You’re all set for a tidy-up, pull the cord… and your mower fires up, then cuts out like it’s changed its mind. Annoying, isn’t it?
If your lawn mower starts then dies, the fix might be simpler than you think. Whether it’s a clogged carburettor, stale petrol, or a blocked vent, we’ll show you how to spot the problem and get your mower running again without the stop-start drama.
Common Reasons Why Your Lawn Mower Starts Then Dies & How to Fix Them
If your lawn mower starts and then dies, chances are it’s struggling with either fuel flow, air intake or ignition. The engine needs all three working together to keep running smoothly.
The good news? Most of these problems are easy to spot and fix with a few basic tools and a little patience.
Dirty Carburettor
The carburettor mixes air and fuel so the engine can run. Over time, old petrol can leave behind sticky deposits that block its tiny jets. When that happens, the engine may fire briefly but stall because it isn’t getting steady air & fuel supply for a proper mix.
How to fix it:
- Disconnect the spark plug to prevent accidental starting, and turn off the fuel valve (or pinch the fuel line with a clamp).
- Remove the air filter cover to expose the carburettor.
- Spray a carburettor cleaner directly into the carb throat and onto the linkages. Let it soak for at least 5 minutes.
- Use compressed air to blow through the jets and passages.
- Loosen the float bowl underneath and drain any old fuel into a container, then tighten it back up.
- If spraying alone doesn’t help, carefully remove the carb, strip it down, and soak the metal parts in carb cleaner for 15+ minutes.Rinse all parts with clean carb cleaner, dry them thoroughly, and then blow through jets with compressed air.
- Reassemble everything, reconnect the spark plug, and try starting the mower. If it still dies, the carb gaskets might need replacing.
Old or Stale Fuel
Petrol goes off surprisingly quickly, usually within 30 days. As it ages, it loses volatility and may even absorb moisture, leading to poor combustion. This is one of the most common reasons of a lawn mower that starts then dies moments later.
How to fix it:
- Drain the tank into a proper fuel container. A small siphon pump or even a turkey baster works well for this.
- Empty any stale petrol left in the carburettor bowl (see the carburettor section above).
- Refill with fresh unleaded petrol(E5 is ideal in the UK) and consider adding a fuel stabiliser if the mower will sit unused for a while.
- Start the mower and let it run for a few minutes to draw the fresh fuel through the system. If it coughs a little at first, that should clear as the old varnish burns off.
Faulty or Dirty Spark Plug
The spark plug ignites the air-fuel mixture inside your mower’s engine. If it’s fouled with carbon, has a cracked insulator, or the gap is off, it won’t deliver a strong spark. That can cause the engine to fire once, stumble and cut out.
How to fix it:
- Pull off the spark plug lead and unscrew the plug with the correct socket. Brush away any dirt around the hole before removing it.
- Check the plug carefully. If the porcelain is cracked or the tip is badly worn, replace it with a new one of the same type.
- If it looks reusable, spray it with plug cleaner and scrub the electrodes with a wire brush until they’re clean. Check the gap using a feeler gauge and adjust it to the correct setting if needed.
- Thread the plug back in by hand, then tighten with a socket (don’t overtighten). Reattach the lead and test the mower.
Blocked Fuel Cap Vent
The fuel cap does more than seal the tank; it has a tiny vent that allows air to flow in as fuel flows out. If this vent gets blocked, a vacuum forms in the tank, starving the engine of fuel. The result? Your mower runs for a few seconds and then cuts out.
How to fix it:
- Loosen the fuel cap slightly and try starting the mower. If it now runs without stalling, the vent is clogged.
- Remove the cap completely, brush off any dirt or debris, and spray carb cleaner or compressed air through the vent hole to clear it.
- Tighten the cap again and run the mower. If the problem persists, consider replacing the cap with a new vented one to avoid future issues.
Clogged Air Filter
Engines need clean air to mix with fuel for proper combustion. When the air filter gets packed with grass clippings, dust, and dirt, airflow is restricted. This causes the fuel mixture to run too rich, choking the engine and making it stall soon after starting.
How to fix it:
- Remove the air filter cover and take out the filter element.
- For a paper filter:Gently tap it on a hard surface to knock out loose debris. If it looks heavily soiled or soaked with oil, replace it with a new one.
- For a foam filter:Wash it in warm, soapy water, rinse thoroughly, and allow it to dry completely. Lightly coat it with clean engine oil before refitting.
- Reassemble and test. With the filter clean or replaced, restart the mower. The engine should now run without stalling.
Moisture or Blockage in the Fuel Line
Humid or rainy weather can cause moisture in the fuel tank or line, which can sink to the bottom and disrupt combustion, while dirt or debris can block the fuel hose and starve the engine. Either problem can cause your mower to start and then suddenly die.
How to fix it:
- Drain the tank and fuel line into an approved container. Dispose of old or contaminated fuel responsibly.
- Inspect the fuel hose. Detach it from the carburettor and blow through it to check for blockages. Replace any hose that’s brittle, cracked, or kinked.
- Replace the in-line fuel filter. A clogged filter is often the culprit and is inexpensive to swap out.
- Refill with clean, fresh petrol (consider adding a stabiliser if storing for a while) and run the mower for a few minutes to flush any remaining moisture from the system.
Clogged or Dull Mower Blades
Although the blades aren’t part of the combustion process, their condition directly affects engine strain. When grass clippings or debris clog the underside, or when blades become dull, the engine has to work harder to spin them.
This added resistance can cause the engine to overheat, stall, or shut down, especially in thick or wet grass.
How to fix it:
- Disconnect the spark plug lead for safety, then tilt the mower with the carburettor facing upwards to avoid fuel leaks.
- Clean the underside of the deck. Use a plastic scraper or putty knife to remove any built-up grass and debris.
- Inspect the blade. If the edge is blunt, nicked, or uneven, remove it and sharpen it with a file or grinder. If it’s badly damaged, fit a new blade.
- Reinstall properly. Tighten the blade bolt to the correct torque, lower the deck, and restart the mower. It should now handle grass more easily without stalling.
Preventive Maintenance Tips to Keep Your Mower Running Smoothly
The easiest way to avoid a lawn mower starting and then dying is to stay on top of basic maintenance. A little care goes a long way towards keeping your machine reliable and extending its life. Here’s how to keep things running smoothly all season:
Use Fresh, Treated Fuel
Petrol begins to oxidise and collect moisture in as little as 30 days, which leads to gum, varnish and hard starting. Always fill up with fresh unleaded petrol and consider using a fuel stabiliser if the mower will sit unused for more than a month.
Store spare fuel in an approved container and keep it in a cool, well-ventilated place away from direct sunlight or heat sources.
Check Oil, Air and Spark Regularly
Routine checks can prevent bigger problems later.
- Pull out the dipstick before each use and top up or change the oil if it’s dark or gritty.
- Inspect the air filter monthly. Replace a paper filter if it’s dirty, or wash and re-oil a foam filter.
- Remove the spark plug every season (or roughly every 25 hours of use). Clean or replace it and check the gap before refitting.
Clean the Deck After Each Mow
Grass clippings and debris collect under the deck, blocking airflow and encouraging rust. After every mow, disconnect the spark plug and tilt the mower carefully (air filter side up) to scrape away any buildup.
Keep Blades Sharp and Balanced
A sharp blade cuts cleanly and reduces engine strain. A dull one tears at the grass, leaving ragged edges and forcing the engine to work harder. Aim to sharpen your blade every 20–25 hours of mowing or at least twice per season. If it’s chipped or badly worn, fit a replacement.
End-of-Season Routine
Before putting the mower away for winter:
- Run the engine dry or fill the tank with stabilised fuel to stop varnish forming in the carburettor.
- Wipe down the body and metal parts with a light oil to prevent rust.
- Store the mower in a dry, sheltered space, well away from heaters or open flames.
When to Call a Mechanic or Replace
Sometimes even with the best care, a mower will still play up. Here’s how to know whether it’s worth fixing or time to move on:
Call a mechanic when…
- You’ve tried fresh fuel, cleaned the air filter and swapped the spark plug, but the mower still won’t stay running.
- The engine smokes heavily, knocks, or makes unusual noises—these can indicate serious internal wear.
- The starter cord is suddenly stiff or won’t pull, which might mean a bent crankshaft (often from hitting a hidden rock).
- Safety features like the blade brake or dead man’s handle have stopped working. These are essential and should be repaired professionally.
Replace the mower when…
- The mower is over 10–15 years old and showing its age.
- The deck has rust holes or cracks that affect performance and safety.
- The engine or drive system has failed and repair costs are creeping close to the price of a new machine.
- You’re considering switching to an electric, battery-powered, or even a robot mower for easier upkeep or to meet local noise/emissions rules.
Are robotic lawn mowers any good?
Robot lawn mowers aren’t just for gadget enthusiasts anymore; they’ve become a smart, time-saving solution for gardens of all sizes. Unlike traditional mowers, they trim the grass little and often, keeping your lawn neat and healthy without you lifting a finger.
Because they run on rechargeable batteries, there’s no need to worry about fuel, oil changes or noisy engines. They’re also far quieter than petrol mowers—many models hum along at around 56 dB, quieter than a normal conversation—so they can even run at night without disturbing you or the neighbours.
If you’re ready to retire the push-along, the eufy Robot Lawn Mower E15 is a strong candidate for smaller UK gardens. Its headline trick is true wire-free installation: dual 3D stereo cameras and eufy’s V-FSD vision system map your lawn in real time, so there’s no need to bury a perimeter wire or set up an RTK base. A one-tap mapping routine in the app defines virtual boundaries and multi-zone pathways for front, back or side lawns.
Despite its compact size, the E15 can handle lawns up to 800 m² (0.2 acres), which covers most suburban plots. It offers adjustable cutting heights from 25 mm to 75 mm, uses an 8-inch (203 mm) cutting deck, and can tackle slopes up to 18° (around a 40% incline). The mower runs at a quiet 56 dB, so you won’t even notice it working, and with an IPX6 water-resistance rating, you can hose it down after a muddy session without worry.
A full charge takes about 90–110 minutes, and if the battery runs low mid-mow, it automatically returns to its charging dock and resumes where it left off. The E15 also comes with built-in safety and security features, including real-time obstacle detection to steer around pets and toys, GPS tracking for anti-theft protection, and over-the-air software updates that keep its navigation improving over time. It even includes an edge-trimming mode to tidy up borders, so you’ll spend less time strimming.
Conclusion
A lawn mower starts then dies can be a real headache, but as you’ve seen, most fixes are straightforward with a little know-how. By keeping up with basic maintenance and addressing small issues early, you’ll save time, money, and stress in the long run.
Still cutting out after all that? It might be worth booking a service or, if your mower’s seen better days, upgrading to something more reliable, or even a smart robot mower like the eufy E15. Either way, don’t let mower troubles put your garden plans on hold this summer.
FAQs
Why does my lawn mower only run for a few seconds then dies?
This usually means the engine gets just enough fuel or air to start, but not enough to keep running. Common causes include a dirty carburettor, stale fuel, a clogged air filter, a blocked fuel cap vent, or a faulty spark plug.
How do you fix a lawn mower that won’t stay running?
A lawn mower that won’t stay running may have issues like a faulty spark plug, dirty carburettor, or old fuel. Start by inspecting and cleaning or replacing the spark plug. Clean the carburettor to remove any blockages, and replace any old fuel with fresh gasoline. Additionally, check the air filter for clogs and replace it if necessary.
Why is my lawn mower starting but not staying on?
Your mower may start briefly but shut off due to poor fuel or air flow. Likely culprits include a dirty carburettor, stale gas, a clogged air filter, or a blocked fuel cap vent. In some cases, clogged blades or a strained engine also contribute.
Related Blogs
Check out these articles for more information:
