10-minute spring mower service — UK checklist for under £15
Your mower has been in the shed since October. Half the petrol mowers on Marketplace this week aren't being sold for cash — they're being sold because someone tried to start a neglected machine and gave up. Here's the ten-minute service that prevents you joining them.
What you need
About fifteen quid: fresh E5 petrol (£3 for a 5L can), engine oil (£8 for SAE 30), a new spark plug if yours is over three years old (£4). Plus a spark-plug socket (16mm or 21mm depending on engine) and a screwdriver.
About ten minutes if everything's straightforward. Half an hour if the carb needs cleaning.
1. Drain the old fuel — 2 minutes
This is the single most important step. Modern E5 and E10 petrol degrades in 4-6 months. Last October's fuel is now half varnish.
Tip the mower on its side, drain the tank into a metal container (never plastic — petrol vapour). For Mountfield and Stiga mowers there's a brass screw on the underside of the carb that releases the float bowl too — undo it and let the carb drain.
Refill with fresh E5. E10 works but degrades faster — pay the extra 5p/litre for E5 if you can.
2. Change the oil — 3 minutes
If you didn't change it last autumn, do it now. Tip the mower on its side (filler-cap up), drain the old oil into a tray, refill with fresh SAE 30 or 10W-30 to the dipstick mark.
Honda mowers use Honda 10W-30 SJ specifically — slightly different additive package. Worth the extra £4.
Briggs and Stiga engines are happy with any SAE 30 from Halfords or any motor factor. Don't overfill — too much oil smokes worse than too little.
3. Spark plug — 2 minutes
Pull the plug. A healthy plug is light tan in colour. Black and oily = mixture too rich, replace. White and bone-dry = mixture too lean, replace. Tan and dry = leave it.
Replacement plugs are NGK BPR4ES or BPR5ES depending on engine — £3-£4 at any motor factor or Halfords. Gap to 0.7mm with a feeler gauge or just eyeball it (the new ones come pre-gapped close enough).
4. Air filter — 2 minutes
Pop the air filter cover (one or two screws). Foam filters wash out under warm soapy water, squeeze dry, re-oil with a few drops of motor oil. Paper filters get replaced — never washed.
A grey or black filter is choked. A wet filter is over-oiled. Aim for a uniform yellowy-orange tinge after re-oiling foam.
5. Sharpen the blade — 1 minute
Tilt the mower (spark plug disconnected and pointing up to avoid oil running into the cylinder). Run a flat file along the cutting edge at the original 30° angle. Five passes per side is usually enough for a season's edge.
A sharp blade pays for itself within a week. A blunt blade tears grass — visible as brown tips two days after cutting — and uses 15-20% more fuel.
Now start it
Three primer squeezes (or auto-choke for ReadyStart engines). Pull the cord. A serviced mower fires on the first or second pull when cold.
If it still won't start, the carb has varnished from the stale fuel — see our [Mountfield SP46 won't start guide](/blog/mountfield-sp46-wont-start) for the carb-cleaning steps. Twenty minutes and a £6 can of carb cleaner spray fixes 95% of cases.
Cordless mower? Different rules.
No fuel, no carb, no plug, no oil — but the battery and the blade still want attention. Charge the battery to 100%, then run the mower for two minutes to wake the cells. If runtime is noticeably shorter than last September, the battery is on its way out (typical 3-5 years to 80% capacity on EGO/Stihl/Greenworks).
Sharpen the blade as above — same logic, even more important on cordless because a blunt blade kills runtime fast.
Robotic mower? Power on the dock, check the boundary-loop LED is steady green, replace the cutting blades (£6-£8 a set) and let it self-test. See our [Husqvarna Automower troubleshooting guide](/blog/husqvarna-automower-305-troubleshooting) if anything's amber.
Set the mower height
First cut of the year = highest setting your mower offers (usually 65-75mm). Cutting too short on the first pass shocks the grass and invites moss and weeds.
Drop the height by 5-10mm per cut over the next three weeks until you reach your normal summer setting (typically 35-40mm for a domestic lawn, 25mm if you want a closer ornamental finish).
Never remove more than a third of the grass blade in one cut. That's the single most important rule of mowing — break it and the lawn yellows for a week.
FAQs
What if I forgot to drain or stabilise the fuel last autumn?
About 80% of UK mowers stored with old E5 petrol still start fine after a fresh-fuel swap. The other 20% need a carburettor clean — easy DIY for £6 or £40 at a dealer. Either way, drain first before doing anything else.
Should I service my mower at a dealer instead?
A full Mountfield/Stiga dealer service costs £80-£120 and gets you everything above plus a deck clean, drive-cable check and a 12-month receipt. Worth it once when you buy a used mower; DIY annually after that.
How often does the blade actually need sharpening?
Once a year for domestic use. Twice a year if you cut more than 1,000m² weekly. The £18-£35 you'd pay a sharpener pays for itself in fuel saved and lawn quality. Or learn to file your own — five minutes a season is all it takes.
What about ride-on mowers?
Same checklist plus battery (12V SLA, £45 if dead), tyre pressures (8-10 PSI typical), transaxle fluid level if hydrostatic, and grease all the deck spindles. Most ride-ons hide the dipstick under a fuel-tank cowling — pull the seat to find it. Budget 30 minutes total.
Is it worth doing this if I'm planning to buy a new mower anyway?
Yes, because the wake-up service is also a sale-prep service. A serviced mower with a fresh plug, clean filter and oil change adds £30-£50 to the asking price on Marketplace and sells inside a week instead of three.
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