How Do You Fix a Petrol Lawnmower That Won’t Start

How to Fix a Petrol Lawnmower that Won't StartA petrol powered lawnmower brings many benefits over its electric and manual counterparts, which is why they remain a popular choice amongst many home owners. However, as with all appliances, from time-to-time the petrol lawnmower can throw a few spanners into the works and not start at the first time of asking – which can be frustrating.

At BuySpares, whilst we know there are a few reasons why your petrol lawnmower may not work, we also appreciate that there are usually three common reasons why the lawnmower hasn’t started; and these are problems with the:

  • Fuel
  • Spark Plugs
  • Carburettor

To help you diagnose the fault and repair it, at a cheaper cost than purchasing a new lawnmower, we’ve provided this handy guide.


Nowadays most petrol lawnmowers work using unleaded petrol. Unfortunately, a downside of such fuel is that over time is can degrade and become stale, preventing your mower from starting.

Ideally, this shouldn’t be the case during the final cut of the season, but can be a common fault at the start of the cutting season in spring; but fixing the fault is straightforward and requires little more than a bucket and fresh unleaded petrol.

The first step is to drain the existing petrol within your mower into the bucket, by uncapping the fuel reservoir and emptying the fuel into the bucket. Once the fuel reservoir is empty, you’ll notice that there is a release valve on the carburettor – release the valve and drain any petrol stored within the carburettor.

Once the old petrol is drained, give the fuel reservoir a quick clean with a paper towel, before refilling with new fuel.

NB: Remember, when storing the lawnmower away for a sustained period of time, to drain any existing fuel, preventing it from going stale and preventing the lawnmower from starting.

Spark Plugs:

A little known fact is that the life of a spark plug is only 150 hours; so if you’ve had your lawnmower for a number of years and haven’t had to change the lawnmower spark plugs before, there’s a high probability that the spark plugs are the reason behind your lawnmower failing to start.

Changing the spark plugs on your lawnmower is a quick two minute job, and requires a socket to unscrew the existing spark plugs. With these removed, you may have notice some soot and carbon on the electrodes, this is to be expected over the life of the spark plug; but it’s also a sign that they need to be replaced – especially as such dirt will be preventing a spark from appearing.

With the old spark plugs out, fit the new ones and tighten using the socket set, although take care not to tighten them too much.


So your fuel is fresh, your spark plugs are fine; the last thing is to check your lawnmower carburettor. Before checking the carburettor, drain the petrol from the fuel reserve and the carburettor following the guidance above.

Once the fuel is drained from your carburettor, use a paper towel to soak up any remaining fuel before moving the fuel line out of the way.

Fuel drained and fuel line out of the way; open the nut at the bottom and remove the bottom screw so that the float chamber comes away. Once the fuel chamber has come away from the carburettor give everything a thorough clean, using compressed air clean any debris out of the pistons.

Once the carburettor is thoroughly cleaned and put back together, and fuel added, your lawnmower should start first time, enabling you to give your lawn the much needed cut and bringing your garden back into shape.

If you’ve found that these three steps haven’t helped to get your petrol lawnmower back working, don’t worry, our advice centre may have the answer – and if not, why not get in touch with us either via the comments below, or via our social platforms, and we’ll try and help!

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