What to do when a Petrol Lawnmower Won’t Start

The grass grows long and you know it is time to mow, so you get yourself ready for the task, and… the lawnmower won’t start! 

At Allans Gardeners, we know of many reasons a petrol lawnmower cannot start and most of them are easy to resolve. Read on to find out why your own petrol mower won’t start and what advice we have on a fix. 

Petrol Lawnmower Maintenance & Storage

Before we get into the specifics of how to deal with a petrol lawnmower that will not start, let us look at a few measures that reduce the risk of it happening. Prevention is better than cure, as they say. 

Your lawnmower is likely to remain dormant for most of the winter, but there are several things you should do to ensure it is ready to operate as soon as the weather warms up. 

  • The first step is to clean and dry the lawnmower thoroughly.
  • Do not rush this job and ensure all areas are free from debris, clean, and dry. 
  • Next, you want to drain the fuel.
  • Empty the tank completely so you might need to siphon the last bit out or disconnect the fuel line and drain the last few drops.
  • Leaving fuel in to become stale is asking for problems. 
  • Disconnect the spark plug leads for safety.
  • Store the lawnmower in a dry and safe area that is out of the way. 

Read the Petrol Lawnmower Manual

Yes, we know very few people do this, but with a lawnmower it is important. It is worth investing a bit of time reading the manual to become familiar with the safe and correct operation of your lawnmower on your way to achieving professional garden maintenance

Troubleshooting a Lawnmower Doesn’t Start

Whether the lawnmower has been idle for a week or a few months, here are the key problems to look for and how to fix. 

1. Check for Fuel Issues

The first thing to make sure of is that there is petrol in the tank. It should be fresh petrol, not stale old petrol from last season. We recommend that fuel that has been in the tank for more than a month is drained and replaced for best performance. 

To check the fuel level, unless your lawnmower has a fuel indicator, simply remove the petrol cap and give the machine a gentle shake. You should hear the petrol swishing around in the tank. Top up if necessary. 

Older lawnmowers will have a fuel tap. Ensure the tap is on. 

If you find you are having fuel issues, you could add a fuel stabilizer to the petrol. This will reduce carburetor build-up and minimize clogging. 

And, just to be sure, confirm that you use the right type of fuel. Water in the fuel tank will also cause problems. 

2. Use the Choke or Primer

The choke is used to help start the engine, particularly a cold engine. Pull it out, start, and push back in once, running smoothly. Leaving it on could cause the engine to flood. 

Newer lawnmower models have a primer instead of a choke. This needs to be pushed a couple of times before a cold start. Do not overdo it as the engine could become flooded. 

3. Check Engine Oil

This is unlikely to prevent a lawnmower from starting but low oil levels or old poor oil will do serious damage. You must keep an eye on oil. 

This is rather easy.

Most lawnmowers have a dipstick. Simply remove it, wipe it clean, and place it back in the oil reservoir. Remove it again and observe the oil level.

Top up if necessary. 

Keep a rough record of how long the lawnmower operated and refer to the owner’s manual or website for recommended oil change intervals. 

4. Inspect Spark Plugs

Spark plugs are a common cause of a petrol lawnmower not starting. To inspect the spark plug, you need to:

  • Lift and remove the spark plug lead and carefully remove using a spark plug spanner/socket.
  • Look at the end to see if it is wet from the petrol. If not, there might be a carburetor blockage.
  • Check that the fuel line is clear by removing and blowing through it. If that is fine and the plug is dry, the carb is likely the issue. 
  • Clean the carburetor if you have the experience and know-how. Alternatively, take it to a professional. 
  • If the plug is wet, the problem lies elsewhere. Look at the condition of the plug. If it is corroded, burned, or covered in sludge, you could clean it but it is probably best to replace the plug. 
  • To clean, use a grease cleaning solution or solvent and you can also give the contacts a gentle sanding.
  • You also want to make sure the gap is set correctly, according to the user manual. 

5. Ensure the OPC is Engaged

OPC or Operator Presence Control is a safety lever that needs to be engaged to start and operate the lawnmower.

You will find the recoil starter extremely hard to pull when the OPC is not engaged and the engine will not start. 

6. Check for Blade Issues

If the blades are jammed or obstructed, the lawnmower will not gain enough momentum to get going. Check for any blockages around the blades. 

7. Inspect the Air Filter

Blockages, dirt, and oil in the air filter can prevent the engine from starting. A clean filter is essential for the smooth operation of the lawnmower. It is worth checking the filter and cleaning if possible or (preferably) replacing if necessary. 

8. Survey the Ignition System

A faulty ignition is slightly more difficult to diagnose. You will need an inline spark tester. The alligator clip attaches to the muffler and the other side to the wire on the spark plug. 

To test, try to start the lawnmower and look for a spark. If there is no spark, the issue is most likely related to the ignition and will probably need a look by a professional. 

Another way to check the ignition and spark plug is to remove the lead and the spark plug. Then connect the spark plug to the lead and place the end against a metal surface. Pull the cord to see if it sparks. This will help to troubleshoot the source of the problem. 

9. Check all Cables

Another thing to do is to check that all cables are connected and in good condition. Cables can deteriorate or disconnect over time, and this will cause problems starting and running your lawnmower. 

Final Thoughts

A lawnmower that will not start can be frustrating. Above are the most common potential causes, how to identify them, and how to fix them. This should cover most of the issues you might experience and get you mowing in no time. 

More advanced problems will probably mean a call to the manufacturer if the machine is still under warranty, or a lawnmower repair service when out of warranty. 

Remember that good maintenance and proper care will help to prevent most issues. Keep your lawnmower clean, follow basic maintenance, best-practices, and you should not have any major problems. 

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We are professionals in landscaping, lawn mowing, and garden maintenance. The gardening company delivers a wide range of services along with tips and advice.
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