13 Kubota Zero Turn Problems (Troubleshoot) (2024)

When you own a Kubota zero-turn long enough, you’re bound to run into problems that need to be addressed before they develop into more serious problems. This is true of all mechanical products as mechanical items wear over time.

Keeping the mower clean and storing it in a dry location helps prevent corrosion from developing on the mower. Performing routine maintenance and using fresh gasoline will help reduce potential problems and extend the life of your Kubota zero-turn.

I have put together a list to help you troubleshoot and narrow down the cause of your mower problem. T These charts and links to articles will help address problems with Z121, Z231, Z421, Z422, Z726, Z781 an other zero turn models.

Follow the safety precautions listed in your Kubota operator’s manual to minimize injury while performing repairs. Always part your mower on a flat level surface, remove the ignition key, and remove the spark plug wire prior to performing repairs.

13 Kubota Zero Turn Problems (Troubleshoot) (1)

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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.

Table of Contents hide

Problem 1: Mower Won’t Start

Problem 2: Mower Starts then Dies

Problem 3: Mower Won’t Move Forward or Reverse

Problem 1: Mower Won’t Start

A Kubota zero-turn won’t start when the engine doesn’t get the air, fuel, and spark required to form an explosion to start. The battery, starter solenoid, and switches can also fail and cause a starting problem.

For More Information Check Out:
Reasons a Kubota Zero Turn Mower Won’t Start

Potential Cause	Solution
Empty fuel tank	Fill with fresh fuel.
Old fuel	Empty the fuel tank. Fill with fresh fuel and an additive to clean the fuel system like Sea Foam.
Bad spark plug	Replace a dirty or damaged spark plug.
Plugged air filter	Clean a dirty air filter. Replace a very dirty or damaged filter.
Plugged fuel filter	Replace the fuel filter.
Clogged fuel line	Remove and clean a clogged fuel line. Replace the line if needed.
Bad fuel pump	Replace a bad fuel pump.
Dirty carburetor	Remove and clean the carburetor. Rebuild or replace if damaged.
Bad battery, loose cables, or corroded terminals	Charge a weak battery. Replace a bad battery that won’t hold a charge. Secure cables and remove corrosion from components.
Bad safety switch	Replace a bad safety switch.
Bad ignition switch	Replace a bad ignition switch.
Bad starter solenoid	Test and replace a bad starter solenoid.

Problem 2: Mower Starts then Dies

Many of the items that cause a zero turn to not start are also reasons a mower will die after running. In addition to these items, you’ll also need to check for a plugged mower deck, bad ignition coil, and low or high engine oil level.

For More Information Check Out:
Reasons a Kubota Zero Turn Starts Then Dies

Potential Cause	Solution
Old fuel	Drain the fuel tank. Mix fresh fuel with a fuel additive to stabilize gas, reduce moisture and clean the fuel system. Add to the fuel tank.
Plugged air filter	Clean a dirty air filter. Install a new filter when it is very dirty or damaged.
Dirty cooling fins	Clean around the cooling fins and replace damaged fins.
Clogged fuel line	Remove a clogged fuel line and attempt to remove the clog. Install a new fuel line when you can’t remove the restriction.
Bad fuel pump	Replace a bad fuel pump.
Dirty carburetor	Remove and clean a dirty carburetor. Rebuild or replace the carburetor when it can’t be sufficiently cleaned or internal parts are damaged.
Bad fuel cap / fuel tank vent	Replace a fuel cap that no longer allows the fuel tank to vent through the cap.
Wrong engine oil level	Correct the engine oil level by adding or removing a little oil until it is at the level recommended by the engine manufacturer. Consult a mechanic when this doesn’t solve the problem. The Kubota may have extensive engine damage.
Plugged mower deck	Scrape the mower deck. Sharpen the mower blades.
Bad ignition coil	Replace an ignition coil that has a break in continuity.
Dirty spark plug	Install new spark plug(s) when they are dark in color, damaged, or worn. Clean them with a wire brush when they are in good condition and slightly dirty.

Problem 3: Mower Won’t Move Forward or Reverse

The hydrostatic transmission pumps fluid to move the wheels. The pressure is so great that you will not be able to free-roll the zero turn without bypassing the transmission.

Make sure the transmission levers are not bypassing the transmission. Check the belt, pulleys, and tensioners to make sure they are securely in place and not damaged. Ensure the oil is fresh and at the full level.

For More Information Check Out:
Kubota Zero Turn Won’t Move Forward or Reverse

Potential Cause	Solution
Transmission bypass levers in the wrong position	Place the transmission bypass levers in the operating position. You will find a lever near each drive wheel.
Drive pump belt is worn	Replace a worn belt and confirm it is sitting securely around the pulleys.
Bad tensioner pulley	Replace the tensioner pulley. Grease the tensioner arm.
Missing or damaged idler arm spring	Replace a broken or missing spring.
Low or old hydraulic oil	Change your hydraulic oil at regular intervals as recommended by Kubota. Check your hydraulic oil periodically to ensure your hydraulic fluid is full. (Note: some transmissions are unserviceable. Consult the Kubota dealer for help)

Problem 4: Mower Vibrates

Even if you have a seat suspension system, you still bounce around when mowing the lawn. When you develop a vibration, the shaking and bouncing can get worse.

Check for worn engine mounting bolts or a bad clutch. Inspect all of the linkages and remove all debris from the mower. Items on the mower deck can fail or wear causing pulleys and blades to wobble and the deck belt to become loose.

For More Information Check Out:
Reasons Your Kubota Mower is Vibrating

Loose or missing engine mounting bolts	Secure the engine mount bolts. Replace any worn or missing bolts.
Failing clutch	Replace a bad electric clutch. Replace a worn clutch cable, lever, or bushings on a manual engagement clutch.
Unbalanced or damaged mower blades	Replaced damaged blades. Make sure they are correctly balanced.
Foreign material wrapped around the blade shaft	Remove foreign objects wrapped around the blade shaft. Inspect the spindle and housing for damage.
Bad spindle housing bearings	Check the spindle bearings and replace them when worn.
Bad deck belt	Replace a worn or loose deck belt.
Bad pulleys	Replace damaged pulleys or pulleys where you feel restriction when turning by hand or a wobble due to a bad bearing.
Debris lodged in the mower	Clean the mower checking all crevices for debris.

Problem 5: Mower Overheats

Engine oil plays an important part in keeping the engine cool. Use an air-cooled engine oil of the right viscosity that is high in zinc. Keep the engine oil level full.

Check for items that can block airflow around the engine including the cooling fins, engine shroud, and engine guard.

Inspect the air filter, mower deck, and mower blade condition.

For More Information Check Out:
Your Kubota Lawn Mower Engine Overheats

Potential Cause	Solution
Wrong engine oil	Drain the engine oil and fill it with fresh oil. Use a 10W-30 oil in most conditions. You may have to use a different viscosity in very warm conditions.
Low engine oil level	Drain the fuel tank. Refill with a fresh gas with an additive to clean the fuel system and stabilize the fuel.
Plugged engine cooling fins	Remove the carburetor and clean it to remove deposits that m
MIssing engine guard	Replace a missing engine guard. Securely attach a loose guard.
Plugged air filter	Replace a dirty air filter.
Plugged mower deck	Scrape the mower deck to remove grass clippings and debris.
Dull mower blades	Sharpen dull mower blades. Replace worn blades.
Overworking the engine	Slow down the ground speed to match the mowing conditions. Avoid cutting wet grass. Double or triple-cut an overgrown lawn.

Problem 6: Mower is Smoking

A Kubota zero-turn smokes when the air filter is plugged, the engine oil is not correct, or a bad engine gasket has caused oil to seep onto a hot surface like the muffler.

When you can’t find the cause of the smoke, you may have internal engine issues like a worn piston ring or a burnt valve. In this case, I recommend having a small engine technician perform tests to determine the cause.

For More Information Check Out:
Why Your Kubota Lawn Mower is Smoking

Potential Cause	Solution
Plugged air filter	Replace a plugged air filter.
Too much engine oil	Remove a little engine oil from the crankcase until it is corrected. Check the condition of the air filter.
Low engine oil level	Have a small engine technician inspect the engine. You can correct the engine oil level, but chances are the engine is damaged if it began smoking due to low engine oil.
Bad engine gasket	Locate the bad engine gasket and repair it.
Internal problems: piston ring or valve train	If you continue to experience engine smoking, a small engine technician must perform testing to determine the cause of internal engine damage.

Problem 7: Mower Has a Weak Hydrostatic Transmission

Hydrostatic transmissions on a Kubota zero-turn may experience a weak transmission when the hydraulic oil is old or the hydraulic tank is low on oil.

It can also feel weak when the drive belt or tensioner pulley is worn or broken.

Potential Causes	Solutions
Bad drive belt	Replace a worn pump drive belt
Bad tensioner pulley	Replace a bad tensioner pulley. Grease the tensioner arm.
Low or old hydraulic oil	Change the hydraulic oil at regular intervals. Keep the hydraulic oil level at the full level.

Problem 8: Mower Won’t Drive Straight or Steer Correctly

When a zero turn doesn’t drive straight and pulls to one side, check the tire pressures and dampers. If these items are in good condition, you may just need to track the mower so each tire rotates at the same speed.

Potential Cause	Solution
Incorrect tire pressure	Ensure the tires are filled to the manufacturer’s specifications. The tire pressures must be equal on each side of the zero-turn.
Bad dampers	Replace with new dampers.
Tracking adjustment needed	Adjust the speed adjustment bolt to change the rotation speed of the tire so each tire moves at the same speed. Refer to your owner’s manual.

Problem 9: Mower is Running Rough and Sputters

When you find your Kubota zero-turn is running rough and bogs down, look for items that can restrict fuel flow or airflow or can cause an intermittent spark.

You’ll also need to look at items that can put extra load on the engine like a fast ground speed, plugged mower deck, and dull mower blades. Not having your throttle at its fastest speed can also cause the engine to run sluggishly when the blades are engaged.

For More Information Check Out:
Kubota Lawn Mower is Running Rough or Sputtering

Potential Cause	Solution
Old fuel	Drain old fuel. Refill with a gas and fuel stabilizer mixture.
Clogged fuel line	Remove a clogged fuel line and remove the clog using carburetor cleaner and compressed air. Install a new fuel line when the clog can’t be removed.
Plugged fuel filter	Replace the fuel filter.
Dirty carburetor	Remove the carburetor to clean it. Rebuild or replace it if needed.
Bad gas cap	Replace a gas cap that no longer allows the fuel tank to vent.
Dirty spark plug	Clean a dirty plug using a wire brush. Install a new one if it is very dark in color, worn, or damaged.
Fast ground speed	Slow down the ground speed to match the mowing conditions. Slow down when mowing tall, thick, or wet grass so the engine isn’t under too much load.
Low engine speed	Place the throttle lever in its highest position when engaging the mower blades.
Plugged mower deck	Scrape the mower deck to keep it clean.
Dull mower blades	Sharpen the mower blades.

Problem 10: Mower Blades Won’t Engage

The mower blades won’t engage on a Kubota zero turn when the PTO switch is faulty, the battery is weak, a safety switch failed or the clutch is bad.

The blades won’t turn when the belt is worn or has fallen off the pulleys due to a stretched belt, bad pulley bearing, or worn tensioner parts.

For More Information Check Out:
Kubota Mower Blades Won’t Engage or Turn On

Potential Cause	Solution
Worn mower deck belt	Replace a belt that is worn, cracked, or has a shiny glazed appearance.
Belt falls off the pulleys	Replace worn or damaged deck parts including a worn idler arm, worn spring, or bad pulleys. Replace a stretch mower deck belt.
Bad PTO switch	Replace the PTO switch.
Bad clutch	Replace the clutch. On a manual engagement clutch, replace a worn clutch cable, lever, springs, and linkages.
Weak battery	Test the battery and place it on a charger if the reading is less than 12.7 volts for a 12-volt battery. Replace the battery when it won’t hold a charge.
Bad Safety switch	Replace the safety switch
Blown fuse	Replace the fuse with the same capacity fuse.

Problem 11: Mower is Leaking Gas

It can be difficult to find where a Kubota is leaking gas especially if the gas has evaporated into the air and doesn’t leave any wet spots behind.

Common areas to check for a leak is the carburetor and dry cracked fuel lines. You may also develop fuel leaks from fuel components from plastic components that degrade or seals that dry out.

For More Information Check Out:
Reasons Your Kubota Lawn Mower is Leaking Gas

Potential Cause	Solution
Bad carburetor bowl gasket	Replace the gasket located between the carburetor bowl and the carburetor.
Stuck carburetor float or float needle	Clean the carburetor and replace any damaged parts.
Cracked fuel line	Replace the fuel line.
Bad fuel tank	Replace a fuel tank that begins leaking at the seams
Bad fuel shut-off valve	Replace the fuel shut-off valve
Weak fuel filter	Install a new fuel filter.
Bad fuel pump	Install a new fuel pump.
Bad gas cap seal	Replace the gas cap. You may be able to purchase only the rubber seal on some caps.

Problem 12: Mower Clicks & Won’t Turn Over

When the Kubota zero-turn just clicks when you go to start it, you may have a bad starter solenoid. In addition to the solenoid, check the items that can affect the power getting to the solenoid.

These include the battery, cables, terminals, and ground. When the fault doesn’t lie with any of these items, check the starter motor.

For More Information Check Out:

Potential Cause	Solution
Damaged or loose battery cables & wiring	Replace damaged cables. Remove any corrosion on the terminals or other components. Secure loose cables.
Weak or bad battery	Test the battery and place it on a charger if the reading is less than 12.7 volts for a 12-volt battery. Replace the battery when it won’t hold a charge.
Bad ground	Remove corrosion from the ground. Make sure the ground cable from the battery and ground cable from the starter solenoid is making good contact. (A 3-post solenoid is self-grounded)
Faulty starter solenoid	Test the starter solenoid and replace it if faulty.
Bad starter motor	Replace a bad starter motor.

Problem 13: Mower Has a Bad or Uneven Cut

There are many items that can affect the cut quality of your Kubota zero turn. First, check the tire pressures to make sure you don’t have a low tire that is causing the deck to sit unleveled.

Next, at the condition of the components on the top of your mower deck and underneath the deck. Sharpen dull blades, replace components with bad bearings and replace a worn deck belt.

For More Information Check Out:
Reasons for a Kubota Zero Turn Bad or Uneven Cut

Potential Cause	Solution
Dull or worn mower blades	Sharpen the mower blades. Replace blades that are extremely worn where the blade sails are thinner than the center of the blade or the blade ends are worn and rounding.
Bent mower blade	Replace a bent mower blade.
Blade installed wrong	Make sure the blades are installed with the correct hardware. The blade sails must be pointed upward toward the mower deck.
Bent blade spindle	Replace a bent spindle. Inspect the spindle housing for damage.
Bad mower deck belt or bad pulleys	Replace a deck belt that is stretched, worn, cracked, or has a glazed appearance. Slowly rotate the pulleys by hand. Replace the pulleys when you feel a restriction, hear a bearing noise, or the pulley is wobbling.
Mower deck is plugged with grass clippings & debris	Scrape the mower deck.
Uneven tire pressure	Correct the tire pressures. Make sure they are even on the left and right-hand sides.
Unleveled mower deck	Level the mower deck so the mower deck is level side-to-side. The mower deck sits slightly lower in the front than in the rear. Consult the operator’s manual for exact specifications to level the deck.
Engine speed is too low	When engaging the blades, have the throttle set at the highest level.
Ground speed is too fast	Slow down when mowing thick, wet or tall grass. Mowing in these conditions puts extra strain on the engine. Running the mower too fast can end up pushing over some grass instead of cutting it.
Operator error	Properly overlap paths so strips of grass are not left in between passes. Use a small format deck like a push mower to mow ditches and other steep changes in grade.