Mountfield lawnmowers are known to be compact, lightweight, and easy to maneuver. The ride-on models feature a Stiga engine providing ample power, while the seating position allows for improved visibility when operating the machine over extended periods.

When using a Mountfield lawnmower, there are a few potential issues to be aware of. These common problems, such as blade bosses shearing off, broken shear keys, and gas tank or gas line blockage, can be difficult to identify but are quickly solved if detected. Read on to discover the best methods to solve your problem.

Here are some of the most common Mountfield mower problems:

1. Blade bosses sheared off

Many Mountfield lawnmowers have blade bosses that shear off, which can be costly. Fortunately, there is an affordable and easy solution – installing a new blade boss.

These are widely available from most dealers online and the installation process is straightforward – tighten the blade bolt to the correct torque setting.

If you are unsure of how to replace the blades on your push mower, a blade replacement kit is advisable.

Home improvement stores often carry kits that include replacement nuts and blades, providing an accessible and straightforward method of replacing them at an affordable cost.

If your blades are damaged, you may have to get a new set. This usually costs just a few dollars, and they can be reinstalled in approximately ten minutes. Contact your local dealer for assistance with installation if needed.

2. Obstructions in the fuel tank or fuel line may be present

If your Mountfield mower is not functioning correctly, you should investigate the cause. Possible issues may include a blocked gas tank or line.

When carrying out this task, safety guidelines should be followed. In addition, a faulty carburetor can lead to hydro-locking, meaning gas in the cylinder blocks movements.

It is important to use a fuel stabilizer when traveling by trailer with the mower since without it a no-start condition could occur. A fuel stabilizer can be used to both protect the Mountfield mower when not in use and help start it again in spring.

If the fuel tank appears cracked, this may have been caused by an object hitting the lawnmower. In some cases, the fuel line might even become snagged on a shrub and snap off.

Fortunately, replacing the fuel tank can be simple if done correctly – usually held in place with spring clamps, the fuel line needs to be detached before doing so.

3. A clogged carburetor

To troubleshoot a clogged carburetor on a Mountfield lawn loader, adequate familiarization with carburetor inspection is essential. Oil level should always be checked before each use and at least once monthly if the machine is used more frequently.

Also, watch for increased oil consumption when working on inclines or whenever the oil is leaking through the crankcase breather. A clogged carburetor might be the cause of difficulty starting the Mountfield machine. The Mountfield mower’s carburetor can be clogged by the choke, which is responsible for mixing the air and fuel before drawing it into the engine.

The carburetor has different passages that open at various throttle positions. At idle, fuel passes through the idle circuit to join with the air stream. The choke can control fuel flow during start-up and cold weather. If the problem continues, it may be necessary to replace it.

Applying voltage to the coil triggers the solenoid to open, allowing fuel to enter. Applying voltage to the coil will cause the solenoid to unlock and grant fuel entry. However, they could potentially become jammed or clogged. Therefore, checking your carburetor before using your mower is essential.

4. Broken shear key

The blade of a Mountfield mower may not release if the shear key is broken, which can be caused by storage. If you experience any failure, it is important to have broken shear keys on Mountfield mowers repaired at a local dealer, as this is a common issue.

The flywheel key in a lawn mower can become damaged, resulting in poor engine performance or difficulty starting the engine. This fault can occur if the mower strikes a non-mowable object and the crankshaft becomes damaged. A malfunction in the ignition module or safety interlock system could lead to flywheel key breakage.

5. Oil level

If the mower doesn’t run, the first step is to inspect the oil level. Look for a small screw cap that can be wiped off with a cloth and compare it to the high and low marks on the dipstick. It should be in between those marks.

To ensure an exact reading, move the mower to a level surface and locate the labeled dipstick – typically colored differently and labeled “oil” or “oil can”. Checking the oil level is a quick task that can be done while the engine is off.

The oil cap also serves as the oil filler. The dipstick can be checked to view the oil level. The upper mark indicates that it is full, while the lower mark signals that it is low.

There may be hatched markings on the dipstick suggesting extra oil can be added if necessary. Ensure the level is above “additional oil is required” if that mark appears on the dipstick.

If gas is identified from the exhaust valve, applying WD40 to the stem of the valve may be beneficial. Additionally, pressure should be maintained on the intake valve and it should either be closed or left partially open.

The carburetor forces the mixture out of the chamber during compression. If the mixture is excessive, it may be necessary to clean the carburetor and rebuild the engine.

6. No spark

To begin the Mountfield mower, ensure that the control wire is connected securely to both the flywheel brake assembly and engine coil; if it is not, this can be a cause of why the mower does not produce a spark.

The flywheel brake assembly and engine coil must be connected to the control wire securely to ensure that the mower successfully starts; a loose connection can result in a lack of spark. It may be necessary to dismantle the cowl and detach the flywheel (if applicable) from above the engine to determine the status of the control wire.

If the issue is fuel-based, check the carburetor for dirt or water in the float bowl as this can prevent a spark. Likewise, a faulty ignition coil will result in a no-spark condition and must be replaced. After removing the old spark plug, mount a new one – however, it may not improve performance significantly. To check the ignition coil, connect an in-line spark tester to the spark plug boot and observe for spark.

If no spark is detected, the ignition coil should be checked. Other potential causes should also be considered if this does not solve the issue. A faulty ignition coil can make starting a mower hard, so it may be best to begin in a garage. Portable spark testers may also assist.

7. Clogged needle valve

The needle valve near the carburetor should be inspected if the Mountfield mower is sluggish when idling. The carburetor bowl needs to be removed to check for any blockages in the needle. Verify that a spring connecting the float hinge to the needle valve is present. If it is not, determine if it has been obstructed.

If the jet is loose, turn it clockwise a quarter turn. Take care not to over-tighten it since this could harm the soft tip. Additionally, check the float – on some engines, a blocked float could allow fuel to seep out.

The engine may be upside-down, leading to fuel leakage and preventing proper float operation. This could cause a fire. If there is a broken cable between the float and the engine, it needs to be located and repaired promptly.


To repair a sluggish or stuck needle, the linkage between the throttle body and air injector must be disconnected and adjustments need to be made to the idle speed. After that, apply a lubricant solution to the needle valve.

After cleaning the valve, run the mower several times. If the issue continues, obtain a repair from a store or reach out to Mountfield mower manufacturers for assistance.

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