Dirty or clogged air filter.

One of the most overlooked items of lawnmower maintenance is changing the air filter. People will often change or at least top up their engine oil, they may even oil a sticky cable or grease a stiff wheel,  but they neglect to clean or change their air filter. 

Dirty Air Filter.

Having a dirty air filter can cause a number of problems:

  • A dirty air filter can make starting your mower harder. 
  • Not getting enough air makes the engine run rich which can foul a plug. This may stop your mower starting or can make it run unevenly, being rough in the way it runs. 
  • You can get through lots of fuel. We had one customer who said, “I don’t know what is wrong, but I get through a take of fuel every time I mow the lawn!” It was not a big lawn.
  • Reduced Horsepower. If your mower does not feel like it has the power it once had, this could indicate that your engine is not receiving all the air it needs to perform. Since it improves airflow, replacing your air filter can improve the power you get from your mower.
  • You might also hear popping sounds or see a flame coming from your exhaust. This is caused by heat in the exhaust system igniting unburnt fuel in the exhaust, not inside the engine. This is a potentially hazardous condition and needs to be, look at, right away.
  • The suction can tear a hole in the filter, allowing debris into the cylinder which can damage the inside of the cylinder and create big and expensive problems.
Clean Air Filter.

Replacing your air filter benefits the longevity of your mower and the engine performance. Engine air filters prevent harmful debris from damaging crucial components to keep the mower running smoothly. They contribute to efficiency by helping maintain the right air-to-fuel ratio, preventing the excess consumption of petrol.

Dirty air filters keep the system from getting the right amount of air or fuel and make it harder for the engine to perform its role. Having a fully-functioning engine air filter is critical to optimal mower operation.


Above is an air filter from a stone saw, and to the left is
just some of the dust that came out of it!


Replacing your air filter. 

Most mowers have a paper or foam air filter. These should be replaced regularly. On a domestic mower probably one a year. We replace air filters each time your mower is in for a service. If your mower is used commercially, you probably need to replace your air filter more often depending on the conditions it is used in.

If your air filter gets wet or oily it will clog much more quickly and really should be replaced as soon as possible. 

There are a few filters that should be oily. Some very old mowers will have an oil bath air filter. These consist of an oiled wire mesh or a wire mesh with a shallow bath or oil. These often just need a good clean with petrol and then re-oiled. (Be careful with petrol!) If they are damaged they can need replacing.

Do let us have your tips in the comments below. 

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