7 Most Common Kubota z421 Problems & Troubleshooting

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By Marvin Tucker

Farming Equipment

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When you think about a mower that presents a compromise between residential and commercial mowers, the Kubota z421 will be a top candidate. It is an efficient mower with the ability to trim large yards. This mower belongs to a big family of Kubota zero-turn mowers, such as the Kubota GR2120.

Kubota z421 is fast and efficient, but so far, there is no mower without problems. There are always issues with mowers that do not entirely satisfy users. The vast majority of problems with the Kubota z421 mower are: starting difficulty, engine running rough, unusual exhaust, or the blades not spinning.

 If you want to understand more about these problems, keep reading, and we will provide you with details and solutions to each one.

The Most Common Problems with Kubota z421

Despite issues and complaints, Kubota z421 mowers are not the exception. These are a few exceptions that happen with unlucky users, either due to faulty parts or maintenance negligence. The good news is that these problems can be solved and even prevented with proper care and efficient use.

1. The Engine won’t start

This is one of the most repetitive Kubota z421 problems. Several causes can prevent the engine from starting. For instance, there could be switches that are not in their correct position.

So, make sure that the parking brake is applied correctly. Also, it is worth checking whether the PTO switch is turned off.

Sometimes, it results from a fuel problem, just like the ones in the Kubota MX5400. So checking out the fuel system is the right step. There could be no fuel, and you will need to refill the gas tank.

Also, the fuel filter could be clogged or worn out. So, it would help if you replaced it. Ensure the fuel is not expired due to improper storage, which could lead to poor performance and long-term engine damage.

2. The Engine is running rough

This is another one of the most common Kubota z421 problems. You can notice that the engine bogs down after starting. A spark plug that has been damaged may cause this problem.

A damaged plug can be recognized by its look. A thick coating of carbon deposits will be present. Also, it could look corroded or burned. Getting a new spark plug is a right action. It is easy to install a new plug.

The carburetor is another main suspect in a sluggish engine. The carburetor is responsible for keeping the proper air and fuel ratio. But just like any other part of the mower, it can get unclean with old gasoline buildup.

Such buildup can clog up the carburetor and make it unable to organize the correct blend of air and fuel. In this case, you will have to clean the carburetor to get its old performance back.

3. Strange Dark exhaust

You should not see excessive, colored exhaust from your Kubota z421. You must inspect the fuel quality if you notice dark or grayish exhaust. Also, checking the filters to unclog the plugged ones is the second step. Taking a look at the mower’s choke is another culprit.

The choke valve is supposed to help warm up the engine while starting during cold seasons. So, it opens up to let some air in, then automatically closes to allow a proper blend between air and gasoline.

If this valve gets faulty for any reason, it will become stuck and won’t open or close as it should. Then, you will need to correct its position. You might need to lubricate it with some oil.

Sometimes, the linkage cable might be too tight to let the valve open and close properly. You can loosen its bracket a bit to allow proper motion.

4. The Blades are not rotating

Blade problems are not just common in this Kubota model, but they are also happening in other zero-turn mowers, including the Ferris IS700z. The reason could be as simple as something obstructing the mower’s deck.

In this case, you will need to inspect the deck by lifting and searching for obstructions.

Then, you will have to remove it using a tool such as a concrete block. While inspecting the deck, checking out the blade for bending or corrosion is an intelligent step. Sharpening or changing the blades, in this case, is recommended.

5. Mower is not moving despite engine start

If your Kubota z421 is not moving or goes forward, you will need to check the brakes. Sometimes, you might want to check whether the parking brake is engaged.

This can easily prevent the machine from moving. You must release the brakes by pressing their pedal and increasing the drive speed simultaneously.

This can be an indication of a problem in transmission. For instance, the fluid can be insufficient. You will need to refill in this case, and checking the transmission filter is also required for proper transmission.

6. The Mower scalps the grass

Judging any mower is based on the efficiency of the cuts and not ruining the turf. You could gradually ruin your lawn when your Kubota z421 starts to scalp the grass.

You could be the one to blame for this problem. You could have determined a low height for the cutting. Also, this might be due to the nature of the lawn itself. It could be made of uneven and bumpy terrain.

Readjusting the height of cutting is the proper action in the first case. But if the lawn has bumps and uneven ground, you must change the anti-scalp rollers.

Adequate adjustment of these rollers will keep the mower deck from contacting the lawn. While you are at it, it won’t hurt to check the pressure of your tires. Correct pressure contributes to reducing the chances of close contact.

7. The lawnmower will not start 

The most specific cause for this problem is a faulty start switch. You will need to test the control using your ohmmeter to ensure the switch’s fault.

This test can show whether the power works smoothly or poorly. If you have difficulty turning the switch, you will have to get a new one.

Checking the battery is also recommended whenever there is a problem turning on or starting this mower. The battery life could have expired, and there will be a need to replace it.

Sometimes, the battery could be unresponsive due to corroded parts, such as the terminals. In this case, you will need to thoroughly and carefully clean the terminals. After cleaning them, you will need to apply some lubricating grease to them.

Kubota z421 Problems: are they a deal breaker?

Despite these common Kubota z421 problems, most users are entirely content with their mowers. This mower is backed with great features such as fast performance, covering big yards, and a superior Kawasaki engine.

Yet, some users experience various issues while using this mower. Generally, these problems can be handled when you keep maintenance routines on schedule.

It does not matter if you are not a DIY fan; you can always seek professional help to address technical issues or turn to your dealer.

However, one of the most significant advantages of using this mower is its low cost compared to other machines with comparable features. The Kubota Z421 offers you versatility without exceeding your budget.

As for repair costs, you will not be forced to drag this mower to a repair shop every couple of months. It can give you longevity, provided you take good care of it.

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