Kubota makes a zero-turn that competes with the best zero-turns on the market. That doesn’t mean it will never have problems.
A Kubota zero-turn won’t start due to a plugged fuel filter, clogged fuel line, dirty carburetor, bad gas cap, bad spark plug, bad starter solenoid, faulty switch, bad battery, plugged air filter, or wrong choke setting.
Keep reading for additional starting problems. Stay safe by following the safety guidelines in your Kubota operator’s manual. This includes waiting for the engine to cool and removing the spark plug wire(s) 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 Mower Won’t Start
1. Empty Fuel Tank
I only mention checking the fuel tank just in case you forgot this obvious reason and started to check other items on your Kubota zero-turn.
You may have developed a fuel leak, the fuel gauge may be faulty, or you may have simply forgotten the last time you added fuel.
SOLUTION: Check the fuel system to make sure you haven’t developed a fuel leak. If you find a leak or faulty component, repair it or replace it. Add fresh fuel to the fuel tank.
2. Wrong or Old Gas
Correct Gas for a Kubota Zero-Turn Lawn Mower
Using the right fuel and keeping it fresh is essential for the mower to run well. Old gas is often the main culprit when a Kubota zero-turn starts running sluggishly, won’t start, or dies after running.
Ethanol found in most gas today naturally attracts moisture from the air to the fuel system. The ethanol and water mixture can leave behind varnish and gummy deposits.
This causes fuel restrictions or component failures. When your Kubota can’t get a sufficient flow of gas, it may have problems starting.
Because ethanol has negative effects on a zero-turn engine and fuel system, always use gas with low ethanol levels or fuel that is ethanol-free. Gas with high ethanol levels can cause significant engine damage.
Kubota zero-turns require unleaded gas with a minimum 87-octane rating and a maximum of 10% ethanol content. Read more about choosing the best gas for a Kubota zero-turn here.
Only Use Fresh Gasoline in a Kubota Zero Turn
Because gasoline begins to break down and becomes less effective as soon as 30 days, it is important to purchase gas and consume it within this time.
If you purchased more gas than you can consume within 30 days, use a fuel additive like Sea Foam Motor Treatment to stabilize the gas so it lasts a little longer.
I love this product! I add it to all of my small engine fuel as added protection to the fuel system. Read more about its advantages in Use Sea Foam Fuel Additive in a Lawn Mower to Stabilize Fuel.
SOLUTION: When you find you filled the fuel tank with the wrong fuel or the fuel is old, you must drain the fuel tank. A manual siphon pump is an inexpensive tool that works well to drain the tank.
Add fresh gas and a fuel additive to clean the fuel system, reduce moisture, and stabilize the fuel.
3. Plugged Fuel Filter
A Kubota zero-turn uses a fuel filter to strain fuel coming out of the fuel tank to keep dirt and debris from entering the fuel system.
This filter should be replaced once a year to ensure it stays in good condition. If you find a tank of fuel was very dirty, you may have to replace the filter more often.
However, if you realized the fuel was dirty, you shouldn’t use it. You should drain the fuel tank if it is already in the tank.
When the fuel filter isn’t changed out regularly, it can become plugged. It won’t allow sufficient fuel to pass through the filter.
SOLUTION: A clogged fuel filter must be replaced with a new one. Make sure you install it correctly with the arrow on the filter pointed in the direction of the fuel flow.
4. Clogged Fuel Line
The sticky deposits left behind by old fuel can get stuck in the fuel lines. This narrows the opening in the line restricting fuel flow.
SOLUTION: Once you find a clogged line, try to remove the blockage. To do this, remove the line from your Kubota.
Spray carburetor cleaner into the line to try to loosen the blockage. Follow the carb cleaner with compressed air blown into the line to remove the clog.
If you are unable to dislodge the clog, Purchase a new fuel line making sure you get the right diameter and length of the fuel line. You’ll most likely have to cut the amount of line you need.
I do recommend replacing your fuel lines, even if you don’t find a clog in them if your fuel lines are dry and beginning to crack.
5. Bad Fuel Pump
The fuel pump on your zero-turn may be causing it to not start. The function of the fuel pump is to work against gravity and get fuel up to your carburetor.
When it fails, the carburetor doesn’t receive the fuel it needs and the engine is unable to start. A carburetor can fail over time.
Most Kubota zero-turn mowers use a vacuum-style fuel pump. Over time, fuel can cause your fuel pump to degrade. For a pump that is no longer able to use the engine vacuum to draw fuel out of the fuel tank so it gets to the carburetor, the pump must be replaced.
If the fuel pump is leaking fuel, you must replace it. When you can’t see any visible signs of damage to your pump, perform a couple of tests to identify a pump problem:
- Shut off your fuel supply using the fuel shut-off valve under your fuel tank or use clamps to pinch the fuel line to stop the flow.
- Remove the hose from the inlet port on the pump. Place it in a container placed lower than the fuel tank so fuel can flow into the container using gravity. This step is to confirm your fuel pump is getting the fuel.
- Start your fuel flow. If you are getting flow into the container, you have confirmed you are getting fuel flow to the pump. If you are not, you have a fuel restriction you need to locate before the pump.
- Shut off the fuel flow. Replace the hose on the inlet port.
- Remove the hose from the carburetor and place it in a container so you can confirm the condition of your fuel pump.
- Start your fuel flow and start your engine. Watch for a steady or pulsating flow of fuel out of the fuel line.
- Once your test is done shut off your mower and reattach your fuel hose to the carburetor.
SOLUTION: Replace the Kubota fuel pump if you are not receiving a constant or pulsating flow out of the pump.
6. Dirty Carburetor
A dirty carburetor can be the reason your Kubota zero-turn will not start and run. When the carburetor can’t regulate the amount of air and fuel the engine receives the engine will fail to start.
Old fuel often plays a role in a carburetor failure. This is because old fuel clogs the fuel passages restricting fuel flow. It can also leave behind varnish that causes internal parts to stick and no longer function.
When your carburetor does not work properly, you will have to clean the carburetor and replace any stuck or damaged parts that are unable to be cleaned.
SOLUTION: I have listed steps for cleaning your Kubota mower carburetor here. Follow these if you have a little mechanical ability and are comfortable working with small parts.
If you do not what to attempt cleaning or rebuilding your carburetor, you can take your mower to your small engine repair shop to be cleaned or you can replace it with a new carburetor assembly.
7. Bad Gas Cap
The fuel tank must be able to vent allowing air to pass in and out of the tank. When there isn’t a vent, the tank forms a vacuum keeping fuel from leaving the fuel tank and getting to the carburetor.
On a Kubota zero-turn, the tank vents through the fuel cap so the air pressure in the tank is equal to the air pressure outside of the tank.
You may be able to identify a bad gas cap by running your Kubota with and without the cap. If your zero-turn won’t start with the cap in place, loosen the cap to allow air in the fuel tank. You may hear a vacuum release.
If you are able to start the mower after loosening the cap, you may have a gas cap venting problem.
Tighten the cap and run the mower to see if you can recreate the issue where it shuts off and then won’t restart until the fuel cap is loosened.
SOLUTION: Replace a Kubota zero-turn fuel cap.
8. Bad Spark Plug
When your spark plug wires are loose or the gap is set incorrectly, you may have intermittent running or starting issues with your zero-turn. Fouled spark plugs can also cause intermittent spark problems.
Check your spark plug to ensure your starting issue on your zero turn isn’t due to the spark plugs.
SOLUTION: Remove your spark plug and inspect it for signs of carbon buildup or a cracked porcelain insulator. Replace with a new spark plug(s) if they are damaged, worn, or very dark in color.
If the spark plug(s) is in good condition, clean the tip with a small wire brush. Make sure the spark plugs are correctly gapped and the wires are secure.
9. Clogged Air Filter
Using a clean air filter not only allows your engine to get the clean air it requires but also prevents dirt from entering the cylinder and causing significant damage to the engine.
I recommend replacing the air filter annually and checking its condition regularly through the mowing season. If you find the filter is in good condition, clean it. However, if it is very dirty or damaged, it’s best to replace it with a new one.
SOLUTION: Check and clean the air filter. If the air filter is so bad that it’s keeping your Kubota from starting, you should install a new one.
Clean a Kubota paper air filter:
- Remove the air filter from the filter housing.
- Don’t let any dirt fall into the air intake. Wipe out any excess dirt that remains in the filter housing and filter cap with a dry cloth.
- Tap the air filter against a solid surface to knock as much dirt loose as possible and allow it to fall out of the filter.
- Hold the filter up to a light source and check for light shining through the paper element.
- Reuse the filter if you can see light. Replace your filter with a new filter if you cannot see light, it is extremely dirty, or the filter is damaged.
- Install the air filter.
10. Loose Cables or Corroded Terminals, Wiring, or Components
Loose cables and corroded electrical components, wiring, and terminals can cause a zero turn not to start.
SOLUTION: Remove any corrosion you find. To do this, disconnect the battery and remove the corroded components.
Use a baking soda solution (2 cups of water mixed with 3 heaping tablespoons of baking soda) or cola to remove the corrosion along with a small metal brush.
Then, make sure all wiring and components are securely installed making good connections.
11. Weak or Bad Battery
A battery that has a weak charge will not provide enough power to start a Kubota zero-turn. If the battery isn’t able to hold a charge, you need to replace it with a new battery.
SOLUTION: Test your zero-turn battery with a multimeter. If your reading is less than 12.7 volts, place your battery on a battery charger. Read more about the steps and items needed to charge your Kubota battery here.
12. Bad Safety Switch
Your zero turn has an operator presence control system installed to keep you safe. A safety switch can be defective and cause your zero-turn to fail to start.
SOLUTION: Test your switches using a multimeter. You can also temporarily bypass a safety switch to identify a bad switch, but only do this for troubleshooting purposes.
Never operate a mower without the safety switch. Never run a mower when a safety switch is bypassed. A safety switch can save you from serious injury and you never know when you’re going to need it.
13. Bad Ignition Switch
The ignition switch could be the problem when you insert the key and find it fails to start.
SOLUTION: You can use a multimeter to test the ignition switch. Replace the switch if bad.
14. 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 solenoid may be bad is when a wire attached to your solenoid gets hot and begins to smoke or melt.
SOLUTION: Test your Kubota solenoid by following the steps here. Replace your solenoid if it is found to be bad.
15. Faulty Charging System
While the charging system isn’t the main reason a Kubota zero-turn mower won’t start, 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 along with several other electrical parts. Read this article to test your charging system here using an ohmmeter.
SOLUTION: Once you identify the problem that lies in your charging system, my advice to you is to bring it to your local Kubota zero-turn mower dealership for troubleshooting.
There are many components that make up the charging system. Without the experience, you will most likely be throwing parts at your mower hoping to find the problem.
Electric parts on your lawn mower can be expensive. Most likely, electric parts are non-returnable. So, if you find the expensive part you bought is not the problem, you are stuck with it.
16. Incorrect Operating Procedure / Wrong Choke Setting
There are several starting procedures you will need to follow in order to start your zero-turn.
Check the Choke Setting
The choke is used to restrict airflow when starting a cold engine. When the choke lever isn’t in the right position, the mower can fail to start.
- Starting a COLD Kubota zero-turn:
- Place the choke lever in full choke position.
- Place the throttle halfway between slow and fast throttle positions.
- Turn the key to the start position and then release it once the engine starts.
- Adjust the choke lever to the off position.
- Allow the engine to idle at half throttle for a few minutes before adjusting to full throttle to begin mowing.
Ensure you are not setting off the Kubota safety interlock system
The safety interlock system is designed to keep you safe. Your Kubota won’t start if you don’t satisfy the safety requirements required to use the mower.
Check these safety measures are met to start the zero turn:
- Sit in the operator’s seat.
- Confirm the brake is engaged.
- Make sure the PTO is off.
SOLUTION: Follow the steps above to start your Kubota zero-turn. This includes following the safety starting procedures and having the choke in the correct position. For starting procedures specifically for your model mower, consult your operator’s manual.