17 Kubota Zero Turn Mower Problems: Troubleshooting Guide

Kubota is one of the most popular zero turn mower manufacturers. Homeowners and commercial users alike praise these machines for their reliability and long lifespan. Like all vehicles, though, they can develop problems sometimes. If you have a Kubota Z400, Z421, Z700, Z724, Z725, ZG20, ZD21, ZD25, ZD221, ZD331, ZG23, or ZD1511 mower, this zero turn troubleshooting guide is for you. 

The most common Kubota zero turn mower problems include starting difficulties and engine overheating. Causes can vary from an engaged safety switch to a flat battery, problems with the fuel, or electrical problems. Grass cutting issues could also happen due to incorrect operation or improper maintenance.

Check out below the most common problems Kubota zero turn mowers may have and their possible causes.

Kubota zero-turn mower problemPossible cause
Difficult startSeat safety switch locked in the engaged position
Insufficient powerFuel supply problems or clogged nozzle
Engine running roughDefective spark plug, carburetor, or ignition coil
Engine overheatingOverloaded engine or insufficient cooling oil or clogged air intake
Starter motor not functioningFlat battery or poor terminal connections
Weak starterA flat or defective battery
Battery not rechargingDefective battery
Low electrolyte levelCracked electrolytic cells
Rough operationInsufficient transaxle fluid 
Mower doesn't move while the engine is runningEngaged parking brake or insufficient transaxle fluid
Blades don't engageFaulty PTO system
Mower belt slippingWorn or loose belt
Uneven cutUneven deck level or bent blades 
Streaking Dull or worn blades
Scalping Incorrect cutting height or incorrect deck adjustment, or bent blades
Excessive vibration Clogged deck or damaged belt drive system 
Hydrostatic transmission problemAir in the system (cavitation)

Kubota Mower Problems And How To Fix Them

There aren’t many Kubota zero turn mower issues that you can’t prevent with proper maintenance. When problems do arise, they are generally easy to fix. Below is a rundown of the most common lawn mower problems and how to solve them.

1. Difficult to Start

A difficult-to-start vehicle is always a cause for concern, but the first thing to check is the fuel. A low fuel level or stale fuel could cause starting problems.

Next, check the parking brake and the seat safety switch. Disengage the parking brake if necessary or fix it if it’s stuck. If stuck, don’t fix the parking brake yourself. A faulty parking brake could fail to engage when you need it the most and is an accident hazard. Contact your service center to repair or replace the part.

Another potential cause could be the seat safety switch. The seat switch engages when you stand up from the seat, preventing you from operating the mower if you’re not actually seated. Sometimes, this switch could get stuck, or its wires might get loose. Inspect the switch and reconnect any loose wires. Alternatively, replace it with a new switch to solve the starting problem.

2. Not Enough Engine Power in Kubota Zero Turn

If your mower starts but loses power as you’re using it, you may deal with a defective spark plug, clogged filters, or fuel supply problems. 

Fuel supply problems can happen due to low fuel levels but also because of a defective or clogged carburetor. A defective carburetor needs to be replaced, but you can clean it if it’s clogged with a carburetor cleaner – simply spray the product until you get all the gunk out and fresh cleaner starts oozing out of the passages.

Dirty fuel could also cause a stalling problem, but all you have to do is to drain the old fuel and add fresh gasoline. If the fuel is dirty, the filters might be clogged too, and you’ll have to replace them.

How to maintain a Kubota zero-turn mower

3. Engine Running Roughly

In addition to reducing power, a defective spark plug, a defective carburetor, or a clogged carburetor could also cause the engine to run roughly. You can follow the steps above to solve the issue.

4. Engine Overheating

Kubota manufactures reliable engines that rarely overheat. When they do, the culprit is most likely an overload caused by grass clippings packing beneath the mower or mowing the grass when it is wet.

Another potential culprit is a cooling issue caused by insufficient cooling oil, a clogged oil filter, clogged air intake, or dirty cooling fins.

All these problems are very easy to fix by adding more oil, replacing the filters if they are dirty, and cleaning the fins.

5. Starter Not Functioning

Starting a zero turn mower is generally easy, thanks to the convenient starter button. But what to do if the button doesn’t work?

The most common culprit is the battery. You should check the terminal connections and tighten any loose wires. If the connections are corroded or rusted, you can clean them with a baking soda paste by scrubbing it on the terminals with a toothbrush. Clean the wire clamps in the same way, then wipe off excess paste. Let everything dry completely before connecting the battery again.

If the battery doesn’t charge or it oozes a liquid, you should replace it. If the problem persists, you should replace the starter button.

6. Starter Is Weak And Lights Become Dim

A weak starting, a mower losing power, or headlights that become dim as you’re mowing have one factor in common: a defective battery that isn’t charging sufficiently. There is only one thing to do. Replace the battery with a new one.

7. Battery Not Recharging

Vehicle batteries don’t go flat as long as you’re using the vehicle regularly, and zero turn mower batteries are no different. However, your Kubota’s battery could lose its charge during periods of inactivity

Leaving the battery discharged for too long could shorten its lifespan. For this reason, you should charge the battery periodically during the off-season. If the battery doesn’t charge, you should replace it with a new one.

8. Electrolyte Level Drops Rapidly

Like other riding mower brands, Kubota equips its zero-turn mowers and lawn tractors with lead acid batteries. These batteries contain electrolytes in the form of a liquid trapped inside the electrolytic cells. 

If the battery is defective, the cells could crack, and the liquid could start oozing out. A low electrolyte level in the battery can prevent the mower from starting, or it could cause it to lose power. Unfortunately, you can’t top up the electrolyte level, and the only thing to do is to replace the battery.

9. Operation Is Not Smooth in Zero Turn Mower

If your zero turn mower doesn’t have a power problem, but the operation seems rough, the most likely problem is a lack of hydrostatic fluid. Without getting into the nitty-gritty of how hydraulic systems work, you should know that hydrostatic oil is responsible for transmitting power within the machinery.

The hydrostatic fluid level could drop due to leaks. Adding more oil or replacing it with new fluid can solve the problem.

How to change hydrostatic oil on Kubota zero turn mower

10. Does Not Move While Engine Is Running

The mower starts but won’t move? There are a few potential culprits. One is the parking brake, which could be engaged. You should check it and disengage if needed.

A low level of hydrostatic fluid could also be a problem. The mower could also refuse to move due to a clogged carburetor or filters

Another thing to check is the bypass valve. This valve allows you to disconnect the wheels from the drive system, allowing you to push or pull the mower when it is in a neutral state. If you’ve engaged the valve recently for maintenance or repairs, you should check and make sure that you’ve disengaged it.

11. Blades Do Not Rotate

There is hardly anything more frustrating than getting ready to mow the lawn only to find out that the blades won’t spin. The main culprit is the PTO system, which is responsible for transmitting power from the engine to the blades.

A PTO system consists of a switch, clutch, pulley, and belt. Any of these components could be faulty or worn-out, so you should check them all and repair or replace them as needed.

12. Mower Belt Slipping

A worn belt is the most frequent reason why it slips over and over again, but not the only one. Debris stuck in the pulley, or a weak tension spring could also cause the belt to slip. Fixing the issue should start with identifying the problem.

Clean the debris and perform regular maintenance to keep the pulleys clean. You should also replace any worn-out or damaged parts.

13. Uneven Cut

Your mower leaving uncut grass can happen for a variety of reasons, including incorrect tire pressure, dull or damaged blades, or an unleveled mower deck.

Check the tire pressure first and adjust it to match the tire pressure recommended in your unit’s manual (do so on a hard, level surface for the best results). Proceed to check the deck level and adjust if necessary – the deck level could be the problem if you notice that the mower mostly cuts uneven when turning

If the tires have the right pressure and the deck is level, the problem is in the blades. Inspect them and replace them with new blades if they are damaged. If the blades are dull, take them off and sharpen them.

14. Streaking

If you notice strips of uncut grass but otherwise even grass cutting, you don’t have to worry about the tire pressure or the deck level. However, the blades could be a culprit. Another potential problem could be the way you’re driving the mower.

Zero-turn mowers aren’t that easy to figure out at first. Until you learn how to turn correctly, your patches might not overlap, and you’ll notice the lawn mower leaving streaks of grown grass behind. 

15. Blades Scalping

Lawn scalping is one of the most annoying things, usually caused by damaged or bent blades. Setting a too low cutting height could also lead to lawn scalping. Other potential culprits are the deck rollers. If these wheels are damaged, and you’re mowing on uneven ground, they might not adjust the deck’s level when riding over bumps, leading to scalping.

Depending on the cause, straighten the blades, adjust the cutting height, or replace the deck rollers.

16. Kubota Mower’s Excessive Vibration

One thing to know before delving into the matter is that all riding and zero turn mowers vibrate. However, if you notice an unusual level of vibrations, you may have to find the culprit and fix the problem. 

Likely causes include debris stuck under the deck, damaged pulleys or belts, and other mower deck problems

Fixing the issue is easy once you find the culprit. If it’s debris, clean it. Replace a damaged pulley or belt, fix the blades, or adjust the deck level.

17. Hydrostatic Transmission Problems

Aside from the low hydrostatic fuel levels we mentioned above, another common problem with hydrostatic systems is cavitation. This refers to air stuck inside the hydraulic system. When this happens, the power isn’t transmitted as it should, causing a drop in performance. Purging – or removing the air – could fix the problem. 

Summary

Fixing your Kubota mower issues isn’t difficult as long as you can find the culprit. We hope this guide can help you figure out what’s wrong so that you can solve the problem quickly and easily.