Riding Lawn Mower Sputtering? Fixes that Work

A faulty lawn mower can change a busy day set aside to mow your lawn into a garage session of fixing the problem. A sputtering sound indicates a mechanical problem with your lawn mower. So, why is your riding lawn mower sputtering?

A riding lawnmower may sputter due to old or contaminated fuel in gas tank, clogged fuel filter, blocked gas cap, faulty spark plug, carburetor issues and dirty air filters. Proper diagnosis can help to identify and fix the exact problem.

Why is my Riding Lawn Mower Sputtering?

Riding lawnmowers from longer storage come with many problems. If you haven’t tuned it up, your riding lawn mower won’t start at all or will sputter. Here are reasons why your lawn mower is sputtering and how to fix them.

1. Old Fuel in the Gas Tank

Allowing fuel to stay in the gas tank for more than a month can cause problems. It evaporates leaving behind sticky substances that clog the fuel filters, fuel lines, and carburetor components. The clogs prevent the free flow of fuel to cause the sputter.

This is why lawn mower sputtering is common in the spring after a long winter season break. Using cheap fuels that contain a high amount of ethanol can also cause your lawn mower to sputter.

How to Fix

If fuel has stayed in the tank for more than 30 days, discard it and refill the tank with fresh gasoline. When intending to store your lawn mower for a long period of time, be sure to add a fuel stabilizer to the fuel tank. Additionally, use the right type of gas for your lawn mower.

2. Presence of Moisture in Gas Tank

The presence of water in the gas lawn mower tank, fuel lines, and carburetor will cause problems in the engine. Moisture prevents proper ignition of fuel in the piston chambers and hence causes your lawn mower to sputter.

Water can enter the fuel tank through condensation or after leaving the gas cap loosely secured.

How to Fix

Check if there is water in the lawnmower gas tank. Drain off the contaminated fuel and let the tank dry completely before refilling it with fresh gas. Be sure to clean fuel lines, carburetors, and other components that might be contaminated with water.

3. Clogged Fuel Filter and Lines

Allowing fuel to stay in the tank for a long period of time will cause fuel filters and lines to clog. Using the same fuel filter for a while can also degrade its performance. The clogs can prevent fuel from reaching the carburetor and piston chambers for combustion.

Clogged fuel filters and lines are characterized by lawn mower sputtering, hard star, and an engine that runs and stops abruptly.

How to Fix

Use carburetor cleaner to unclog the fuel filters and lines. You might need to replace the filters and fuel lines in case they are damaged. Ensure the fuel is fresh and clean before refilling the gas tank.

4. Clogged Gas Cap Vent

The gas cap contains a tiny valve that allows air into the tank to facilitate the flow of fuel to the carburetor. If this valve is clogged, it will create a vacuum that prevents the free flow of fuels to the carburetor. This problem will cause your lawn mower to sputter.

How to Fix

Inspect the gas cap thoroughly to ensure it’s not clogged. Replace it if leaking or has cracks. Ensure the gas cap is tightly secured on the tank to prevent it from sucking in moisture to the fuel tank.

5. Faulty Spark Plug

A faulty spark plug can also cause poor engine performance. If a lawn mower is surging, the engine won’t start, or stops abruptly then you need to inspect the spark plug and its components.

The first part is the firing tip where a small metal bend to create a gap between the metal and the electrode. If the metal bend touching the electrode is broken, it will cause the mower to sputter. The second part is the housing which may be cracked.

How to Fix

The spark plug plays a key role in starting the engine. A damaged or loose spark plug can degrade engine performance. Replace the bad spark plug, if damaged or when exhibiting signs of wear and tear.

6. Clogged or Faulty Carburetor

Using the same lawn mower for a while without cleaning carburetor components can cause it to become filthy. Dust particles from the air and dirty fuel will cause the carburetor to clog over time. Such clogs with cause your lawn mower to sputter or experience a hard start.

Dirty or clogged carburetor components are simple issues you can fix on your own. However, there are other complex carburetor issues that can also cause your lawn mower to sputter. Such issues require professional help.

There are several jets on the carburetor that balances the amount of air that combines with fuel. If the jets are not set properly, they may cause the engine power to degrade.

How to Fix

Dismantle the carburetor carefully to clean and unclog its components. Use a carburetor cleaner to wash the carburetor bowl and other components that may be clogged. If you are not sure how to dismantle a carburetor, you can seek help from a professional.

7. Dirty Mower Deck

The buildup of dirt and grass in the mower deck may be the reason why your lawn mower is sputtering. It usually happens after cutting grass severally without cleaning the deck or after cutting wet grass in your lawn.

If you are using a side discharge mower, clogged grass in the deck disturbs the exit chambers causing the grass to clump instead of spreading evenly. The unnecessary pressure exerted on the blade will cause the engine to perform poorly.

How to Fix

Tilt your riding lawn mower on one side to expose the deck. Use a wood chisel to get rid of grass and other debris that may be clogging the deck. To prevent the deck from clogging, avoid cutting tall grass when it’s wet. It’s also important to clean your mower thoroughly after cutting grass.

8. Dirty Air Filter

Staying long without cleaning the air filter will cause the lawn mower to sputter. Dust and other debris from the air can accumulate and clog the air filters. Lawn mower takes in air through air filters which mix with fuel in the carburetor to cause ignition in the combustion chambers.

So, if the air filter is dirty, it will affect the free flow of air to the carburetor. Dirt can also accumulate in the part that leads into the carburetor to cause air obstruction.

How to Fix

A quick solution to this problem is simply to clean the lawn mower air filter with clean soapy water. Air it in the sun to dry completely before returning it to your mower. Replace it if damaged, be sure to choose one that is compatible with your unit.

Final Thoughts

It can be tricky to find out why your riding lawn mower is sputtering. However, some of the insights we have highlighted can help to identify and fix the problem. If the problem persists, it’s advisable to seek help from an expert.

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