You’re mowing the lawn and suddenly it begins to sputter and die. To help you quickly identify the problem and get your mower running again I’ve put together a detailed list of causes and repairs.
A Kubota zero-turn starts and then dies when the fuel system is restricted due to old gas, a plugged fuel filter, a clogged fuel line, a faulty fuel pump, a dirty carburetor, or a plugged gas cap.
It may also die from a dirty spark plug, bad ignition coil, plugged air filter, wrong choke setting, plugged cooling fins, wrong engine oil level, or a plugged mower deck.
Follow the safety precautions found in your Kubota operator’s manual. Remove the ignition key and spark plug wires before performing repairs.
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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.
Reasons a Kubota Zero Turn Starts, Stalls, and Dies
1. Bad or Old Fuel
When you begin having problems with your mower and it begins running sluggishly and dies, old fuel is often the underlying problem. This is because gas can begin to break down and become less effective as soon as a month after purchase.
Ethanol, used in most gas today, attracts moisture to the fuel system. Over time, this ethanol and water mixture will separate from the gas and sink to the bottom of the fuel tank. This mixture runs extremely hot through the engine.
Not only is the ethanol and water corrosive, but it also leaves behind varnish and gummy deposits that stick to fuel components restricting fuel flow. The lack of fuel can cause the engine to lose power and die.
When this happens, your Kubota zero-turn may experience a fuel restriction that causes it to run sluggishly and die.
SOLUTION: Check the fuel in the tank. If it has been in the fuel tank for more than 30 days, you need to drain the fuel tank.
Only run fresh gas in the mower. Kubota zero-turns require unleaded gasoline with a minimum 87 octane rating and maximum ethanol content of 10%. Read more about choosing gas for your Kubota mower here.
Before adding gas to the fuel tank, mix it with a fuel additive like Sea Foam Motor Treatment to keep it stable, reduce moisture, and clean the fuel system.
Read Use Sea Foam Fuel Additive in a Lawn Mower to Stabilize Gas to find out more about its advantages.
Once the gas and additive have been mixed, add them to the gas tank. Start the zero-turn and allow it to run for about 15 minutes to work the mixture through the system.
2. Plugged Fuel Filter
You will find a plastic inline fuel filter installed on your Kubota zero-turn. This filter is used to strain fuel coming out of the fuel tank to keep dirt and other contaminants from entering the fuel system.
When the fuel filter becomes plugged with dirt because it isn’t changed out regularly, the engine may die.
SOLUTION: Replace a plugged fuel filter with a new one. When installing the filter, make sure the arrow shown on the side of the filter housing is pointed in the direction of the fuel flow.
3. Clogged Fuel Lines
An effect of running old fuel is a clog in the file line. The gummy substance can build up in the line narrowing the fuel passageway.
Your Kubota zero-turn may die when it isn’t able to get sufficient fuel due to a fuel line clog.
SOLUTION: Check for blockages in your fuel lines using the fuel shut-off valve to start and stop fuel flow while checking each section of the fuel line for fuel flow.
If you find a fuel line that has a blockage, turn off the fuel supply and remove the line from the zero-turn.
Spray carburetor cleaner into the fuel line. This is to loosen up the clog. Follow this by blowing compressed air through the line to remove the blockage.
If you are unable to dislodge the blockage to open the fuel line, install a new fuel line of the same length and diameter. Turn your fuel supply on.
4. Faulty Fuel Pump
A vacuum pump is used on most Kubota zero-turns. It uses the vacuum off the engine to pull fuel from the fuel tank and move it to the carburetor. A fuel pump can fail or degrade from running old fuel.
SOLUTION: To determine you have a bad fuel pump, confirm you are getting fuel flow to the fuel pump by checking flow through the fuel line. You may have done this in the prior step.
Next, check the fuel flow out from the fuel pump. Turn off your fuel flow and remove the fuel line from the carburetor. With the line placed in a container, turn on your fuel flow and start your zero-turn.
Watch for a steady or pulsating flow of fuel out of the line indicating your pump is working. If you don’t get a good flow, replace the fuel pump.
5. Dirty Carburetor
The carburetor regulates the amount of gas and air that mix for combustion to keep the engine running. The carburetor can fail to function right often due to the effects of old gas.
The varnish left behind by old gas can plug fuel passageways and cause the small internal parts to stick. Your Kubota engine won’t receive the right amount of gas to keep running.
Before you disassemble and clean your carburetor perform these simple checks to determine the problem is in your carburetor:
- Confirm you have fuel flow to the carburetor. You should have verified this if you check the fuel flow out of your fuel pump.
- Remove your air filter from the air filter housing.
- Spray carburetor cleaner into the air intake and start your mower.
- If the Kubota starts, runs fine, and then begins to bog down and shuts off, the problem may be in the carburetor.
SOLUTION: Remove the carburetor from your Kubota zero-turn. Disassemble it and clean the carburetor. Refer to this article to clean your carburetor for cleaning steps.
Bring your mower to a small engine repair shop if you choose to have someone else tackle this job for you.
6. Plugged Air Filter
The air filter is an essential maintenance part used to protect the engine from dirt contamination. It keeps dirt and debris from entering the air intake and wearing on the engine.
When your Kubota zero-turn doesn’t get enough air because the air filter becomes plugged, the engine will be starved of air. It may overheat and shut down.
Because of this, you need to make sure the air filter is always in good condition. I recommend replacing the air filter once a year and cleaning it several times during the mowing season.
You will need to do this more often when you use the mower more than the average homeowner or in very dusty condtions.
Follow these instructions to clean a Kubota zero-turn paper air filter:
- Remove your paper air filter element from the air filter housing. Be careful not to allow dirt to fall into the air intake.
- Wipe out any dirt remaining in the housing with a clean dry cloth.
- Tap the filter against a hard surface to knock out as much dirt as you can get to fall out of the filter. Don’t use compressed air as this can damage the paper element.
- Hold your filter up to a light source. Replace your filter with a new one if the light is not shining through the paper element, it is damaged or covered in oil. If you can see light and it is in good condition go ahead and reuse it.
- Install your air filter and reattach the filter housing cover.
7. Plugged Engine Cooling Fins
The engine on a Kubota can overheat after it has been running awhile causing your mower to die. One of the items that can cause overheating is plugged engine cooling fins.
The fins need to be kept clean and free of debris so they can push air around the engine block and cylinder head to keep it cool.
SOLUTION: Remove any dirt you find on your cooling fins and replace any broken fins. Remove dirt from around the engine block and around your engine shroud.
Make sure your heat shield is correctly installed to help with air circulation.
8. Low Engine Oil Level
It’s important to check the engine oil level in your Kubota zero-turn before each use. Many mower owners skip this step. Checking the engine oil level using the oil dipstick is a fairly quick process.
Finding a low engine level before it causes engine damage can save you from a costly repair expense. Running your zero-turn with a low engine level can cause your mower to overheat and shut down.
When there isn’t enough engine oil to lubricate the internal engine components, friction among the parts will build creating heat in the crankcase. This excessive heat can begin burning oil and parts in your engine.
SOLUTION: When you run into a problem with your mower shutting down due to a low engine oil level, you can attempt to add more oil to correct the level and start your mower.
Most of the time, because the Kubota shut down due to a lack of lubrication, this simple fix of adding more engine oil isn’t going to work.
Most likely, significant engine damage was caused. It is best to have an experienced small engine mechanic take a look at your mower to find out how much damage occurred.
A good place to have the engine looked at is at your local Kubota service center or an engine dealer service center for the engine powering your zero-turn. This may be Kawasaki, Kohler, or another engine manufacturer.
9. Too Much Engine Oil
Not only can low engine oil cause the engine to die, but also too much engine oil can make your zero-turn shut down.
Excess oil will cause pressure to build in the crankcase. Read more about the effects of running too much oil here.
SOLUTION: If you find, after checking your engine oil, that your level is too high, remove a little bit of oil.
Oil can be removed from the drain plug, oil filter, or from the oil fill area using an oil evacuator or turkey baster. Continue to remove and add engine oil until the level is corrected.
10. Dirty Spark Plug or Loose Connections
A fouled spark plug can cause your Kubota zero-turn to die. Check your mower for a spark plug that is dirty or damaged.
You’ll also need to make sure the electrode gap matches the specifications required by the manufacturer. Loose spark plug wires can also cause your mower to run sluggish or dies.
SOLUTION: Remove your spark plug and clean the spark plug if it is dirty. If it happens to be very dark in color or damaged, install a new spark plug.
Make sure it is correctly gapped according to your engine manufacturer’s specification and the spark plug wires are securely attached.
11. Bad Ignition Coil
The winding on the ignition coil can separate and short out when your mower is hot. When this happens, the spark plugs are unable to get the voltage they need to create a spark.
This can cause your mower to die after it’s been running for a while.
SOLUTION: Identify a bad ignition coil using an ohmmeter to check for a break in continuity. Replace the ignition coil if you find there is a break.
12. Choke is in the Wrong Position
Your Kubota zero-turn uses the choke to allow a higher concentration of fuel to be allowed into the combustion chamber by restricting the amount of air allowed into the carburetor.
This is needed to start your engine when it is cold. If you leave your choke on after your engine heats up, your zero-turn will die because the engine needs more air to keep it running.
SOLUTION: Make sure your choke lever is in the correct position. The choke must be in the on/closed position to start a cold engine and then adjusted to the off/open position once the engine warms.
13. Bad Gas Cap
The gas cap is designed to allow air to pass through the cap. This is to allow the fuel tank to vent. When the vent in the cap no longer works, the fuel tank will form a vacuum not allowing gas to flow out of the tank.
Your Kubota zero-turn may have started with a bad gas cap, but it will shut down once it has run for a while. This is because a vacuum will form in the tank when air isn’t able to pass through the cap.
SOLUTION: To determine if your fuel cap is bad, loosen the cap to allow air into the fuel tank and see if the mower’s engine runs better.
If it does, tighten the cap and see if you can replicate the problem by running the mower for a while to see if it begins to once again run sluggishly or shut down.
Replace a bad gas cap.
14. Plugged Mower Deck
A plugged mower deck can make your engine work hard, overheat, and shut down.
When grass collects under your mower deck, extra strain is put on the engine when it must turn the blades through a deck full of debris. Dull mower blades can further magnify the problem.
SOLUTION: Regularly scrape the mower deck and sharpen the mower blades. Not only will keeping the mower deck clean and the blades sharp reduce the amount of load on the engine, but it will also provide you with a nice cut.
The deck uses the blades and area under the deck to create air movement to lift and cut your grass.
Why is My Kubota Zero Turn Lawn Mower Battery Not Charging?
Make sure you are running your zero-turn at a high engine speed. Don’t allow your mower to idle for long periods of time. It requires the power of the engine to charge your battery.
Check out 5 Things That Are Draining Your Battery for a list of items that can cause a dead battery.
If you continually have to charge your battery and have confirmed the battery and wiring are in good condition and securely attached, you may have a problem with the charging system.
Solution: There are some steps you can take to check the condition of your battery and charging system which I explain in this article. If after performing these tests, you find you have a bad battery, replace your battery.
When you find the charging system isn’t working right, I highly recommend having an experienced mechanic diagnose and repair the problem.
There are so many components that can cause the charging system to fail that, unless you know the charging system, parts can be thrown at it hoping it repairs the issue.
Electrical components can get expensive and they most likely can’t be returned because they are electrical parts.