Lawn mower is surging is a serious concern and it could happen due to a dirty air filter, bad spark plug and bad gas, etc. Do not worry because you are not alone – this problem is very common for every lawn mower owner. 

Lawn Mower Is Surging

This usually happens because your lawn mower is lacking in fuel due to the accumulation of debris, dirt, or water that has clogged the fuel lines. However, there are other potential reasons that we have to look at too, so stay tuned!

Why Is Your Lawn Mower Surging?

Your lawn mower may be surging due to any of the following: dirty air filter, bad gasoline, dirty fuel filter, blocked gas cap vent, and dirty carburetor jet. A lawn mower that surges is an inconvenience, but recognizing what the problem is will help you fix it.

Let’s tackle these possible reasons causing your lawn mower’s trouble. We will discuss these reasons one by one so you can easily identify what part of your lawn mower specifically needs repair.

1. A Dirty Air Filter

Your lawn mower has an air filter that prevents dirt and debris from entering the engine through the carburetor. This is important because having a dirty carburetor will result in the reduction of airflow into it. This will change the mix ratio of air and fuel, which causes the surging.

2. Spark Plug Bad

Another common problem that results in your lawn mower surging is a bad spark plug. A bad spark plug produces an irregular spark. The spark that should be consistent works on and off, which results in bursts of combustion that make your lawn mower surge.

3. Bad Gas to Blame

One symptom of having bad gas is surging. The quality of the fuel that you put into your lawn mower, especially if it sits there for a prolonged period of time, goes stale and will combust irregularly. This will cause the degraded performance of the lawn mower engine by clogging up the carburetor.

Reasons Lawn Mower Is Surging

4. A Dirty Fuel Filter

The fuel filter screens out contaminants from the fuel. These contaminants include dirt, dust, debris, and rust particles. When this filter is dirty, it mainly affects the flow of fuel to the carburetor. The pressure from the fuel and the irregular flow will cause the fluctuating revving of the lawn mower engine.

5. Gas Cap Vent is Blocked

The gas cap vent appears as a tiny vent in the fuel filler caps that allows the fuel inside the tank to maintain the right vacuum and pressure. However, if it is filled with dirt, pressure-related issues might come up.

Having the wrong back pressure could push or pull the fuel to the carburetor, and this caused an engine surge. However tiny, this vent serves a significant role and should thus be kept well-maintained and not be ignored.

6. Carburetor Gasket Leak

Using gaskets, the carburetors are attached to the lawn mower engine. Once these gaskets fail, the combustion chamber can pull out more air, which changes the mix ratio and leads to the lawn mower engine surging.

7. Dirty or Blocked Carburetor Jet

Inside the carburetor, you can see that it consists of small jets where fuel passes through under pressure and turns into a vapor that mixes with air and goes through the combustion chamber. These small jets can easily be blocked by any debris or dirt, resulting in your lawn mower engine surging.

How To Fix A Lawn Mower Surging?

To fix a lawn mower that is surging you can clean dirt and dust, unclog debris and contaminants, and replace some parts that are worn out.

We can relate to how frustrated you may be feeling, however, there are quick and easy ways for you to fix the problems.

1. Clean the Air Filter

Cleaning the dirty air filter will help your lawn mower perform better. Do this by removing the air filter cover first using a screwdriver. Get the filter from the housing, and set it aside. Using a cleaning rag, clean the inside of the housing.

Make sure to remove all the dirt, such as fuel residue, oil, and dirt. Get the filter, and clean it using an air-line from your compressor. It is recommended to use a new filter if you don’t have a compressor.

Holding the new or newly cleaned filter, carefully and properly place it back into the housing. After doing that, put the air filter cover back and secure the screw fixing. You can now test your lawn mower and observe its performance. You should notice the improvement in your lawn mower with a newly cleaned filter.

2. Change the Spark Plug

Replacing your spark plug can stop the engine surging of your lawn mower. As you replace the spark plug, check the gap between the coil and electrode, and look for any indications of deterioration on the electrodes. If it is already worn out, here’s how you should replace it.

Solutions Lawn Mower Is Surging

The first thing you have to do is remove the ignition cable that is connected to the spark plug. Using a plug socket or a plug wrench, remove the spark plug. You can now install the new spark plug in the engine head.

Once it is finger tight, you can get a tool to help tighten it even more, but make sure not to make it too tight. After that, you can attach the ignition cable and see an improvement as you test it.

After you have replaced the spark plug, your lawn mower should not be surging, but if it does, you should check the engine to see if there are any other problems before making further repairs.

3. Remove Bad Gasoline

Inspect your mower, and get rid of the stale gas to prevent your lawn mower from surging. Compare the color and clarity of the fresh gas to your mower gas. From there, you can tell if your mower gas has degraded in quality and needs immediate replacement.

To remove the bad gasoline, you will need a gas can, which you can use to fill with the stale gas, and a pump or siphon to pump the stale gas away from the fuel tank.

Using the gas can, place it near your lawn mower so you can easily transfer the stale gas to it. Remove the fuel cap, and position the inflow end of the pump into the fuel tank and the outflow end on the gas can.

If everything is in place, start pumping until all the stale gas transfers to the gas can. After that, you can refill your fuel tank with fresh fuel and take it for a test. Make sure you use fresh fuel every now and then to prevent surging.

4. Clean or Replace the Fuel Filter

Determine first if the gas filter is dirty or blocked by removing the nozzle from the gas tank and using a flashlight, see if there is any dirt or contaminant blocking the way. If there is, then clean out all the dirt before putting it all back together again.

If your lawn mower still surges after cleaning the fuel filter, then it is now time for you to replace it. Here’s a step-by-step guide for the procedure.

First, prepare a few tools and a new filter, and begin by removing the ignition cable and setting it aside. Switch off the fuel, and remove the spring clips holding the fuel line to the fuel filter using a pair of pliers.

Try twisting while pulling the fuel lines from the filter to disconnect it easily. Get the new filter, and secure it to the fuel lines properly. Follow the arrow that shows the direction of the fuel to make sure it flows in one direction.

After successfully replacing the fuel filter, you can now reinstall the spring clips and check if they are tightly positioned. Finally, switch the gas back on, and start your lawn mower to see if there is any improvement.

5. Clean the Gas Cap Vent

If you notice that there is dirt accumulated on the gas cap vent, start by removing the gas cap and locating the vent hole. Clean the debris that is blocking the vent hole by poking it out using a pin or a needle.

A sewing needle is recommended to easily clear out the dirt. Once finished, you can put the gas cap vent back on the tank and you should no longer experience a lawn mower surge.

6. Fixing Carburetor Gasket Leak

You can immediately fix the carburetor gasket leak by using an engine starter spray. Check first if the carburetor is firmly attached to the engine, and while it is running, start spraying the engine starter on the gaskets. You can hear a change in surging because the engine spray replaces the air with a combustible substance.

7. Clean and Unclog Carburetor Jet

Follow the following steps to clean and unclog the carburetor jet:

  • Clear out surging by cleaning and unclogging the carburetor jet of your lawn mower. Begin by removing the spark plug and the ignition cable, and set them aside to prevent mishaps from occurring. Next, switch off the fuel flow using the fuel cut-off valve. Then, remove the air filter cover and the air filter using a screwdriver. After that, remove the air filter backplate mounting bolt using a socket wrench.
  • Once you have done this, the carburetor and back plate will detach from the lawn mower. So, carefully remove the air filter back plate and the breather pipe from the crank. Using a set of pliers, detach the spring clip that grips the pipe in its position and removes the pipe.
  • In between the carburetor and air filter housing, you can see a gasket that can be easily lifted off. Get it and set it aside. From there, you can remove the fuel line from the carburetor by disconnecting the spring clips again. After doing that, you can see a throttle linkage and spring from the governor, which holds the carburetor to the lawn mower. Lift it up using your hands.Why Lawn Mower Is Surging
  • Holding the carburetor, you can now clean it using a can of rust remover like WD-40, an old toothbrush, and a cleaning rag. After giving the carburetor a good cleaning, you can remove the fuel cup on the bottom of the carburetor using a socket wrench to remove the bolt. Once the bolt is removed, it will be detached from the carb.
  • You will see the carb float after you remove the carburetor’s fuel cap. It looks like a white piece of plastic that can be found inside the cap. Using a pair of needle nose pliers, detach the float that you see, and set it aside. Now, you can remove and clean the jet, as well as the inside of the carburetor. Then, install everything back properly. Test your lawn mower, and you should see obvious improvements. However, if you don’t want to go through these tiresome procedures, you can replace your carburetor instead.


Identifying the possible reasons for your lawn mower surging and knowing how to deal with them using the right procedure are an important part of being a lawn mower owner. Let’s sum up what we have learned:

  • Lawn mower surging is a result of either bad gas or spark plug, dirty air filter, or clogged gas cap vent.
  • A dirty carburetor jet and fuel filter might also be the reason.
  • You can also consider a carburetor gasket leak, which can be fixed by an engine starter spray.

Your lawn mower surging can basically be an easy fix by replacing, cleaning, and unclogging problematic parts. Honestly, it is identifying which part has a problem that makes it hard. However, once you know the root of the problem, you can easily handle it.

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