. Wrong or Old Gas
Right Type of Gas
With so many types of fuel on the market today, it can be easy to grab the wrong type of fuel at the gas station.
A riding lawn mower requires unleaded gasoline with a minimum 87 octane rating and an ethanol content of 10 percent or less. This type of gas is often sold as Regular or E10 fuel.
To make sure you’re choosing the right fuel, read the decal on your fuel pump. It will list the octane rating and the ethanol content percentage.
For more information on the type of gas you need to use in your riding mower and why it’s important to select high-quality fuel, check out my article about the right gas to use in a riding mower.
Use Fresh Gasoline
The combustion properties in fuel are best within its first 30 days. The gas then begins to break down and become less effective. The ethanol in gasoline attracts moisture that can cause your riding mower to run rough or not run at all.
Old fuel with ethanol can leave a gummy substance causing fuel blockages and resulting in starting problems with your riding mower.
FIX: Drain and flush the fuel tank. Add fresh fuel that includes a fuel additive to stabilize and clean your fuel system like Sea Foam. Read more about the advantages of using Sea Foam Motor Treatment in your riding lawn mower.
3. Gas Cap Won’t Vent
The gas cap you use on your riding mower must vent allowing air to pass through the cap. Over time, the cap can become clogged. When this happens, a vacuum is formed in your fuel tank that doesn’t allow fuel to flow out of the tank.
You may have experienced this with your favorite travel mug. Your lid will have a small hole for air to pass through.
When something clogs this hole, a vacuum is formed in the mug and it’s hard to get your drink to sufficiently flow out of the mug.
When your gas cap doesn’t vent, your riding mower won’t start because of the lack of fuel in the engine. To troubleshoot this problem, remove your gas cap, start your mower, and let it run.
Be careful to not let any contaminants enter the fuel system with the cap off.
If your mower seems to start and run fine, replace the gas cap and continue to let the mower run for a while. If it begins to bog down and shut off, the fuel cap could be the cause of your starting problem.
FIX: You can try to clean your cap and remove the clog to allow your gas cap to vent. If this doesn’t work, you’ll need to replace your gas cap.
4. Bad Spark Plug or Loose Connection
Your riding lawn mower may use one or two spark plugs. When your spark plug has a loose connection or is not properly gapped, you can have a starting problem.
You will also need to check for a damaged spark plug and for carbon buildup that can cause the spark plug to foul out.
FIX: Remove your spark plug and inspect it for signs of carbon buildup or a cracked porcelain insulator. Replace with a new spark plug(s). Make sure they are correctly gapped and the spark plug wires are secure.
5. Air Filter is Plugged
Your riding lawn mower’s engine requires air to run. When your air filter becomes completely plugged with dirt and debris, your engine will not start because it can’t draw air through the filter.
Extensive engine damage can occur from running an extremely dirty air filter. When the engine can’t get air, it will overheat. It may even draw air and oil out of the crankcase because it’s the only air it can find.
It is essential to check your air filter regularly as this is a layer of protection for your engine. Cleaning and replacing your air filter when needed is a simple task that can prevent significant damage to your riding mower.
FIX: Check your air filter by removing it from the air filter housing and
Remove your air filter from the air filter housing to check for dirt build-up. Tap a paper air filter against a hard surface to remove as much dirt as possible. Don’t use an air compressor to clean your paper element.
Once you have finished removing the dirt, hold your filter up to a light source. If you can see light shine through the paper element, you are good to reuse it. If you cannot, you need to replace it with a new air filter.
6. Fuel Pump is Bad
Most riding mowers use a vacuum fuel pump. This pump can go bad over time and will not be able to use the engine vacuum to draw fuel out of the fuel tank and move it to the carburetor.
Gas running through your fuel pump can degrade the plastic and its internal components. Check for signs of fuel leakage on your pump.
You will need to replace the pump if you find any leaks as this is a sign your pump is no longer sealed and able to work as designed.
If you don’t see signs of leaking, you’ll have to test fuel flow to check for a pump failure that may cause your riding mower not to start.
Using your fuel shut-off valve or clamps on your fuel lines to stop and start fuel flow, you need to check for fuel flow to the pump.
Once you verified you are getting fuel to the pump, check your pump to make sure a steady or pulsating flow of fuel is coming out of the outlet port.
FIX: Replace your riding mower’s fuel pump if you are not receiving a constant or pulsating flow out of the pump.
7. Plugged Fuel Filter
Check your inline fuel filter to verify fuel is passing through your filter. I like to replace mine at the beginning of every season so I can make sure I have an element that is filtering dirt and preventing it from entering my fuel system and mower engine.
FIX: A clogged fuel filter must be replaced with a new one. Fuel filters are one of the least expensive parts you need to purchase when servicing your riding mower.
8. Clogged Fuel Line
Old fuel can cause clogging in your fuel system which includes your fuel lines. You won’t be able to visibly see the clogs.
So, if your riding mower will not start because it is not getting fuel, you’ll need to check each section of the hose for blockage. You’ll do this by stopping and starting fuel flow using your fuel shut-off valve or clamps.
FIX: Once you find a clogged line, try to remove the blockage by spraying carburetor cleaner into the line to help loosen it. Follow this by blowing compressed air through the line until it is no longer clogged.
If you notice the fuel line is dry and brittle or you are unable to remove the clog, you must replace your fuel line with a new fuel line.
9. Clogged & Dirty Mower Carburetor
Your carburetor can become dirty and gummed up making the components in your carburetor no longer able to function as designed.
The carburetor’s function is to regulate the mixture of fuel and air needed to create combustion in your engine’s cylinder. When it fails to do this, your riding mower may not start.
FIX: If you are a little mechanical and comfortable with working with small parts, you should be able to handle cleaning your carburetor. You can have your local small engine mechanic clean your mower carburetor if you are uncomfortable with the cleaning process.
Clean your riding mower’s carburetor by taking it apart and using carburetor cleaner to clean the dirt and gummy deposits. You can find steps for cleaning your carburetor here.
If your carburetor is too dirty to clean adequately, you should replace it. When you have parts that have failed, you may need to rebuild your carburetor or replace it with a new one.
10. Bad Battery, Loose Cables, or Corroded Terminals
Your riding mower will not start with a bad battery, loose cables, or corroded terminals. Confirm your battery terminals are not corroded and are attached securely to the battery.
FIX: Clean corroded terminals in a baking soda solution containing 2 cups of water and 3 rounded tablespoons of baking soda. Use a wire brush to scrub the terminals clean.
Test your battery with a multimeter. You need a reading of about 12.7 volts. Place on a charger to charge your battery if your reading is less than this.
Read more about the steps and items needed to charge your battery here. If your riding lawn mower battery does not hold a charge, you will need to replace it with a new battery.
11. Bad Safety Switch
Your riding lawn mower uses safety switches for the operator’s safety. You will have a safety switch that disengages the mower deck when it does not sense the operator is in the seat.
It also has a safety switch that will prevent your riding mower from starting when you don’t have the parking brake engaged.
Your riding mower may have additional safety switches which will be shown in your operator’s manual. When a switch fails, your riding mower may no longer start.
FIX: Test the switch using a multimeter or you can temporarily bypass the safety switch to identify a bad switch. Never operate a riding mower without a working safety switch.
Never run a mower when a safety switch is bypassed. You never know when you will encounter a situation where the safety switch can save you from serious injury.
12. Bad Ignition Switch
When you insert your key into the ignition switch and nothing happens or it just doesn’t feel right when you turn your key, you may have a bad ignition switch preventing your riding mower from starting.
The ignition switch should be tested.
FIX: You can use a multimeter to test the ignition switch. Replace the switch if bad.
13. Bad Starter Solenoid
A lawn mower solenoid is an electromagnetic switch that is like an on-off switch that actuates the starter motor to turn over the engine. A click or hum when turning your ignition key is an indication to check your solenoid.
Another indication your riding mower solenoid may be bad is when a wire attached to your solenoid gets hot and begins to smoke or melt.
FIX: Test the riding mower starter solenoid by following the steps here. Replace your solenoid if it is found to be bad.
Read more about reasons a riding mower engine isn’t turning over.
14. Blown Fuse on Riding Lawn Mower
A fuse is installed to protect your riding lawn mower’s electrical system. Check your mower to make sure you don’t have a blown fuse. The location of the fuse block can vary depending on the manufacturer of your riding mower.
A good place to start is looking around your battery. It may be placed under or next to this area. You may also find your fuse behind your dash.
FIX: Replace your blown fuse. Use a fuse with the same amperage as the fuse you are replacing.
If you continue to blow fuses, you should bring your mower to your local lawn mower repair shop or your local lawn mower dealership to troubleshoot the root cause of the electrical failure.
15. Faulty Lawn Mower Charging System
While the charging system isn’t the main reason your mower won’t run, it can contribute to a weak battery that prevents the mower from starting.
When the charging system fails to charge the battery, the battery may not be able to start the mower the next time you go to use it.
A bad stator or alternator can be the problem, but there are other items that can cause your charging system to fail. I have steps on how to test your charging system using an ohmmeter in this article.
FIX: Have your local mower repair shop check your charging system to isolate the problem. If you don’t have experience with charging systems, you will most likely just be replacing electrical items until you find one that works.
This can get very expensive because most parts stores won’t let you return electrical parts if you find a part you purchased doesn’t resolve your starting problem.
16. Incorrect Starting Procedure
There are special operating procedures that must be followed to start and operate your lawn mower. Some of these are safety procedures while others are controlling the throttle and choke to start the mower.
FIX: Refer to your operator’s manual to ensure you are operating your lawn mower correctly, so you don’t set off the safety features that prevent your mower from starting.
Still Having Problems With Your Riding Mower?
As a lawn mower owner, when you own it long enough, you are going to run into different types of problems. This may include problems where your mower is smoking, cutting unevenly, losing power, not starting, leaking fuel, and more.
Check out this handy guide including charts for common mower problems and solutions:
Common Riding Lawn Mower Problems & Solutions.
If you are unable to fix your mower or don’t want to attempt a more complicated repair, have your local lawn mower dealership or repair shop for assistance.