What Causes A Lawn Mower To Surge & Lose Power? Find Out Here!

Written By James
Updated July 7, 2021 by James

What Causes A Lawn Mower To Surge & Lose Power? Find Out Here!

Why Is My Lawnmower Surging & Losing Power?

Typically, when your mower is revving up and down in power, the mower will not turn off, but instead might lose power after each rev, this can be common when you first start up your mower, but should not be consistent as you are mowing. 

Most of the time, power surges and loss of power are caused by the flow of fuel being constricted by an issue in your mower, however, there are other common causes such as vacuum leaks, dirty carburettor gaskets, the unbalanced air-fuel ratio from a clogged filter and more. 

Figuring out why your mower is surging can be overwhelming, especially if your a beginner with these gardening machines, so we have composed a short guide below which help you troubleshoot your mower and fix it so as it can be working how it should be.

What Does a Lawnmower Sound Like When Surging 

If your lawnmower is surging then losing power then it probably sounds likes the engine is coming to full speed the slowing down due to loss of power, you might also have to stop and restart your mower if the surging gets too bad. 

Most of the time, surging will happen to your petrol mower rather than an electric one as the surge is due to an issue with fuel flow. If the fuel to air ratio is wrong in your mower, it will result in choppy running and loss of power. 

Before you even start considering any other causes for surging and loss of power in your petrol lawn mower engine, make sure the three most important components are working how they should be first; the spark plug, fresh air and fresh fuel. 

Causes Of Surging & Loss Of Power In Mowers 

From lack of fuel to stale fuel, low oil level and dirty air filter issues, you may need to troubleshoot quite a few parts of your lawn mower/equipment engine to get to the bottom of why your mower is losing power and surging. 

Some of the common causes and solutions are listed below to help you narrow down the problem. 

Perform a Vacuum Leak Check

The carburettor in your mower's engine is where the air-fuel mixture happens which is what powers your lawnmower, if the vacuum pipe has an actual leak, this could result in a loss of air or excess air which will result in the outdoor power equipment having a choppy performance. 


Checking and repairing your vacuum pipe for your lawn mower/equipment engine is pretty easy, simply inspect the vacuum hoses for any cracks, check the classic carburettor gasket and tighten all the manifold bolts and carburettor gasket joints. 

There Might Be a Faulty Spark Plug 

As we mentioned above, the spark plug is a crucial component of your mower engine model, and when this proper spark plug becomes a dirty spark plug or has a damaged spark plug wire, it can result in your engine acting irregular when switched on. 


To identify if there is an issue and you have a faulty spark plug, disconnect the plug and inspect the wires for any damage, if you spot any other issues such as an inconsistent spark plug, it might just be best to replace the whole component as they are relatively cheap anyway.

Dirty Fuel 

Believe it or not, the fuel you might have put inside of your mower could be the reason why it is surging. The fuel inside of your mower can start to deteriorate and go bad within 30 days, condensation can then build up with the gas and stop the machine from running properly. 

Therefore, you must drain your fuel after every season and add fresh when you next use it or put a fuel stabiliser in the with the fuel to preserve it for longer. 


If you think bad fuel might be the reason why your lawnmower is surging then drain the old fuel from the tank of the lawnmower and add fresh gas, turn the mower on and let it circulate.

Clean The Carburettor 

It is common for the carburettor of your lawnmower to become blocked and dirty over time, impacting the air-fuel mixture flow, resulting in the engine surging, idling and closing/opening the throttle. This cycle will repeat until the dirty carb is cleaned. 


Depending on your skill level, if you can, you could remove the carb and give it a clean yourself while checking for a leaky gasket or damaged gaskets. You can also try taking it to a professional who will clean the carb or clean it by using a carburettor spray which allows you to spray this part of the engine to unblock it without having to remove it. 

You Have a Clogged Air Filter

A blocked air filter on your lawnmower will result in the machines engine being starved of air, this will off balance the fuel to air ratio and can be the cause of the loss of power and surge effect when running your mower. 


To fix a clogged or dirty air filter, simply remove and replace it if it is a paper one, if it is a reusable filter then you can wash it and dry it before putting it back into the engine, a thin layer of oil will also stop dirt from making its way up to the carb. 

The Fuel Seal Is Blocked 

Lastly, if you have troubleshot the causes above and your mower is still surging then the fuel shut-off valve/seal might be blocked up. The small hole in this cap is responsible for the air pressure in your mower's engine. 


If the seal is blocked on the fuel cap, simply use a small piece of wire the feed through the hole and remove any blockages.

Ways To Maintain Your Mower To Prevent Surging & Power Loss 

Most of the causes as to why your mower is surging and losing power can be prevented by regular maintenance being carried out on your lawnmower. 

We have listed some steps you can implement for maintaining your mower below to ensure it works properly in the future. 

  • Drain your tank after every second cut - To stop using your mower with old fuel by accident, drain the tank after every second cut and put fresh fuel, or add a fuel stabiliser that will extend its lifespan.
  • Clean the air filter - Every time you maintain your mower you should give the air filter a clean and replace it at least once a year for proper maintenance. 
  • Check the oil level - Make sure your oil level is not too low and check its health by looking out for any discolouration. 
  • Tighten screws - Tighten any loose bolts or screws on your mower now and then, as these can often get shook loose after some time of use.
  • Replace spark plugs - After twelve months it's a good idea to replace the spark plugs on your lawnmower to avoid any start-up issues or overheating happening in your mower's engine.

Frequently Asked Questions About Lawnmowers Surging & Losing Power 

How often should I change the oil in my lawnmower?

You should aim to change the oil inside your lawnmower after every 50 hours of use, for some people this could be sooner or later, so it comes down to personal judgement too. 

Always check the oil to see if it still looks healthy if you are unsure.

Can a faulty spark plug on my lawnmower cause surging issues? 

Yes, the spark plug on your mower is essentially what allows the whole mower to start up, so when this plug is broken, it will cause surging issues and can even cut off your lawnmower's engine during use.

Why is my lawnmower losing power when it's used uphill? 

Low fuel, ignition issues and dirty blade build-ups can be the reasons for engine issues when your lawnmower is operated uphill. 

How long will a fuel stabiliser extend the life of my fuel till? 

A stabiliser could help extend the regular lifespan of your mower's fuel from 30 days to a year or even three depending on the brand. 

Final Words 

To conclude, most of the time your lawnmower will be surging and losing power if there is something from with the gas or airflow in the engine, to find out what the issue is, you can follow our troubleshooting guide above and maintain your lawnmower regularly to avoid dirt-build issues and blockages from happening in your mower's engine. 

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My father, and his father before him, and his father; for the past 3 generations, my family have always been into gardening. The green fingers is a gift passed down to me and I thoroughly enjoy it! I also have worked in the manufacturing department for Bosch and DeWalt so I like to think I know a thing or two about tools and such!
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