How To Start A Petrol Lawnmower
Each step is shown on our own Mountfield and works on almost any other petrol mower too.
The short answer
To start a petrol lawnmower, check the oil and fuel, press the primer bulb three or four times if your mower has one, then hold the safety bar against the handle and give the pull cord one sharp, firm pull. A cold engine can take three or four pulls. If it still won't start, check for stale fuel, a dirty air filter or a loose spark plug.
Mountfield, Hyundai, Cobra or a supermarket own brand, they all start in much the same way. What catches people out is the order of the steps, and missing one is enough to leave you yanking the cord over and over with nothing happening.
We used our own Mountfield for the photos in this guide. It's a push mower with a Briggs & Stratton engine and a primer bulb, the same setup you'll find on plenty of petrol lawn mowers for home gardens. Work through the steps below in order, especially if it's your first petrol mower or it's been sat in the shed all winter.
How To Start A Petrol Lawnmower
1. Check The Oil And Petrol
A mower has no warning lights, so the fluid checks are down to you before every start. Pull out the dipstick, wipe it clean on a tissue, push it back in fully and draw it out again. The oil should sit between the minimum and maximum marks. Top it up if it's low, and change it altogether if it's more than a year old.
Fill the petrol tank while the engine is cold. Use fresh unleaded, because fuel that's spent the winter in a can or been left in a hot shed loses its strength and makes the engine much harder to start.
2. Prime The Engine
The primer bulb is a small rubber button on the side of the engine, and it's made in a bright colour so it's easy to spot. On our Mountfield it's the red one set into the air filter cover. Press it firmly three or four times to push fuel through to the carburettor.
Some petrol mowers, particularly higher-end models, don't need priming and have no bulb at all. If yours doesn't have one, skip straight to the next step.
3. Hold The Safety Bar Against The Handle
The engine won't run unless the safety bar is held in. Pull it back against the top of the handle and keep it there while you start the mower. Self-propelled models have a second lever that engages the drive, and that one stays off for now.
The bar should move freely and need no force to hold. If it feels stiff, spray a little WD-40 on the pivots and cable ends before going any further.
4. Grip And Pull The Cord
Stand square behind the mower with the safety bar held in, take hold of the starter handle and pull it sharply in one smooth movement. It's the speed of the pull that counts, as a slow, half-hearted tug won't spin the engine fast enough to fire. From cold it can take three or four pulls, but a warm engine starts on the first.
If it hasn't fired after several attempts, stop before you flood it and work through the checks further down this page.
5. Engage The Self-Propel Drive
Once the engine is running, a self-propelled mower drives itself forward when you pull the drive lever up to the handle. It powers either the front or the rear wheels and takes the effort out of pushing up slopes and across big lawns. You don't have to use it all the time, and it plays no part in starting the engine.
Why Won't My Petrol Lawnmower Start?
When a mower refuses to start after you've followed every step above, the cause is nearly always one of a handful of simple faults. Work through these checks in order:
- Fuel: The tank is low or the petrol is stale. Drain it and refill with fresh unleaded.
- Jammed blade: A cord that's very hard to pull points to grass or debris stopping the blade turning. Pull the HT lead off and clear underneath.
- Spark plug: The plug has worked loose or the HT cap isn't pushed fully home.
- Priming: On a very cold morning the engine needs a few more presses of the bulb.
- Air filter: A clogged or damaged filter starves the engine of air.
- Safety cable: If the cable from the safety bar has come loose at the engine end, the mower won't fire at all.
Most of these come down to maintenance. Our photo guide to servicing a petrol lawnmower covers the oil, filter, plug and blade in one session, and a yearly service keeps the engine starting reliably.
Pull Starting Compared With Electric Mowers
The pull cord is the part of petrol mowing some people never get on with. An electric mower starts with a button or a lever, and that's one of the trade-offs we've weighed up in our guide to choosing a petrol or electric lawn mower. If an easy start matters more to you than raw power, take a look at our pick of the best electric lawn mowers.
Once your mower is running, set the cutting height before you head onto the grass. A new lawn needs the highest setting, and our guide on cutting new grass for the first time explains why.
Quick Questions And Answers
How many times should you press the primer bulb on a lawnmower?
Press the primer bulb three or four times before starting a cold petrol lawnmower. That pushes enough fuel through to the carburettor for the engine to fire. On a very cold morning a couple of extra presses can help, but don't keep pumping it, as too much fuel floods the engine and makes it harder to start.
Why is my lawnmower pull cord hard to pull?
A lawnmower pull cord that's very hard to pull points to something stopping the blade turning. Long wet grass, a clump of packed clippings or a stick jammed under the deck are the common causes. Pull the HT lead off the spark plug, tip the mower with the air filter facing up and clear the blade before trying again.
Do you need to prime a warm petrol mower?
A petrol mower that's already warm doesn't need priming. The primer bulb is for cold starts, when the engine needs extra fuel to fire. If you've stopped partway through mowing to empty the grass box, hold the safety bar in and pull the cord, and a warm engine fires on the first pull.
What should you do if you flood a lawnmower?
If you flood a petrol lawnmower, stop pulling the cord and leave it to stand so the extra fuel can evaporate. A strong smell of petrol around the engine is the giveaway. When you try again, don't prime it. Hold the safety bar in and give the cord a few firm, steady pulls until it fires.
Do I hold the self-propel lever when starting the mower?
No, leave the drive lever alone until the engine is running. Starting only needs the safety bar held against the handle. Once the engine has fired, pull the drive lever up as well and the mower will start moving forward on its own, so make sure you're ready to walk.
What does the safety bar do on a petrol mower?
It's a dead man's switch. Let go of the bar and the engine and blade stop, which is why the mower won't run unless you're holding it against the handle. A healthy bar moves freely with no effort, so a stiff one wants a little WD-40 on the pivots and cable ends, and a cable that's come loose at the engine end stops the mower firing at all.
Does old petrol stop a mower starting?
Yes, petrol loses its strength over a winter in a can or a summer in a hot shed, and an engine running on it is much harder to start. If you suspect the fuel, drain the tank and refill it with fresh unleaded while the engine is cold. It's a good moment to pull the dipstick too, as oil more than a year old wants changing.
Is it worth switching to an electric mower to avoid the pull cord?
It depends what you value more. Electric mowers start with a button or a lever, so there's no cord to fight with, while petrol gives you more power. If easy starting wins, electric is worth the switch, and our guide to choosing a petrol or electric lawn mower sets out the other trade-offs.
Archie is our gardening specialist. He started out as an apprentice at a gardening firm, built up his own knowledge from there and now writes most of our garden content.