John Deere 425 Problems (All Reasons + Solutions)

The John Deere 425 is a popular lawn and garden tractor that is known for its reliability and durability. However, like any machine, it can experience problems from time to time. 

There are a number of John Deere problems, among which the engine not starting or taking a long time to start is very common. Other than those two, the user could be facing other engine problems like overheating, misfiring, etc. Also, there could be electrical issues with the lights, starter, or battery.

Throughout this article, we will provide tips on how to troubleshoot and fix some common John Deere 425 issues.

John Deere 425 Starting Problems

Problems Reasons Solutions
Engine will not start Clogged fuel system Clean the fuel pump, fix the fuel line, replace fuel filter
Spark plug failure Spark plug needs cleaning or a replacement
Safety switch failure Replace the faulty switch
Incorrect carburetor adjustment Readjust the carburetor
Engine takes a long time to start Damaged throttle cable Replace the throttle cable
Problematic starter  Replace the starter

Problem 1: The Engine Will Not Start

In addition to serious issues, there are some simple mistakes at the root of this. Incorrect fuel grade, stale fuel, or no fuel in the tank are examples.

In case of a fuel shortage, just refill the tank. Also, be sure you use gasoline that has an 87-octane rating.

John Deere 425 Engine Will Not Start
Source: Tractordata

Your engine may also not start if the fuel is stale. Fuel should have a bright color and a pleasant smell. If it doesn’t smell like regular gasoline and looks kind of dark, then refill.

Reason 1: The Fuel System Clogged

If the fuel tank is full and the fuel is okay, then it could be that the fuel is not reaching the engine. That could be because of a clogged fuel system. 

The fuel system of the John Deere 425 consists of fuel lines, a fuel pump, and a fuel filter. Ensure that none of these components are blocked.

  • Check the fuel lines for any bends or kinks that may be restricting the flow of fuel.
  • Check the fuel pump for any debris or foreign objects that may be preventing it from working properly.
  • Locate the fuel filter. It is typically located in the fuel line between the fuel tank and the carburetor or fuel injectors.
  • The fuel filter should be removed from the fuel line of the vehicle.
  • Inspect the fuel filter for any dirt or debris that may be clogging it.

If the fuel pump is clogged, clean the debris out of it. Fix the bends if the fuel line is restricted. You can also simply replace a clogged fuel filter instead of cleaning it. 

Reason 2: A Defect in the Spark Plug

A spark plug is a small device that ignites the air-fuel mixture that starts the engine. A possible defect in the spark plug may cause the engine to fail to start.  

  • First, you need to pop up the hood and remove the side panel.
  • Then you should notice the spark plug wire on the bottom.
  • Remove the spark plug wire to expose the spark plug. After that, you will need to remove it with the help of a socket wrench.
  • Check the spark plug for damage or corrosion.

A corroded spark plug must be cleaned using a corrosion cleaner. A damaged one must be replaced. The process is quite simple, here is a video of the complete process,

Reason 3: Safety Switch Failure

There are three safety switches in a John Deere 425: the seat safety switch, the brake safety switch, and the PTO safety switch.   

The first two switches are designed to prevent the tractor from starting if no one is sitting and if the brake pedal is not pressed, respectively. If they fail to function properly, the engine won’t start.

  • Locate the seat safety switch which should be under the seat.
  • You need to perform a continuity test with a multimeter to see if it’s good.
  • Set the multimeter to the resistance setting.
  • Touch the leads of the multimeter to both terminals of the seat safety switch. 
  • If the seat safety switch is functioning properly, the multimeter should show a low resistance value, typically less than 50 ohms. 
  • If the multimeter shows a high resistance value or no reading at all, the seat safety switch may be damaged.
  • Perform the continuity test similarly on the brake safety switch.
  • The brake safety switch can be found under the hood to the left of the brake pedal.

You will need to replace any switches that do not work.

  • Disconnect the spark plug wires to prevent the engine from starting accidentally.
  • Locate the electrical connector for the brake safety switch. The connector will typically be a small, rectangular plug with wires coming out of it.
  • Squeeze the tabs on the sides of the electrical connector and pull it apart to disconnect it from the brake safety switch.
  • Locate the mounting screws or bolts that hold the brake safety switch in place. There may be one or two screws or bolts, depending on the design of the switch.
  • Use a screwdriver or socket wrench to remove the mounting screws or bolts and take out the brake safety switch.
  • Once the brake safety switch is removed, you can install a new one in its place by reversing these steps. 
  • Be sure to use the correct size and type of mounting screws or bolts to secure the new brake safety switch in place.
  • Follow the same procedure for removing the seat safety switch which is located under the seat.

Reason 4: Incorrect Carburetor Adjustment

The carburetor on a John Deere 425 lawn tractor is responsible for mixing the right amount of fuel and air and delivering it to the engine.

In the event that the carburetor is not adjusted properly, the engine may run poorly or fail to start.


If all the other components are fine, then you can conclude that the issue is in the carburetor adjustment. So, you will need to readjust the carburetor. Here is a video describing the whole process-

Problem 2: Engine Takes a Long Time to Start

If your John Deere 425 engine is taking a long time to start, then it could be an issue with the spark plug, stale fuel, or restricted fuel lines. There was already a discussion of these topics in the last section.

Except for these, there are a couple more problems that can contribute to this.

Reason 1: Damaged Throttle Cable

The throttle cable transmits throttle lever movement to the carburetor, which controls fuel and air delivery to the engine. A worn or damaged throttle cable will not perform its job properly.

Diagnosis and Solution:

Checking the throttle cable is a complex and lengthy process. So, it would be better to consult an expert. However, if you insist on doing it yourself, here is a video showing the complete procedure-

Reason 2: Problem with the Starter

A problem with the starter motor or the solenoid will cause your lawn tractor to not start or take a long time to do so. In this situation, a diagnosis of the starter motor is mandatory.

Before moving on to the starter motor, you should check if your battery is charged. You can check that by connecting the two probes to the battery terminals. The battery voltage should be 12.6 volts.

  • First, turn off the engine and remove the key from the ignition to ensure that the electrical system is safe to work on.
  • Remove the hood and then the engine cover.
  • On the side of the engine near the fuel tank, the starter is located.
  • Examine the cables that go from the battery to the starter. Look for any damage or corrosion on the cables, such as frayed wires, cracks in the insulation, or greenish-blue corrosion on the metal connectors. 
  • There should be no loose connections between the battery and the starter. Make sure the cables are securely attached to both the battery and the starter. 
  • Now, you will need to check the starter solenoid. It should be near the starter motor.
  • Make sure the multimeter is set to “continuity” and place the probes on the solenoid terminals. If the solenoid is functioning properly, the multimeter should beep or display a reading indicating continuity.
  • Before removing the starter, disconnect the connection from the battery to the starter.
  • The starter is screwed onto the engine. You will specifically need a T40 screwdriver to unscrew them. Once you do that, the starter should come right off.

Once you follow these steps, you will need to test the functionality of the starter motor. Here is a video on how to test a starter motor.


If the connections are loose, you will need to connect them properly. Corroded connectors should be replaced. In the event of a non-functional starter motor, you’ll have to get a new one.

John Deere 425 Engine Problems

Problem  Reason  Solution
Engine running rough Clogging cooling fans Clean the cooling fins
Ignition system malfunction Replace spark plug or ignition switch or coil 
Dirty air filter Replace air filter
Choke cable stuck Reconnect or replace choke cable
Engine Misfires Faulty spark plug Replace spark plug
Carburetor misadjustment Readjust carburetor
Ignition coil defect Replace ignition coil
Engine overheating Clogged cooling fins Clean the cooling fins
Overloaded engine Maintain the engine
Engine knocking Clogged cooling fins Clean the cooling fins
Misadjusted carburetor Readjust carburetor
Overstressed engine Maintain the engine

Problem 1: Engine Running Rough

A number of problems can cause your John Deere 425 engine to stall or lose power. Among them, clogged cooling fins or air filters, ignition issues, and choke cable sticking are common.

Also, a loose starter connection may also cause this issue, which we have already covered in the previous section.

Reason 1: Clogged Cooling Fins

The cooling fins on a John Deere 425 engine are responsible for dissipating heat and keeping the engine cool. If the cooling fins become clogged, it can cause the engine to stall and potentially cause damage.

Kawasaki Engines
Source: Kawasaki Engines
  • First, turn off the engine and allow it to cool down. The cooling fins will be hot, and it is important to allow them to cool down before attempting to clean them.
  • Locate the cooling fins on the engine. They are typically located on the cylinder head and the engine block.
  • Check for clogging or dirt in the cooling fins.

Clogged cooling fins must be cleaned. The best way to clean it is to use a brush or a dry cloth. But do it gently so that they don’t get bent or damaged.

Reason 2: Ignition System Malfunctioning

The ignition system consists of an ignition coil, switch, and spark plug. We have already described how to diagnose a faulty spark plug. It is now time to take a closer look at the other two.

  • First, turn off the engine and remove the key from the ignition to ensure that the electrical system is safe to work on.
  • Locate the ignition coil. It is typically located near the spark plugs or the engine block.
  • Test the ignition coil using a multimeter. Place the probes on the ignition coil terminals and set the multimeter to the “resistance” setting. The multimeter should display a resistance reading.
  • Compare the resistance reading to the manufacturer’s specifications for your engine.
  • Locate the ignition switch. It is typically located on the dashboard or control panel of the lawn tractor.
  • Test the ignition switch using a multimeter. Set the multimeter to the “continuity” setting and touch the probes to the terminals on the ignition switch. If the switch is functioning properly, the multimeter should beep or display a reading indicating continuity.

A faulty ignition switch will have to be replaced. 

  • Disconnect the battery to ensure that there is no electrical power to the ignition switch.
  • Remove any bolts or screws that are holding the ignition switch in place.
  • Disconnect the wires from the ignition switch. Make a note of which wires are connected to which terminals, as you will need to reconnect them to the new ignition switch.
  • Install the new ignition switch. Connect the wires to the appropriate terminals on the new switch, and secure the switch in place using bolts or screws.
  • Reconnect the battery.
  • Test the ignition switch to make sure it is functioning properly.

Similarly, a faulty ignition coil needs to be replaced too. 

  • Remove any bolts or screws that are holding the ignition coil in place.
  • Disconnect the wires from the ignition coil. Make a note of which wires are connected to which terminals, as you will need to reconnect them to the new ignition coil.
  • Install the new ignition coil. Connect the wires to the appropriate terminals on the new coil, and secure the coil in place using bolts or screws.
  • Reconnect the battery.

Reason 3: Dirty Air Filter

The air filter is responsible for removing dust, debris, and other contaminants from the air before it enters the engine. If the air filter becomes dirty or clogged, it can restrict the airflow to the engine and cause rough running.

  • First, turn off the engine and remove the key from the ignition to ensure that the electrical system is safe to work on.
  • Locate the air filter housing. It is typically located near the carburetor, at the base of the engine, or near the air intake. The housing is typically a plastic or metal box with a removable lid or cover.
  • Open the housing by removing any clips, latches, or bolts that are holding the lid or cover in place.
  • Once you have opened the housing, you should be able to see the air filter. It will typically be a rectangular or cylindrical element made of foam or paper.
  • Check for dirt or debris stuck in it. 

Replace the air filter with a new one if it’s dirty.

Reason 4: Choke Cable Stuck

If the choke cable on your lawn tractor or other small engine is sticking, it can cause issues with the engine’s performance

  • The first thing you want to do is remove the hood from the tractor.
  • Disconnect the connector to the lights 
  • With the hood off you can easily see the cables 
  • Loosen each screw that holds the cables.
  • Check for damage or wear and tear.

If the choke cable is damaged, you will have to get a new one. You will probably have to replace the whole set, along with the throttle lever and cable.

If the cable seems fine, you can lubricate it using penetrating oil or a silicone-based lubricant.

Problem 2: Engine Misfires

Your John Deere 425 may misfire because of a faulty spark plug, carburetor misadjustment, or ignition coil defect.

Problem 3: Engine Overheating

A clogged cooling fin, too little or too much oil in the fuel tank, or stale or low-quality fuel may cause the John Deere 425 engine to overheat.

Other than these, an overloaded engine can also cause the engine to overheat. Here are some tips you can follow to reduce the stress on your engine.

  • Maintaining proper tire pressure: Make sure that the tires on your lawn tractor are properly inflated. A low tire pressure can cause the engine to work harder, increasing the load on the vehicle.
  • Mowing at the correct height: Keep the mower deck at the correct height, this will reduce the load on the engine and improve the overall performance of the lawn tractor
  • Avoiding Overloading: Avoid overloading the lawn tractor by not carrying or pulling more weight than the tractor can handle.
  • Using the correct oil grade: Make sure to use the correct oil grade for your engine, using the wrong oil can cause increased engine wear and add unnecessary load on the engine
  • Keeping a good maintenance schedule: Regularly maintain the lawn tractor according to the manufacturer’s recommended schedule. This will ensure that the engine is running at optimal performance and reduces unnecessary load on the engine.
  • Clearing heavy grass before mowing: Avoid using the lawn tractor on heavy loads like thick or high grass, if the grass is high or thick, consider using a machete first to reduce the load on the engine.

Problem 4: Engine Knocking

In some cases, engine overheating can cause a knocking sound in your John Deere 425 engine. So, check for clogged cooling fins, a low engine oil level, a misadjusted carburetor, and an overstressed engine. 

John Deere 425 Electrical Problems

Problem Reason  Solution
Lights don’t work Light switch, connection or the light malfunctioned Replace or repair faulty component
Battery doesn’t charge Corroded terminal or dead battery cell Clean corrosion or replace battery

Except for engine issues, a John Deere 425 user can experience electrical issues with the light, the battery, or the starter.

Problem 1: Lights Don’t Work

If the lights on your John Deere 425 do not work, it could be the switch, the connection, or the light itself.

Here in this video, you can find out about the whole diagnosis process.

Problem 2: Battery Doesn’t Charge

There are possibly two reasons why your John Deere 425 battery is not charging. The first is that the connection between the battery cables and the connectors is loose or corroded somehow. 

In this case, disconnect the battery cables and reconnect them properly. Look for corrosion in the terminal. If the terminals are corroded, you can clean them using a corrosion cleaner. (our pick: NOCO E404 Battery Terminal Cleaner Spray and Corrosion Cleaner with Acid Detector)

The second reason would be damaged battery cells. In such a case, it would be advisable to replace the battery immediately. This video of the whole process should help you.

John Deere 425 Maintenance Tips

Here are some maintenance tips that will help you extend the life of your John Deere 425 lawn tractor. 

  • Regularly check and change the oil and oil filter. Use the recommended oil grade for your tractor and change it according to the manufacturer’s recommended schedule.
  • Check the air filter and replace it if it is dirty or clogged. A dirty air filter can restrict airflow to the engine and cause poor performance.
  • Check and maintain the proper tire pressure. Under-inflated tires can cause the engine to work harder, resulting in increased load.
  • Keep the mower deck and blades in good condition. Make sure the mower deck is adjusted correctly, and the blades are sharp, to ensure a clean cut and good performance.
  • Make sure belts and pulleys are in good condition and replaced when necessary. A damaged belt can cause vibration and affect performance.
  • Maintain a good charge and good condition of the battery at all times. Cold weather can cause the battery to lose charge faster, so make sure it is properly charged before use.
  • Keep the tractor clean. Regularly clean the tractor and remove any debris or grass clippings that may have accumulated on the machine.
  • Keep the fuel tank clean, you can add a fuel stabilizer and drain the tank before storing the tractor for a long time.


What engine is on the John Deere 425 tractor?

The John Deere 425 lawn tractor uses a 20 HP Kawasaki FD620D 2-cylinder, liquid-cooled V-twin engine. 

What is the life expectancy of a John Deere lawn tractor?

In general, John Deere riding mowers have a lifespan of about 8 to 10 years on average. This is approximately 4500-5000 hours of mowing over the lifespan of your machine.

Does the John Deere 425 have power steering?

The John Deere 425 tractor is one of the first tractors to offer power steering with an all-wheel steer (AWS) as an optional feature. Compared to the 2-wheel steer tractor, the AWS tractor had a wheelbase of 49.4″, as opposed to 50.4″ on two-wheel steer tractors.


The John Deere 425 is a powerful and reliable lawn tractor, but like any other equipment, it may have problems that need to be addressed. 

Some John Deere 425 problems include a clogged fuel system, a dirty air filter, and a malfunctioning ignition system. It’s important to regularly maintain and inspect the tractor to prevent and resolve problems.

However, if you are facing a specific problem and are unsure of how to address it, it’s always recommended that you consult a mechanic for specific guidance.

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