Your lawn mower won't start: the 8 causes we see in the workshop and how to fix them

It is the most common call the workshop gets in spring: "the mower won't start". The good news is that in more than half the cases you can sort it at home in ten minutes. These are the checks, in the order we do them ourselves.

1. Stale petrol

Cause number one. Petrol loses its properties within a month and, after a whole winter in the tank, it leaves a varnish that blocks the carburettor. If the machine has sat for months with old fuel in it, drain the tank, put fresh petrol in and try again. If it fires and then dies, the carburettor already needs attention (point 8).

2. The safety lever

It sounds obvious, but it happens: the mower will not start unless the engine brake lever is held against the handlebar. If the cable has stretched over the years, the lever no longer releases the brake and the engine will not turn over. You can see it at a glance and it takes a moment to adjust.

3. Fuel tap and primer bulb

Check the fuel tap is open and, on models that have one, press the primer bulb (the little rubber dome) three or four times. If the bulb does not fill, the petrol is not getting through.

4. The spark plug

Take it out and look at it. If it is black and wet, the engine is flooded: let the plug dry, clear the excess fuel out of the cylinder by pulling the starter a couple of times with the plug out, and put it back. If the electrode is worn or has a white crust on it, replace it: it costs a few euros and it is annual maintenance. While you are there, check the plug cap is making good contact.

5. Blocked air filter

A filter full of dust and dry grass chokes the engine: it starts, coughs and dies. Take it out, tap it clean or replace it if it is paper, and wash it with soapy water if it is foam (let it dry completely and add a little oil). In the Empordà, with the summer dust, they block up more than you would think.

6. Oil level

Many Honda and other engines have a sensor that stops the machine starting if the oil is low, to protect the engine. Check the dipstick with the machine on level ground and top up if you need to. And if the mower has been tipped over for cleaning, oil can find its way into the cylinder: it will smoke white for a few minutes and then clear itself.

7. Jammed blade

Compacted dry grass under the deck or a stick wedged in there can lock the blade solid, and the engine with it. With the plug lead off, tip the machine and clean the deck out with a scraper. And if the blade has hit a stone, check the shear key or the clutch has not broken.

8. The carburettor

If you have done all of the above and the engine still will not start, or it only runs while you hold the primer bulb in and dies straight after, the fine passages in the carburettor are blocked with varnish from stale petrol. It can be stripped and ultrasonically cleaned, or replaced: it is the workshop's most frequent April repair, and it usually works out cheaper than a new machine.

And if it is battery-powered?

Battery mowers have none of those problems, but they have their own: a battery run completely flat over winter (always store it at half charge), the safety key not fitted, dirty contacts, or the same jammed blade. If the battery will not take a charge, it needs testing in the workshop: often it is the battery, not the machine.

Avoid it next year

All of this is avoided with proper winter storage: fuel drained or stabilised, fresh oil, clean filter and a checked spark plug before you put it away. And if you would rather not touch it, bring it to the workshop in winter, when we are quieter: we will hand it back ready for the first cut. Give us a call and, if the machine is a big one, we can collect it from your home.