Why won't my lawn mower start? Common causes and simple fixes

You go to start your mower and nothing happens. Or it splutters for a second and then dies. Or it turns over but will not fire up. Sound familiar?

We get calls about this all the time, and the good news is that most starting problems have simple causes. Here are the most common reasons a mower will not start, and what you can do about it.

The fuel has gone stale

This is by far the most common problem, especially at the start of the season. Petrol deteriorates after about three months, and old fuel can clog the carburettor and prevent the engine from starting.

The fix: Drain the old fuel out and replace it with fresh petrol. If it has been sitting for a long time, you might also need to clean or replace the carburettor, but draining the fuel is always the first thing to try.

Prevention: At the end of the mowing season, either run the mower until the tank is empty or add a fuel stabiliser to keep the petrol fresh over winter.

The spark plug is dirty or worn

The spark plug ignites the fuel in the engine. If it is covered in carbon deposits, corroded, or the gap is too wide, the engine will not start.

The fix: Pull out the spark plug and have a look. If it is dirty, clean it with a wire brush or some fine sandpaper. If it looks worn or damaged, replace it. Spark plugs are cheap and easy to swap.

Prevention: Replace your spark plug once a year as part of your annual service. It is one of those small jobs that makes a big difference.

The air filter is clogged

The engine needs air to run. If the air filter is blocked with dirt and debris, the engine will struggle to start or will run very poorly.

The fix: Remove the air filter and give it a tap to knock out any loose dirt. If it is heavily clogged or damaged, replace it. Paper filters are not expensive and foam filters can be washed and reused.

Prevention: Check your air filter a few times a season and clean or replace it as needed, especially if you mow in dusty conditions.

The oil level is too low

Some modern mowers have a low-oil shutoff feature that prevents the engine from starting if the oil level is too low. This protects the engine from damage, but it can be confusing if you do not know it is there.

The fix: Check the oil level with the dipstick. If it is low, top it up with the correct grade of oil for your mower (check the manual if you are not sure). If the oil is very dirty, change it.

Prevention: Check your oil level regularly and change the oil at least once a year.

The starter cord is broken or jammed

If the starter cord will not pull, or if it pulls but does not engage the engine, there might be a problem with the recoil starter mechanism.

The fix: This one is a bit trickier to fix yourself. If the cord is frayed or broken, you can replace it, but if the recoil spring is damaged or the mechanism is jammed, it is usually easier to bring it in and let us sort it out.

The mower has been tipped on its side

If you have tipped the mower on its side to clean the underside or sharpen the blades, oil or fuel might have leaked into places it should not be. This can cause the mower to smoke, run poorly, or refuse to start.

The fix: Let the mower sit upright for a while to allow any leaked fluids to drain back to where they belong. Check the air filter and spark plug and clean them if needed. Try starting it again after 15 or 20 minutes.

Prevention: Always tip the mower so the air filter and carburettor are facing upwards, not down towards the ground.

It just needs a service

Sometimes there is no single obvious cause. The mower might just be tired, dirty, or neglected. A full service often solves starting problems by cleaning everything up, replacing worn parts, and getting the engine back to how it should be.

If you have tried the basics and your mower still will not start, or if you would rather not get your hands dirty, give us a call. We will collect it, diagnose the problem, and have it running properly again.

Call Surrey Power Machinery on 07776 210601