8 JD L120 Problems and relatively low $$$ fixes..

The John Deere L120 lawn tractor, produced from 2003 to 2005, belongs to the L100 Series and was manufactured in Greeneville, Tennessee, USA. It’s powered by either a 20HP or 22HP Briggs & Stratton gasoline engine and features a hydrostatic transmission, manual steering, disc brakes, a 48″ mid-mount mower deck, and the capability to attach a snowblower or blade. The original price was $2,299 in 2005, making it an affordable yet feature-rich option for many homeowners​.

The common challenges associated with the John Deere L120 range from smoke emission, loss of power during mowing, difficulty in starting, excessive vibration, and rough cutting to various engine problems. Some of these issues stem from mechanical failures, while others are related to maintenance oversights, such as using the wrong grade of gasoline, clogged fuel systems, or damaged spark plugs​​.

Addressing the problems with this lawn tractor is crucial whether you are considering purchasing one or already own it and are facing some challenges. By understanding the common problems and their solutions, you can make an informed decision or take the necessary steps to troubleshoot and fix the issues to ensure your mower operates effectively. Let’s delve into the most frequent John Deere L120 challenges, understand their causes, and learn how to troubleshoot them.

john deere l120 with problems tractor on green lawn

Igra-World has extensive experience in dealing with lawn tractors, with numerous mechanics boasting years of hands-on experience. Our customers frequently share their experiences and concerns regarding the truck, which mirrors the common issues discussed in various forums. One customer notably stated, “The rough cutting issue was a game-changer for me, but with a few adjustments, my L120 is back to its optimal performance!”

How To Troubleshoot The Most Common Issues:

Smoke Emission (severity: high) How to Fix: Turn off the switch immediately to prevent further overheating, clear the engine cover, and consult a professional mechanic if the issue persists.

Loss of Power During Mowing (severity: medium) How to Fix: Ensure you are not overloading the mower, check the grass type, and adjust your mowing strategy accordingly.

Difficulty in Starting (severity: medium) How to Fix: Change the old diesel, check the oil level, and ensure the brake pedal is depressed before starting.

Excessive Vibration (severity: medium) How to Fix: Inspect the engine, check for any attachments causing imbalance, and contact the seller if necessary.

Rough Cutting (severity: low) How to Fix: Ensure wheels and tires are balanced, check the blade sharpness, and consult a mechanic for a system checkup.

Various Engine Problems (severity: high) How to Fix: Regularly clean fuel lines, replace damaged spark plugs, and ensure you are using quality fuel.

Uneven Cut (severity: low) How to Fix: Adjust mower speed, check tire pressure, and ensure blades are sharp.

Electrical Issues (severity: medium): How to Fix: Ensure the battery is charged and cables are clean; replace the battery if necessary​​.

1. Smoke Emission

The most common issues causing smoke emission are a high ratio of oil to air in the system, clogged air filters, excess crankcase oil, insufficient engine oil, internal engine problems, or a malfunctioning carburetor​​.

The lawn tractor, equipped with a potent engine, can sometimes show signs of smoke emission, which is often due to a high ratio of oil to air within its system. Clogged air filters, a prevalent issue, result from debris and dirt build-up, hampering sufficient airflow in the tractor and leading to smoke emission. Excess crankcase oil or insufficient engine oil can also contribute to this problem, indicating an imbalance in the engine’s oil management.

In some instances, internal engine challenges or a malfunctioning carburetor might be the culprits behind smoke emission, signifying more serious mechanical issues that require immediate attention. Smoke emanating from beneath the mower, particularly around the mower deck area, often hints at blockages caused by debris accumulation, impacting the discharge mechanism​.

How to Fix Smoke Emission:

1. Identify the Source: Initially, pinpoint the source of the smoke—whether it’s coming from the engine or underneath the mower.

2. Check Air Filters: Inspect the air filters for clogs and clean or replace them as necessary to ensure proper airflow.

3. Inspect Oil Levels: Check the oil levels in the crankcase and ensure they are within the recommended range, topping up or reducing as necessary.

4. Clean Mower Deck: If smoke is emanating from beneath, clean the mower deck thoroughly to remove any debris blocking the discharge.

5. Inspect Carburetor: In case of persistent problems, inspect the carburetor for any malfunctions and seek professional help if necessary.

6. Regular Maintenance: Adhere to a regular maintenance schedule to prevent debris accumulation and ensure the engine is in good working condition.

7. Professional Inspection: If the problem persists, consult with a professional mechanic to diagnose and fix any internal engine issues.

2. Loss of Power During Mowing

The primary culprits behind the loss of power during mowing in the lawn tractor include a dirty mower deck, the height of the mower deck especially when dealing with taller or dense grass, and running the tractor on wet surfaces which can be taxing on the mower​.

The L120 is a remarkable lawn tractor designed to handle various mowing tasks efficiently. However, like any other mower, it can experience a loss of power during mowing, which may manifest as a reduction in speed and mowing power. One prominent cause of this problem is the height of the mower deck, which, if not adjusted properly, can struggle with taller, dense grass leading to power loss. Working on wet surfaces is another factor that can lead to this issue as it requires more power to cut through wet grass. Additionally, a dirty mower deck can hinder the mower’s performance.

Over time, the accumulation of grass clippings, dirt, and other debris on the mower deck can create a barrier that the blades have to work harder to cut through, thus leading to a loss of power. Ensuring that the mower deck is clean and free from debris, and adjusting the deck height to suit the type of grass being mowed, are practical steps towards alleviating this problem.

How to Fix Loss of Power During Mowing:

1. Adjust Mower Deck Height: Ensure the mower deck is at the correct height for the type of grass you are cutting. Lift the deck if dealing with taller or dense grass.

2. Clean the Mower Deck: Regularly clean the mower deck to remove any accumulated grass clippings, dirt, and other debris.

3. Avoid Wet Surfaces: Refrain from mowing on wet surfaces as it can strain the mower, leading to a loss of power.

4. Sharpen Blades: Keep the blades sharp to ensure they can cut through grass with minimal resistance, maintaining the mower’s power.

5. Regular Maintenance: Follow the manufacturer’s guidelines for regular maintenance to keep the mower in good working condition, preventing unforeseen loss of power during mowing.

3. Difficulty in Starting

The most common issues causing difficulty in starting the truck are stale or contaminated fuel, a clogged fuel filter, a dirty or faulty spark plug, and a discharged battery.

This model which is a part of the revered L100 series, came with a robust 20-HP engine, which, under the hood, harbors components that can be the culprits behind the starting difficulty. Stale or contaminated fuel can clog the fuel filter or hinder the proper ignition, a common issue especially after prolonged storage. A dirty or faulty spark plug can also prevent the engine from turning over.

Moreover, a discharged or weak battery may lack the necessary power to crank the engine. Ensuring these components are in good working order is essential not just for overcoming starting problems but for the smooth operation and longevity of your mower. The particular specifications of the L120, like its 20-HP engine and 42-inch mower deck, require a smooth starting mechanism to effectively harness the mower’s power and capabilities.

How to Fix Difficulty in Starting:

1. Replace old or contaminated fuel with fresh, high-quality fuel.

2. Clean or replace the fuel filter to ensure fuel flows smoothly.

3. Clean the spark plug with a wire brush, check the gap, and replace if necessary.

4. Charge the battery or replace it if it’s old or weak.

5. Check the oil level, replenish if low, and ensure the brake pedal is fully depressed before attempting to start again.

4. Excessive Vibration

The primary causes of excessive vibration are worn-out blades, loose bolts, uneven tires, a dirty air filter, or debris in the mower deck​​.

This model is a robust lawn tractor from the L100 Series, boasting a 20HP Briggs & Stratton engine and a 48″ mid-mount mower deck. The specifics of its construction can sometimes lead to excessive vibration if not maintained properly. For instance, worn-out or unbalanced blades can create an imbalance in the mower deck, leading to vibrations felt throughout the mower. Loose bolts, on the other hand, might allow unwanted movement, further contributing to the vibration. Uneven tires or a dirty air filter could affect the balance and operation, adding to the discomfort.

Lastly, debris caught in the mower deck might interfere with the blade movement, causing noticeable vibration. It’s vital to address these issues to prevent further damage and to ensure a smooth, comfortable mowing experience.

How to Fix Excessive Vibration:

1. Start by turning off the mower and disconnecting the spark plug for safety.

2. Inspect the blades for wear or damage and replace them if necessary.

3. Check for loose bolts and tighten them securely.

4. Ensure the tires have even pressure and clean or replace the air filter.

5. Clear any debris from the mower deck and surrounding areas.

6. If the vibration persists or is severe, consider contacting the seller or a professional mechanic for further assistance.

7. Regular maintenance—like blade sharpening, bolt tightening, and deck cleaning—can go a long way in preventing excessive vibration in the future!

5. Rough Cutting

The primary issues contributing to rough cutting are dull blades, improper deck height, unbalanced wheels and tires, and possibly a misaligned cutting system. These factors hinder the mower’s ability to deliver a clean, even cut, making your lawn appear untidy and poorly maintained.

The rough cutting problem stems from various mechanical components and operational settings of your truck. A predominant factor is the sharpness of the blades—dull blades can’t slice through grass cleanly, leading to uneven cuts and a ragged appearance. The deck height also plays a vital role; an improperly adjusted deck may either scalp the grass or barely cut it, depending on the setting. Besides, unbalanced wheels and tires can cause the mower to operate unevenly, aggravating the rough-cutting problem. The wheels need to be calibrated properly to ensure smooth operation.

An imbalanced mower can also result from unequal tire pressure, which affects the lawn tractor’s stability during mowing. Lastly, a misaligned cutting system could be at the root of the problem; if the cutting deck or other related components are out of alignment, it will significantly affect the cut quality.

How to Fix Rough Cutting:

1. Inspect Blade Sharpness: Check the sharpness of the blades. If they are dull, either sharpen them or replace them with new ones. Sharp blades are crucial for a clean cut!

2. Adjust Deck Height: Ensure that the deck height is set correctly according to the grass type and your lawn’s conditions. A proper deck height ensures that the grass is cut at the right level, promoting a healthier lawn.

3. Balance Wheels and Tires: Inspect the wheels and tires for balance. Make sure the tire pressure is equal, and the wheels are well calibrated. Balanced wheels and tires contribute to smoother mowing, reducing the chances of rough cutting.

4. Check System Alignment: If the above steps don’t resolve the issue, inspect the alignment of the cutting system. It may require professional adjustment to get it back on track, ensuring a smooth and even cut across your lawn.

6. Various Engine Issues

Various engine problems can plague the lawn tractor, affecting its performance and your lawn maintenance routine. A major culprit is dirty fuel lines—over time, impurities in fuel can clog the lines, causing a rough engine to idle and sometimes stall. Damaged or worn-out spark plugs also contribute to engine problems. They can cause misfires, reduced fuel efficiency, and even engine surges. Lastly, the quality of fuel used in your L120 is crucial. Low-quality fuel can cause the engine to work harder than necessary, potentially leading to overheating and other serious issues.

The lawn mower comes with a 22-horsepower engine that demands quality maintenance to function optimally. Furthermore, users have reported issues like engine popping at full throttle due to faulty spark plug wires, coils, and fuel cap vents. Ignition coils and spark plugs are essential for the engine’s ignition system, and any damage or wear can cause misfiring or lack of power. A clogged fuel cap vent, on the other hand, can create a vacuum in the fuel tank, affecting the engine’s fuel supply and subsequently its performance​.

How to Fix Various Engine Issues:

  1. Clean the Fuel Lines:
    • Locate the fuel lines connected to the fuel tank and carburetor.
    • Detach the lines and use a carburetor cleaner to flush them out.
    • Reattach the fuel lines securely.
  2. Replace Damaged Spark Plugs:
    • Locate and remove the old spark plugs.
    • Install new, quality spark plugs.
    • Ensure the spark plug gaps are set to the specifications in your user manual.
  3. Use Quality Fuel:
    • Empty the fuel tank of any old or low-quality fuel.
    • Refill with fresh, high-quality fuel recommended in your user manual.
  4. Check and Clean the Fuel Cap Vent:
    • Remove the fuel cap and clean the vent to ensure it’s free from dirt or debris.
  5. Inspect Ignition Coils and Wires:
    • Check for any visible damage or loose connections in the ignition coils and wires.
    • Replace if necessary.

7. Uneven Cut

Uneven cutting can be quite a nuisance as it not only compromises the aesthetics of your lawn but also can indicate underlying issues with your lawn tractor. Dull or damaged blades are often at the helm of uneven cuts. Over time, blades can become dull, which in turn makes them ineffective in cutting grass uniformly. Furthermore, a damaged blade might lead to a bent crankshaft, a grave issue that might require you to replace the lawn tractor entirely! Maintaining sharp blades is crucial to ensuring a precise cut each time.

Another common perpetrator of uneven cutting is imbalanced tires or incorrect tire pressure. When the tires are not balanced or inflated correctly, the mower deck’s level can be thrown off, resulting in an uneven cut. It’s imperative to maintain the correct tire pressure as specified in the manual to prevent such issues.

The level of the mower deck is a critical factor in achieving a uniform cut. An incorrectly leveled deck can cause one side to cut lower or higher than the other, leading to an uneven cut. Additionally, a clogged deck can hinder the blades’ movement, causing uneven cuts—regular cleaning to remove grass clippings and other debris from under the deck is essential.

How to Fix Uneven Cut:

  1. Check and Sharpen Blades:
    • Inspect the blades for dullness or damage.
    • Sharpen or replace the blades if necessary.
  2. Tire Pressure:
    • Check the tire pressure on all tires.
    • Inflate to the recommended pressure as per the manual.
  3. Level Mower Deck:
    • Ensure the mower deck is level from side to side and from front to back.
    • Adjust as necessary following the guidelines in the manual.
  4. Clean Mower Deck:
    • Remove any debris or grass clippings from under the mower deck.
  5. Inspect Crankshaft:
    • Check for a bent crankshaft especially if there was a recent blade impact.
    • Consider consulting a mechanic for a thorough inspection and replacement if necessary.
  6. Adjust Mower Speed:
    • Adjust the mower speed to ensure it’s suitable for the grass conditions.

8. Electrical Issues

Electrical issues on the lawn tractor are often due to a dead battery or faulty wiring—either of which can cripple the functionality of the mower. The L120 model is equipped with a robust electrical system designed to power its operations seamlessly, but like any electrical system, it’s susceptible to wear and tear. A dead battery prevents the tractor from starting, while faulty wiring can cause intermittent electrical connections leading to erratic operation. Starter solenoid failure is another snag; it halts the electrical current needed to start the engine, leaving you with a non-starting mower.

Malfunctioning safety switches—a mechanism designed to ensure the mower operates safely—can also lead to electrical problems. For instance, a faulty seat safety switch may prevent the engine from starting if it fails to detect the operator’s presence. Lastly, flickering dashboard lights are usually a sign of an unstable electrical system, often due to a failing alternator or battery. The specifications such as its 12-volt battery, emphasize the importance of a reliable electrical system in powering the various functionalities of the lawn tractor.

How to Fix Electrical Issues:

1. Battery Check: Ensure the battery is fully charged. If it’s old or weak, consider replacing it with a new one.

2. Cable Inspection: Inspect the cables for any signs of corrosion, wear, or loose connections. Clean the battery terminals and cable ends using a wire brush to ensure a good connection.

3. Starter Solenoid: If the starter solenoid is faulty, replace it to restore the flow of electrical current needed to start the engine.

4. Safety Switches: Inspect the safety switches for any malfunctions and replace them if necessary to ensure safe operation.

5. Wiring Inspection: Examine the wiring for any signs of damage, wear, or loose connections and repair or replace as necessary to restore the electrical integrity of the mower.

If You Don’t Already Own One, Should You Buy It?

The L120, with its potent engine, hydrostatic transmission, and attachment capabilities such as a snow blower or blade, does offer versatility for homeowners. However, there are notable concerns that might sway your decision. Common issues associated with this model include smoke emission, loss of power during mowing, difficulty in starting, excessive vibration, rough cutting, and various engine issues. These problems stem from both mechanical failures and maintenance oversights, necessitating a commitment to regular troubleshooting and repair.

User reviews suggest that while the model can perform well, addressing the frequent issues can be a hassle. One customer shared, “The rough cutting issue was a game-changer for me, but with a few adjustments, it is back to its optimal performance!” This suggests that with some effort in addressing its common issues, the truck can be a reliable machine, although the necessity for adjustments might deter some potential buyers​​.

In comparing this machine to a similar model from a competing brand, the Cub Cadet XT1 LT42, it’s found that the Cub Cadet model often comes at a lower price point while still offering comparable performance and easier maneuverability. The Cub Cadet XT1 LT42 is praised for its comfortable seat, tight turning radius, and easy-to-use hydrostatic transmission, making it a user-friendly option​​.

If you don’t mind dedicating time to maintenance and troubleshooting, this model could be a viable option, especially if you require the versatility it offers with additional attachments. On the other hand, if you’re looking for a more user-friendly and less maintenance-intensive option, you might want to consider the Cub Cadet XT1 LT42 as an alternative.

Why Trust Igra World?

At Igra World, we embarked on a meticulous journey—investigating and documenting common issues with this truck. They delved deep, analyzing and diagnosing prevalent issues such as smoke emission and loss of power during mowing. Consulting with industry peers, they fostered a collaborative environment where knowledge on resolving these issues flourished. Rigorous testing of proposed solutions followed, ensuring accuracy and efficacy.

The fruit of this diligent labor was a comprehensive troubleshooting guide, compiled with care and expertise. Recommend the L120, we admire its robustness—when maintained well, it’s a worthy companion for any lawn care aficionado.

About Jeff Henderson

Have a question regarding your lawn tractor? Igra World writer Jeff Henderson may have covered it already on this site, if not you can contact him at jeff.h@igra-world.com and (417) 414-5099 if you have an problem you can't find an answer to. Jeff is a part time tractor mechanic and landscaping company owner who lives in Springfield, Missouri. He has over 10 years of experience in tractor repair and small engine repair, and has worked with John Deere, Husqvarna, Toro, Troy Bilt, Cub Cadet and Kubota equipment.

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