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Why My Lawn Mower Losing Speed? Reasons With Quick Fixes

Lawn mowers are one of the most common tools used by homeowners. It is an essential tool for their gardening needs. This is a powerful machine and is supposed to be able to handle different terrain.  

However, the more time you use it, the slower it goes. With so many different reasons why you might see your lawn mower losing its speed, knowing what to do in such cases can save your time and money.

There are several reasons why the lawn mower would lose its power over time. Sometimes there might be a problem with the gas, other times it can have an issue with the carburetor or fuel line. 

You might even need to buy an air filter for your mower but if you don’t get that fixed, your speed will continue to decrease until you’re no longer able to use your lawnmower at all.

This article will talk about the various reasons why your lawn mower might be losing its speed, with quick fixes for each reason that can help you restore it back to normal without any hassle.

Lawn mower on a lawn
Lawn mower on a lawn

The main reasons for a lawn mower to lose speed

  1. Clogged fuel line
  2. Clogged gas cap
  3. Clogged carburetor
  4. Wrong Fuel Blend
  5. Bad battery
  6. Faulty motion drive
  7. Air trapped in the transmission

1. A dirty air filter

The air filter prevents dust and debris from entering the engine, but over time it can get clogged and reduce the airflow. This can affect the performance and efficiency of your lawn mower. To solve this issue, you should check and clean or replace the air filter regularly, following the manufacturer’s instructions.

2. Clogged fuel line

A clogged fuel line causes a lawn mower to lose its speed. The engine starts hard and stalling or misfiring or randomly stalling can happen. You can also see failures in the fuel system parts.

Clogged fuel line in a lawn mower
Clogged fuel line

When you hear your lawn mower making unexpected sounds, it means that something is wrong with your engine. 

Your lawn mower might be experiencing poor performance due to low fuel pressure, clogged fuel lines, an air leak, a faulty carburetor jetting and more.

3. A dull blade

The blade of your lawn mower is responsible for cutting the grass evenly and smoothly, but it can get dull or damaged due to wear and tear or hitting rocks or other objects. A dull blade can make your lawn mower work harder and consume more fuel or battery power. To solve this issue, you should sharpen or replace the blade periodically, depending on how often you use your lawn mower and the condition of your lawn.

4. A low oil level

The oil lubricates the moving parts of your lawn mower engine and prevents overheating and friction. If the oil level is too low, your lawn mower can lose power and speed, and even damage the engine. To solve this issue, you should check and refill the oil level regularly, following the manufacturer’s recommendations for the type and amount of oil.

5. Clogged gas cap

The problem with a clogged gas cap is that air won’t be able to enter the tank, which will lead to vacuum or “vapor lock”. This stops the flow of fuel to the carburetor and prevent it from running properly. 

Faulty fuel cap or clogged gas cap of a lawn mower
Clogged gas cap

It also can cause the engine to stall. The fuel cap vent is clogged if you hear a popping sound when you try to start your engine. It’s important to check regularly.

The carburetor is responsible for regulating the flow of fuel and air into the engine. When it is clogged, it won’t start or run properly.

6. Clogged carburetor

One of the most common cause of a lawn mower losing its speed is when the carburetor gets clogged with fuel left over for a long time. Unlike cars, lawn mowers don’t have self-cleaning systems.

Their carburetors can get clogged easily when there is a lot of debris in their engines. It also can lead to engine flooding. A flooded engine will also cause your lawn mower not to work properly and lose its speed.

Inspect each source for clogs in the engine, blockage or dirt to find clogging. Fix the clogging to get your lawn mower in the right speed you want.

7. A faulty spark plug

The spark plug ignites the fuel-air mixture in the combustion chamber of your lawn mower engine, creating the power to drive the blade and wheels. If the spark plug is dirty, worn out, or damaged, it can cause misfires, poor acceleration, and loss of speed.

To solve this issue, you should inspect and clean or replace the spark plug at least once a year, or more often if you notice any signs of trouble.

Cleaning bad carburetor of a lawn mwoer
Cleaning bad carburetor

8. Wrong Fuel Blend

When a lawn mower is not running it should be easy to identify the problem. One thing that you can check is the fuel blend. This is a very common problem that many people face. It cause your riding mower to run very slow.

What appears to be wrong for the engine could be due to a faulty fuel blend. Many people don’t know how to select the proper fuel blend, so they use whatever is available. 

Different companies use different blends of fuel of the octane. Some use gasoline with alcohol. It significantly has low impact over the environment and also reduces the manufacturing cost that means low marginal cost. 

The wrong fuel blend can wreak havoc on smaller machines, but minimal effect on large vehicles.

Ethanol mixed with gasoline is a bad combination. It will cause your lawn mower to lose speed, which makes the machine more difficult to use. 

If you are using a lawn mower, it is best to use a blend of gasoline and ethanol-free gas. Ethanol-free gas has minimal effect on havoc on smaller ones like lawn mowers.

To fix the issue, change your fuel provider and follow the instruction manual to select the right fuel for your mower at the right time to get go with your mower.

9. Drive losing

Drive losing causes a lawn mower losing speed in self-drive as well as electric lawn mowers. Generally it includes problems with battery, drive belt or trapped air somewhere in the main transmission system.

10. Bad battery

A bad battery may cause a lawn mower to lose speed. A common cause of lawnmowers slowing down is due to the engine not getting enough power from their batteries. 

A faulty or weak battery can slow down the engine significantly, which will lead to this issue as well, even though it seems like an unrelated issue at first glance.

Check the battery, is it on right charge level or low. If it’s low, then try recharging. If it doesn’t hold charge for a long then it’s time to replace the battery.

11. Faulty motion drive

A motion drive belt fault or even air trapped in the transmission may also result in this problem. A simple fix is to replace the battery and check if it has been rectified.

12. Air trapped in the transmission

A lawn mower’s transmission is important to the performance of the machine. As time goes on and as more dirt is pushed through, air starts to get trapped in the transmission causing a loss in speed. 

Clean the air transmission with proper cleaning methods to get your lawn mower right back.

These are some of the most common reasons why your lawn mower might be losing speed, but there could be other factors involved depending on the type and model of your lawn mower.

If you have tried all these solutions and still notice a problem with your lawn mower speed, you should consult a professional mechanic for further diagnosis and repair.


Lawn mower motors are powered by a small engine that is capable of moving the mower along at high speed. But lawn mower losing speed is a common problem faced by many home owners. 

It usually happens when the main reason for your lawn mower to lose speed is clogging in fuel line, gas cap, carburetor or even trapped air in transmission

Often, speed loss occurs due to faulty motion drive, which makes it difficult to push the mower through thick grass.

We’ve discussed all things in this article with proper detail to give you the idea that what happens when your lawn mower losing speed. And the quick fixes about the problem. 

Follow our instructions to get fixed. If you can’t fix by yourself, then get help from professionals or contact your dealer.

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