15 Reasons Why Your Petrol Lawn Mower Keeps Cutting Out

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Why Does My Petrol Lawn Mower Keep Cutting Out

15 Reasons Why Your Petrol Lawn Mower Keeps Cutting Out

A lawn mower that keeps cutting out is immensely frustrating, but it doesn’t mean the whole machine is destined for scrap.

There are loads of potential explanations for why your lawn mower keeps cutting out, and most of these issues are relatively easy to sort out

Take a look at these 15 reasons why your petrol lawnmower keeps cutting out (and how to fix them). 

1. The Blades are Dirty


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One of the main reasons why a petrol lawn mower keeps cutting out: blades that are clogged with grass. Chances are the grass was a bit damp last time you cut it. Lawn mower blades should ideally be hosed down at the end of each mowing session. 

If your blades are looking dirty, turn off your mower and spray the blades with a strong stream of water. Ensure you remove all the grass and debris (being mindful of the blades).

If the grass is properly baked on (for example, left on the blades from the previous season), use a hard steel brush to remove it. 

READ NEXT: How to Clean a Petrol Lawn Mower

2. The Blades are Blunt


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If your lawn mower blades are worn down, they may be putting too much strain on the engine which can cause it to cut out. 

As you can imagine, blunt blades are far less efficient than sharp blades for cutting grass as well. In fact, they can actually damage your lawn because the blades of grass get ripped instead of cut. 

Sharpening lawn mower blades can be done at home. If you’re not sure the best way to do this, take a look at our informative guide to sharpening mower blades

3. The Grass is Too Wet


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Some petrol lawn mowers will cut out when they are used on wet grass. This is due to a lack of power, as wet grass is much heavier than dry. Wet grass can also stick to the blades, which puts a lot of pressure on the engine. 

If your lawn mower only seems to cut out when the grass is wet, it may be that you are asking too much of it. Try mowing the lawn again when it’s dry and see if your lawn mower will run without any problems. 

READ NEXT: The Best Lawn Mowers for Wet & Long Grass

4. The Spark Plug is Faulty


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An issue with the spark plug is one of the most common reasons for a petrol lawnmower cutting out. Even if the spark plug looks to be in good condition, it may need replacing. Your spark plug should be replaced after every 25 hours of use

If you think the problem is with your spark plug, give in a clean. If this doesn’t help, it may need replacing. New spark plugs can be purchased online and are very inexpensive. 

5. The Fuel is Stale


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If it’s your first cut of the season, or you haven’t had to mow your grass for a while, it may be that the fuel in the tank has gone stale. 

Petrol can go bad in as little as two-to-four weeks, though usually it takes about three months.If the fuel tank wasn’t drained before storage, you may find the mower struggles to start, or runs for a few minutes then cuts out. 

You’ll need to drain the stale fuel from both the carburettor and fuel tank. Undo the carburetor’s drain bolt to release any trapped fuel (place a bowl underneath to catch any liquids). Drain the fuel tank as well. The mower should now work with the addition of fresh petrol.

If it doesn’t, the stale petrol may have damaged the carburetor.  

ANSWERED: Can You Use e10 Petrol in Lawn Mowers?

6. The Carburettor is Clogged


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If your lawn mower starts but then quickly cuts out, it’s worth checking the carburettor. If this is clogged, your lawn mower’s engine won’t be able to run for long after it has been started.

Carburettor cleaners can be purchased online and used to remove dirt from your carburettor. Ensure the mower is off and empty of fuel. Unscrew the carburettor and take it apart to clean it. Work in a well ventilated area in case any residual fuel spills out. 

You should aim to clean your carburettor once a year

7. The Carburettor Needs Replacing

If you’ve tried cleaning the carburetor but the mower still won’t start easily, or is sputtering and cutting out, it may be time for a new carburettor. 

Similarly if you’re struggling to clean the carburetor, it’s best to install a new one. 

8. You’ve Overfilled the Oil


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If you were overenthusiastic when pouring oil into your lawn mower, the engine may cut out soon after it starts running. Another sign is white smoke coming from the engine. 

If you’re using a four-stroke machine: use the dipstick to check the oil level, and drain away any excess. 

If you’re using a two-stroke machine: check the oil-to-fuel ratio mix. You may need to empty out the fuel and oil and start again.

ANSWERED: What Oil to Use in a Petrol Lawn Mower

9. It Needs More Oil

If there isn’t enough oil in your petrol lawn mower, it may cut out. Check the oil level using the dipstick and add more if needed. 

If you find any issues with the quality of the oil, such as there’s water inside it, drain the oil completely and fill with fresh oil. You should aim to change the oil completely around every 50 hours or use, or once every season. 

10. The Kill Switch has Malfunctioned

Larger lawn mowers will likely have an engine kill switch. If this malfunctions, the lawn mower may shut off after running for a few seconds. 

The kill switch is usually located on the handlebar or under the seat, and will need replacing if it malfunctions.

The best way to confirm a kill switch malfunction is to take the lawn mower to be serviced and ask them to check the kill switch.

11. The Air Filter Needs Cleaning


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If your lawn mower is cutting out in long grass, the air filter might need unclogging. Long grass and debris can block the air flow to the engine, which will cause it to cut out. 

Inspect the air filter and dislodge any large pieces of dirt. Sponge air filters can be cleaned with dishwasher soap and warm water. Dry it by squeezing it between a paper towel and leaving it to air dry. 

12. The Air Filter Needs Replacing  

The air filter of a petrol mower should ideally be replaced once a year.

Air filters can be purchased online and are inexpensive. If you’ve cleaned the air filter and your lawn mower is still cutting out, it may be that it needs replacing. 

13. The Motor Has Overheated

If your engine has overheated, the lawn mower will cut out. There are a few things that can cause overheating, including: low engine oil, clogged cutting decks and cutting overly thick grass. 

Mowing your lawn in very hot weather can also increase the risk of it overheating. 

If the mower feels hot, check the aforementioned points. If it’s a hot day, consider leaving the mowing until it’s cooler.

14. It has a Defective Petrol Cap


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A defective petrol cap is a common reason for lawn mowers to start and then stop. Petrol caps have a small vent that allows air into the tank. 

If this air vent becomes blocked, the engine may cut out. Try loosening the cap then starting the mower again. If the engine stops cutting out after loosening the cap, this is a sign that the cap needs replacing. 

15. You are Overloading Your Mower


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Cutting grass that is too thick or long for your mower will cause the engine to struggle, overheat and cut out. Ensure you have the right mower for the condition of your lawn. 

If you are mowing long grass on a low cutting height, your mower may not be able to handle it. Try raising the cutting height and see if that helps. 

READ NEXT: How to Get Rid of Your Old Lawnmower


Why does my lawn mower keep cutting out? 

The most common reasons for a lawn mower cutting out are:

  • The engine overheating (due to blunt blades, lack of oil or tackling grass which is too long/dense)
  • A problem with the spark plug
  • Using stale fuel

How do I know if there’s a problem with my lawn mower’s spark plug? 

There are a few tell-tale signs that your spark plug is failing:

  • Engine sounds jittery when it’s idle
  • Engine is cutting out
  • Engine is turning over but not actually starting
  • You are using more fuel than you usually do

How often does a lawn mower’s spark plug need changing? 

For most standard lawn mowers, the spark plug should be checked or replaced once every season and replaced every 25 hours of use. This is the guideline even if you haven’t noticed any problems with your mower.

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