Lawnmower sputters when blades are engaged, the causes and fixes


Do you have a lawnmower that is sputtering as soon as you engage the blades? Sputtering noises may seem very uncomfortable, especially if you maintain your machine well. There are many different reasons for the engine sputtering. Damaged drive belts, dirty pulleys, or faulty safety switches can lead to this problem. If the engine’s air and fuel supply is not working correctly, it can cause the engine to have less power and be a reason for the sputtering sounds. This article lists the possible remedies that will help fix the issue and make your machine work well again.

Lawnmower sputters when blades are engaged, the causes and fixes:

  1. Check the fuel
  2. Check the air filters
  3. Check the fuel filter
  4. Check and fix the venting of the gas cap
  5. Clean and Adjust the carburetor
  6. Water in the fuel line
  7. Repair or replace damaged spark plugs
  8. Sputtering when mowing long grass
Lawnmower sputters when blades are engaged, the causes and fixes 1
(CC BY 2.0) by Tim Pierce

In most cases, the problem can be fixed by yourself without much trouble. If you see that the damage seems beyond your expertise, it can be a good idea to consult a professional.

This blog post gives you a step-by-step explanation for all the causes and fixes to quickly solve the sputtering problem.

Troubleshooting steps to fix a sputtering lawnmower:

To fix your sputtering lawnmower, first, check and identify the cause that leads the mower to sputter. Many general causes can lead to sputtering. These reasons include dirty carburetor, old or stale fuel used, clogged or dirty air filters, water in the fuel tank, and many others.  We will guide you through the different causes and explain how to fix them:

● 1. Check the fuel

Gas from the local gas station comprises ten percent of ethanol, which works very well for cars, but it is low quality. It is capable of melting plastic parts, which can cause sputtering. If it is kept in the garage for more than two months, it will worsen and lead a lawnmower to sputter.

Adding fuel stabilizers can make your gas last longer. Another solution is to use ethanol-free gas. A pricey fuel may help the mower to work much better than the old and cheaper fuel. Avoid using substandard gas for your lawnmower and notice the change in performance.

● 2. Check the Air filter

A dirty air filter can disturb the fuel flow to the combustion chamber. This will result in your engine having less power and can make it sounds rough. The problem can also result in the engine starting to sputter when blades are engaged. At that time, the engine needs more power to get the blades rotating.

Fix: To fix this problem, clear the air filters or replace them. Foam air filters can be cleaned easily with some warm water and a drop of dishwasher soap. Paper air filters should be changed or replaced. Wipe away the debris and dirt from the housing if you notice this.

● 3. Check the fuel filter

Another big reason for the engine to have less power is a dirty fuel filter. The mower may run rough because it does not have the correct balance of air and fuel and can cause the mower to sputter.

Fix: To fix the problem, you have to locate the fuel valve and turn it off. If there is not fuel valve, empty the fuel tank. Empty the fuel line after disconnecting it from the carburetor. Use a flashlight to check for holes, dirt, and debris in the fuel line. Use a fuel cleaner to clean the dirty fuel line. If that does not help, you have to replace the fuel line. Check the filters and vents for any dirt and debris and clean if needed.

● 4. Check the venting of the gas cap

Improper venting of the gas cap increases the vapor lock risk as not enough air can enter the gas tank.

Fix: To tackle this issue, remove the cap and check if the vent hole is still open. If that is not the case, try to clean it. Check again if you can blow some air through it. If you do not manage to clean it, replace it.

● 5. Check and adjust the carburetor

If the air filter and fuel filter are clean, the sputtering is due to a carburetor problem.

mower is sputtering due to the dirty carburetor. It is easy to tune-up or repairs the carburetor, and it involves only a few simple steps. If you monthly or seasonally follow through with these steps, you will enjoy long-term use of a mower and protect it from severe impairment or damage.

Fix: The most straightforward carburetor fix is to use carburetor cleaning spray. If that does not work, you have to remove the carburetor and clean it. If the carburetor is clean, it is also possible that your carburetor is not adjusted correctly. The engine needs the right amount of air and fuel mix to perform well. Over time it is possible that the adjustment is off and needs to be corrected. If all failed, and you tried everything related to this, it can be a good idea to consult a professional for this.

● 6. Water in the fuel line

If you spot water in the fuel line, this can prevent the gas-air mixture in the cylinder from proper ignition. Condensation in the gas tank can be the reason why the gas becomes contaminated with water. As water is denser than the gas, it will be collected at the fuel tank’s bottom. This water will then be sucked into the fuel lines.

Fix: Drain the water from the fuel tank, fuel line, and carburetor. Then add new gas.

● 7. Repair damaged spark plugs

Damaged or worn spark plugs can be a reason for engine problems. It is not the most common cause that lawnmowers sputter, but it is easy and worthwhile to check. Make it part of your lawnmowers’ annual maintenance to mitigate the risk of sputtering due to a badly working spark plug.

Fix: Remove the sparkplugs and check them. Use a sparkplug tester if you are not sure about the condition. Clean any dirt from the tip with a metal brush. Replace if needed.

● 8. Sputtering when mowing long grass

Mowing tall and wet grass can also make your mower sputter. Also, in this case, the engine needs to deliver more power than usual. Check the lawn mower’s bottom if there is any caked grass or dirt on the mower’s deck.

Fix: The first step is to remove the grass from the inside of the mower deck. Then set the lawnmower on a higher level so you do not cut as much grass. If the grass has been cut to this new height, you can lower the mower and cut it to this lower height. Another method is to go slower and only cut half of the width of your mower deck. So half is cut, the other half is going over already cut grass. This way, you ask less from your engine.

● 9. Ask a Professional for help

In case the sputtering problem persists after you followed the different steps, it can be time to ask a professional for help.

Safety measures:

Safety should always be your primary concern whenever carrying out repair work of any kind.

1. Unintentional starting: When working on the engine, always disconnect the sparkplug cables. This way, the engine can not start unintentionally. In case of an electric lawnmower, remove the batteries or disconnect the wall plug.

2. Keep away from Children: Each year, many children and adults get hurt during mowing or working on lawnmowers. Ensure that they are kept away from children when you are working on your mower. Rotating engine parts can be hazardous. And small stones or other debris can escape during mower and be thrown in the air.

3. Working with gas: As you know, fuel is easy to ignite. Always make sure that when you are working with gas, there is nothing to ignite it. Additional fuel contains different chemicals that can harm your eyes, so wear some eye protection.

Frequently Asked Questions

1. Why is the lawnmower running rough?

Make sure the fuel filter is cleaned or replace when needed. If you have a clogged fuel filter, there will not be sufficient gas getting continuously to the engine. Another reason can be bad gasoline that gives rise to the same problem by affecting carburetor. It gums up the carburetor and leads the lawnmower to run rough. Also, check for the intake pipelines that are used to get the air to the carburetor. It may be clogged as well.

2. What is the reason that causes the lawnmower to keep cutting out?

A spark plug problem can be the cause of your lawnmower keeps cutting out. Remove the spark plugs and check them. Clean off any debris and filth with a metal brush. If needed, replace the spark plugs. If you notice that the spark plug is used, tighten it up. Another reason for your lawnmower to keep cutting out can be a dirty air filter. Check, clean, and replace if needed. Check if the fuel is reaching the engine by tapping on the carburetor’s side to aid gas flow.

3. What is the cause of vapor lock in lawnmowers?

Vapor lock is usually caused when the gasoline starts vaporizing too fast, and an excess amount of gas bubbles are present. This prevents the expected fuel delivery to the engine. A vapor lock in the pipelines can damage the internal part and cause significant damage to the combustion chamber or carburetor. Check the gas cap if the hole init is still open.

Final remarks

It is crucial to perform give your regular lawnmower maintenance. Lack of care may worsen its condition and can be the reason for many problems like sputtering. In case your machine has this problem, there are several steps that you can follow to fix it. The main cause is the engine not having enough power. When you do not manage to fix it, it is better to ask a professional for some assistance.

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