Riding Lawn Mower Sputtering: Causes + Fixes

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It’s a familiar and frustrating scenario: you’re mowing your lawn on your trusty riding mower, and suddenly the engine starts sputtering and loses power. That lawn mower can be a real headache and leave your lawn care projects unfinished.

Your mower needs to run smoothly once more, and this can only be done by figuring out what’s causing the sputtering and fixing it. In this article, we’ll look at some of the most frequent causes of sputtering lawnmowers as well as practical solutions to fix the problem and get you back in action.

This guide will go over the main causes and fixes, regardless of whether the issue is due to poor fuel, filthy air filters, defective spark plugs, or another underlying issue. You can stop your riding mower from sputtering and improve its performance for flawless lawn care with a few focused inspections and maintenance procedures.

Riding Lawn Mower Sputtering (The Short Guide)

When a lawn mower sputters, start troubleshooting with the air filter; replace it if it is clogged. Also inspect the fuel line and carburetor, clearing any debris blocking proper fuel flow. Check the spark plug as well, swapping it out if it is fouled or faulty. Use fresh gas and fuel additives to prevent issues from stale gasoline. Spraying carburetor cleaner removes built-up dirt, causing sputtering. Regular maintenance, like oil changes and replacing filters, helps avoid many causes.

Why Riding Lawn Mower Sputters: 8 Causes and Fixes

Dirty Air Filter


A dirty air filter can be a cause of sputtering lawn mowers, as debris and dirt clog the filter over time, which restricts airflow to the carburetor. This reduced airflow leads to an improper air-fuel mixture in the carburetor, which causes inefficient combustion in the engine. The air filter can become covered with dust, grass clippings, and other particles that build up and prevent smooth airflow.


Remove the air filter completely and thoroughly clean it by tapping the filter to shake out any dirt or debris built up on the surface. You can also try blowing compressed air onto the filter to dislodge particles. If the filter is excessively dirty or clogged, replace it with a new air filter. Make sure to reinstall the cleaned or replaced air filter properly, seating it firmly in the air filter housing. This allows the proper amount of airflow to the carburetor so it can mix the air and fuel in the optimum ratio for smooth engine operation.

Bad Fuel 


Using old, stale gasoline that has deteriorated over time can be a great cause of cutting problems, as it loses its volatility and does not vaporize well in the carburetor to mix properly with air. Dirt or water contamination in the gasoline can also lead to particle blockages in fuel delivery passages, causing insufficient fuel delivery and sputtering.


First, you need to drain all of the old gasoline from the mower’s fuel tank and dispose of it properly, then replace it with fresh, high-quality gasoline. If you need to store fuel for over 30 days, use a fuel stabilizer additive like Sta-Bil to prevent deterioration. Check the fuel tank for any water or dirt sediment accumulation and drain it out. Replace the fuel filter if it appears dirty or clogged from contaminants. Adding a fuel injector cleaner like Seafoam can also help clean out any residues from old gas in the carburetor.

Spark Plug Issues


Faulty or improperly gapped spark plugs can also cause engine sputtering. Worn spark plugs may misfire while an incorrect plug gap leads to uneven ignition timing. Carbon deposits that build up on the plugs from rich fuel mixture or oil leakage can also reduce sparking. 


Thoroughly inspect the spark plugs and replace them if the electrodes are worn or if there is heavy carbon fouling present. Use a spark plug gap tool to check the gap against manufacturer specifications and adjust if needed. Be sure you replace it with the specified spark plug type. For carbon-fouled plugs, try cleaning the buildup off with a wire brush before replacing them. Also, consider replacing worn spark plug wires and inspecting the distributor cap and rotor for any cracks that could cause misfires.

Carburetor Problems Leading to a Sputtering Lawn Mower


Issues like a stuck float needle, improperly adjusted carburetor screws, and varnish or dirt buildup in the carburetor jets and passages affect proper fuel delivery and cause engine sputtering.

Riding Lawn Mower Sputtering: Carburetor Problems


Clean your carburetor thoroughly by spraying cleaner into the jets and passages to remove any accumulated debris or varnish. Make adjustments to the screw settings based on manufacturer specifications. If cleaning does not resolve the sputtering issue, a full rebuild or replacement may be necessary. Using a fuel stabilizer additive when storing the mower can help prevent carburetor varnishing. For more details, check out my post on carburetor cleaning by clicking here.

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Fuel Line Issues


Blocked fuel lines and filters prevent adequate fuel flow to the carburetor, potentially causing sputtering. Kinks, cracks, blockages from dirt buildup, and general degradation of the lines over time can all restrict proper fuel delivery.  


To resolve it, first carefully inspect the fuel lines and filters for any kinks, cracks, clogs, or other degradation and clean out or replace the lines and filters as needed. Then install an inline fuel filter if there currently isn’t one. When replacing degraded rubber fuel lines, use an approved plastic fuel line. Make sure the fuel tank vent cap is clear of debris to maintain proper fuel tank pressure. Proper fuel flow and delivery are restored by addressing any fuel line issues.

Water in Fuel


Water that has condensed in the gas tank or contaminated the gasoline will cause the lawnmower to leave strips and sputter. The water displaces the fuel delivery and small droplets can stall out combustion when they reach the cylinders. Even a small amount of water causes issues.


Drain the entire fuel tank of old gasoline completely, dispose of it properly, and remove any water or debris stuck in the bottom of the tank. Refill with fresh high-quality gasoline, considering adding fuel stabilizer to prevent condensation issues. Inspect the fuel tank cap vent for any damage or clogs that could be allowing moisture inside. Check fuel filters for any water accumulation and proper filtration. Adding an inline fuel filter can provide additional filtration to catch water before it reaches the carburetor.

Ignition System Troubles


Problems like worn-out spark plug wires, cracked distributor caps, faulty ignition coils, or loose connections anywhere in the ignition system can lead to misfires and engine sputtering. Lack of sufficient spark prevents proper air-fuel combustion in the cylinders.


Thoroughly inspect spark plug wires, distributor cap, ignition coil, and all connections for damage, cracks, or looseness, and repair or replace any worn ignition components. Make sure all ignition system wires are properly routed to avoid crosstalk or interference leading to misfires. Verify that the spark plug wires are connected in the correct firing order. Tightening down any loose connector screws and wire clamps can help improve contact. Overall ignition system maintenance and connection integrity are key to smooth running.

Low Oil Level


Running the mower engine with an oil level that has dropped below the full mark can cause sputtering issues. Insufficient oil leads to increased mechanical friction and wear in the engine and reduces cooling capability leading to overheating.


Check the engine oil level regularly before operating the mower, and refill the oil to the proper level if it is low based on the owner’s manual specifications. Look for any oil leaks that may need to be repaired to prevent the loss of oil over time. Change the oil on a regular basis, as old, dirty oil loses its lubrication properties. If the engine has been damaged from running while low on oil, you may need to have an engine repair specialist assess it and perform an overhaul if needed. Proper oil levels prevent many issues.

What to do if the Lawn Mower is still Sputtering?

You’ve taken care of your mower with the above fixes, but the sputtering issue just won’t go away. We’re here to help, so don’t worry. We won’t quit until your mower is purring like a kitten.

Start by giving the exhaust a close inspection. It may occasionally become clogged with grass or other debris, resulting in poor airflow. If you notice any obstructions, remove them to ensure efficient operation.

Now carburetor plugs. These tiny parts ensure the proper ratio of air and fuel, acting as the conductors of an orchestra. To keep that symphony playing, they should be replaced if they are worn out or damaged.

Give the spark plug wires and distributor cap a friendly inspection before moving on to the ignition system. We want those sparks to be reliable friends—strong and steady.

The fuel filter should not be overlooked. It may eventually become clogged, causing your fuel flow to become clogged. Cleaning it or replacing it can significantly alter the situation.

Although diving into the vacuum leak world might seem intimidating, doing so is similar to plugging up tiny draughts in your house. Check the connections and hoover hoses; if you discover any cracks, it’s time to make a small repair to keep everything airtight.

Now, even if your mower continues to sputter after all of this, it is still working. It involves knowing when to call in the experts. The problem can be identified and fixed by a mechanic or a lawn mower expert with the appropriate equipment and knowledge. And if it’s a lost cause, they can help you locate a new, dependable lawn care partner.

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When your riding lawn mower sputters, focus on the air filter, fuel, spark plugs, and carburetor. Clear any clogs or debris, replace faulty parts, and make tune-ups. With regular maintenance and care for these key engine components, your mower will run smoothly again, keeping your lawn neatly manicured.


How do I know if it’s the fuel system making my mower sputter?

If you’re getting black smoke or smelly fuel odors, chances are there’s a fuel delivery problem like a blocked fuel filter or carb turning sluggish.

What type of routine maintenance can help avoid sputtering problems?

Changing oil regularly, replacing air filters, using fuel stabilizers, and cleaning the carburetor can all help prevent many sputtering causes.

When should I take my sputtering mower to a professional mechanic?

If you’ve tried common solutions like checking the air filter, fuel, spark plugs, etc. and it still sputters, it likely requires a shop diagnosis and repair.

I have replaced the air filter, but it’s still sputtering.

Issues like bad gas, faulty spark plugs, and carburetor gunk could still be the culprits.

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