Lawn Mower Sputtering: Causes + Fixes (Complete Guide)

Lawn mower sputtering refers to when your mowing machine makes a sequence of spitting sounds, in a manner to suggest it’s damaged. Lawn mower sputtering is usually one of the symptoms that your mower has a maintenance problem that needs fixing. In this guide, we go through the causes and fixes for lawn mower sputtering in detail.

What causes my lawn mower to sputter?

  1. Clogged Air Filter

If the air filter on your lawn mower is dirty and clogged, the proper flow of oxygen to the combustion chamber will most likely be compromised, consequently leading to mower sputtering.

  1. Clogged Fuel Filter

Dirty and clogged air filters also hamper the proper flow of fuel to the engine’s combustion chamber, consequently affecting the proper functioning of your mower.

  1. Faulty Spark Plug

A faulty spark plug can also hamper proper mower functioning, leading to an engine that revs up and down. You can troubleshoot for spark plug problems on your mower by examining the spark plug’s firing tip for the presence of carbon fouling, or by checking the porcelain casing for signs of cracking and chipping.

  1. Presence of Moisture in the Fuel Tank

When water accidentally finds its way into your fuel cylinder by way of a loose gas cap or condensation, it results in gasoline ignition problems, consequently leading to mower sputtering.

  • Clogged Carburetor

For a riding lawn mower, the carburetor tends to collect debris buildup left over from the combustion process. Being as its purpose is to support combustion by availing air and fuel in the right amounts, its functionality in this regard is usually hampered when this debris becomes excessive.

  • A Dirty Mower Cutting Deck

If the cutting deck of your lawn mower is clogged with grass clippings, this can also result in lawn mower sputtering. This I especially common when mowing tall or wet grass using a small engine mower.

  • Use of Old or Low-Quality Fuel

With lawn mowers, it’s preferable to use pure gasoline, as the low-quality gasoline from your neighborhood gas station contains ethanol that burns fast, potentially causing sputtering. Lawn mower sputtering is even more likely to occur if you’re using ethanol-laden gasoline that’s been sitting idle in your garage for over a month or so. While you can use a fuel stabilizer to maintain the quality of your stored, low-quality fuel, it’ still best to go with pure gasoline.

How to Fix a Sputtering Lawn Mower

  1. Fixing mower sputtering caused by a clogged air filter

If your mower’s air filter is dirty and you suspect that this is what’s causing your lawn mower to sputter, you can solve this issue by cleaning the air filter with a soap solution if it’s made of foam, or by changing the filter if it’s made of paper.

  1. Fixing mower sputtering caused by a clogged fuel filter

For sputtering caused by a clogged fuel filter, you can fix the problem by completely replacing your dirty filter.

  1. Fixing mower sputtering caused by a faulty spark plug

If carbon fouling on the firing tip is the issue, you can solve the problem by using a wire brush to clean the tip, then resetting the gap. However, if the porcelain housing is chipped, you should consider replacing the spark plug.

  1. Fixing mower sputtering caused by the presence of water in the fuel tank

If there’s moisture in your gasoline cylinder, you’ll want to empty the tank and fill it up with a fresh batch of gasoline that can support proper ignition. If the moisture presence in the gas tank was being caused by a faulty gas cap, you should also consider replacing the cap with a new one as well. This will prevent vapor lock inside the fuel cylinder in future.

  • Fixing mower sputtering caused by a clogged carburetor

If there’s buildup of debris in your carburetor causing the sputtering and backfiring of your lawn mower, consider cleaning the carburetor. However, this can be a challenging task for first-timers, since it comprises several functional components like valves, floats, springs, and jets that may all require proper cleaning. If you don’t fancy cleaning your carburetor, you can completely replace it with a new one.

  • Fixing mower sputtering caused by a dirty cutting deck

If there’s excessive grass caked on your mower’s cutting deck, consider using a paint scraper to scrape off the caked grass clippings, consequently resolving your mower sputtering issues.

  • Fixing mower sputtering caused by use of old or low-quality fuel

If old, low-quality gasoline is the problem, consider emptying your fuel tank and investing in pure gasoline that’s free of ethanol; for cleaner combustion that doesn’t lead to lawn mower sputtering.

Lawn Mower Sputters and Dies

A normally functioning lawn mower should be able to run flawlessly until you’re done with your landscaping work. Therefore, a lawn mower that sputters and dies out is usually a surefire sign of engine failure. This is because the mower’s engine is dependent on the proper functioning of several different components and ingredients, such as the damage or deficiency of one of them can result in engine failure, leading to sputtering. To correct this complex issue, you should have a mower repair professional examine your mower’s engine and undertake the necessary repairs.

Lawn mower sputters when blades are engaged

If your riding mower’s engine sputters and dies when the blades are working, the problem is most likely at the switch, belt, or pulley. Below is a general repair guide for each of these mower sections:

  1. Belt

If you mower sputters when the blades are engaged, it could be that improper belt routing is the issue. To troubleshoot for the same, follow the procedure below:

  • Remove the belt guard by lowering the deck to the smallest setting.
  • Next, detach the rear deck pins and lift the belt above the pulley.
  • Now, detach the front deck pins that support the PTO cable to access an remove the spring.
  • Now, slide the deck from beneath the lawn mower and inspect for faulty belt routing.
  • If there’s an issue with the routing, check the manufacturer’s instruction manual for guidelines on how to route and re-route the belt.
  1. Pulley

Your lawn mower’s pulleys are usually engaged by the drive belt, and are responsible for rotating the spindles. Therefore, when a given pulley is sticking and doesn’t spin properly, there’s a high chance that your mower will sputter once the blades are engaged.

To troubleshoot for the same, detach the drive belt from the pulley, then, engage the blades. Now, spin the idler pulleys by hand and check whether they turn or make a certain, low-pitched sound. If that isn’t the case, you’ll have to replace your damaged pulleys. Pulley replacement is a complex job that’s best done by a lawn mower maintenance professional.

  1. Safety Switch

Finally, if your mower is sputtering and going off when the blades are engaged, it could be that you have a faulty safety switch. The role of the safety switch is usually to shut off the mower in roll-over situations. However, if it does so when it shouldn’t, there’s definitely a problem.

To troubleshoot for safety switch issues, follow the procedure detailed below:

  • Locate the safety switch from under your riding mower seat by unbolting the seat and sliding it forward. You’ll also have to unscrew the locking tab to detach the seat from its bracket.
  • Once you access the safety switch, check for damage by physically observing it. However, switch damage may not always be visible and you may have to test it with a multi-meter. If the results are anything other than a ‘zero ohms’ reading when the switch is off, it means that your safety switch is damaged and needs to be replaced.

1 thought on “Lawn Mower Sputtering: Causes + Fixes (Complete Guide)”

  1. Joseph Ainsworth

    Right side hydrostatic motor will not turn. The left side moves under the controls and freely. The park brake cable broke at the handle. I disengaged both motors with the release levers and the right motor is still a seized. When the right hand lever is moved the motor whines as if it’s getting pilot pressure but the motor will not move.

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