7 Common Kubota Z421 Problems & Solutions [Recall Info.]

The Kubota Z421 is an excellent mower for those who want quality performance without spending a fortune. However, like all machines, it can experience problems from time to time.

The most common Kubota Z421 problems are a weak fuel line needing replacing, tensioner springs breaking, which stops the mower from moving, and a rollover protective structure issue with a recall in place.

In this article, we will discuss some of the most common Kubota Z421 problems and how to fix them. This information will help you keep your mower running smoothly!

Kubota Z421 Won’t Move

One of the most common Kubota Z421 problems is that it won’t move. A number of things can cause this, but the most likely culprit is a problem with the drive belt.

If your mower’s drive belt is loose, damaged, or broken, it will prevent the wheels from turning. To fix this problem, you will need to replace the drive belt.

You could also be dealing with a problem with your hydro. Hydro issues can be complicated and expensive, but you’re specifically looking for tensioner springs. The tensioner spring can come loose, which will cause the mower not to move.

Here’s a video showing exactly how to change the spring:

Rollover Protective Structure Issue

Another common Kubota Z421 problem is the rollover protective structure or ROPS. The ROPS is a safety feature that is required by law on all ride-on lawnmowers.

This feature prevents the mower from flipping if you hit a large object or go over a bumpy piece of terrain. However, the ROPS can become damaged or even detached from the mower.

What’s important to know is there’s a recall in place for several Kubota mowers, including the Z421, because the rollover protective structure can loosen, which of course, poses a health risk.

The recall is for 2017-2018 models, in your case, the Z421KW-54 model; you can read more about the recall here.

Trouble Starting The Mower

If you need help starting your Kubota Z421, it could be due to several things. It could be something as simple as stale gas or a dirty air filter.

I’d always advise you to check the basics before moving on to more complicated issues.

Pull the blade engage switch up; if the blades don’t engage and there’s no sound, you may have a different issue. Firstly, check all the fuses, and make sure it’s not a simple fuse replacement.

The Z421 has an electric clutch that is attached under the crankshaft, are the wires connected? You’re looking for any loose or faulty wiring or any debris that may be impacting the engine.

Use your voltmeter to check the voltage you’re getting to the clutch harness. The clutch harness can be found under the engine, it should be reading 12 volts; anything less, and your mower is struggling for power.

If none of those solutions work, it’s time to get the machine to your local repair shop.

Belt Tension Spring Problems

It’s almost comical how common of an issue this is; the belt tension spring helps keep the belt tight, which is essential for two reasons.

The first reason is that it keeps the belt from slipping, which can cause many problems. The second reason is that it prevents the belt from breaking.

Unfortunately, the tension spring is known to break quite easily. It’s not uncommon to go through multiple belts every 50-100 hours of use.

Weak Fuel Pipe Line

Apart from replacing belt after belt, I’ve replaced my fair share of pipes in the fuel system. The fuel pipeline that comes standard with the Z421 is weak, it’s just one of those parts they cut costs on.

With all the debris that gets kicked up during use, cracks can appear in the fuel line, which then leads to leaks.

If you’re noticing sudden power loss, this is the likely reason why.

It’s a simple fix; you need to replace the pipe with a more sturdy, fit-for-purpose pipe that’ll last more than 100 hours of mowing!

Clogging Carburetor

An issue you’re likely to see with any small engine is a clogged carburetor. The carburetor is responsible for mixing the air and gas before it enters the engine.

If the carburetor is dirty or has debris in it, the engine will not run properly; the weak fuel line above doesn’t help this situation either. To clean the carburetor, you will need to:

  • Disconnect the spark plug wire.
  • Remove the air filter housing.
  • Remove the carburetor bowl nut.
  • Clean out the carb with a carb cleaner and a small brush.
  • Reassemble and try starting the engine.

Cleaning the carburetor should be as regular as changing spark plugs, fuel, and air filters.

Excessive Smoke From The Exhaust

Excessive smoke from the exhaust is never a good sign. It usually indicates that there’s too much oil in the engine, which can cause many problems.

If you’re noticing excessive smoke, check the oil level, and if it’s overfilled, drain some out. You should also check for any leaks, an easy way to do this is to put a piece of cardboard under the mower overnight, in the morning, and check for any oil stains.

If you can’t find any leaks and the oil level is correct, it’s time to take it to your local repair shop.

Frequently Asked Questions:

How much does a Kubota Z421 weigh?

Depending on the width of the mower deck, the Kubota Z421 weighs between 856lbs – 904lbs.

How do you start a Kubota Z421?

To start the Kubota Z421, you will need to turn the key switch to the “on” position, push down the brake pedal, and then push the starter button.

How much does a Kubota Z421 cost?

The Kubota Z421 typically retails for between $5,000 – $10,000, depending on condition.


Kubota has been in the business for over 100 years and is known for manufacturing durable, high-quality products. That being said, every machine has its issues, and the Kubota Z421 is no exception.

Having said that, overall, the Kubota Z421 is an excellent mower. Just be aware of the common problems, like the belt and weak fuel line going, have spare parts at the ready, and teach yourself how to swap them out.

Also, take note of the recall in place for the 2017-2018 models.