How To Start A Lawn Mower That Has Been Sitting
If your mower has been sitting in the garage through winter or for several weeks, it can feel like a cranky old friend who needs a little coaxing. I’ve rescued more than one neglected mower in my yard — sometimes it takes five minutes, sometimes a bit more work. In this guide I’ll walk you through the practical steps, common problems and quick fixes so you can get your machine humming again without paying a mechanic.
First things first: safety and basic inspection
Before you touch the starter, make sure safety comes first. I always clear the area, wear gloves and eye protection, and disconnect the spark plug if I’m going to work on the engine.
Quick safety checklist
- Work outdoors or in a well-ventilated area.
- Move the mower to level ground and set the parking brake if it has one.
- Disconnect the spark plug wire to avoid accidental starts.
- Remove any debris, grass, or build-up around the engine and muffler.
Common reasons a mower won’t start after sitting
From my experience, these are the usual suspects:
- Stale or separated fuel
- Clogged carburetor or fuel lines
- Dead battery (on electric start models)
- Fouled spark plug
- Old oil or low oil level
“Most of the time, it’s the gas. Old fuel turns gummy and chokes the carburetor. A handful of simple checks usually gets my mower running again.” — A gardener who’s learned the hard way
Step-by-step routine to start a mower that’s been sitting
Follow these steps in order. I recommend taking your time on the fuel checks and carb cleaning — they solve most problems.
Inspect and refresh the fuel
- Smell the fuel: if it smells sour or varnishy, drain it. Stale gas (older than 30 days) is often the cause.
- Drain the fuel tank into a suitable container or siphon it out. Tip: a small hand pump works well.
- Inspect fuel lines for cracks or leaks and replace if brittle.
- Refill with fresh, unleaded gasoline. If your mower sits frequently, add a fuel stabilizer to keep gas fresh.
Check the spark plug
- Remove the spark plug and inspect it. If it’s fouled, black, or rusty, replace it — they’re inexpensive.
- Check the spark: reattach the plug boot, ground the plug against the engine, pull the starter and look for a bright blue spark. No spark? Check ignition coil and wiring.
Examine the carburetor and air filter
- Air filter: a clogged filter starves the engine. Replace if dirty or oily.
- Carburetor: old gas often leaves varnish in the carburetor jets. If the engine cranks but won’t run, the carb may need simply a quick clean or a rebuild kit.
- Try spraying carburetor cleaner into the intake and primer bulb (if present) to dislodge varnish. For heavy buildup, remove the carb and clean the jets or soak the bowl in carb cleaner.
Oil, battery, and other checks
- Check oil level and condition. Change if dirty or if the mower has been idle for 6+ months.
- For electric start mowers, charge the battery fully. If the battery won’t hold a charge, replace it.
- Inspect the fuel filter and replace if clogged.
Starting technique
- Reattach the spark plug wire after you’ve done inspections.
- Set the choke: cold engine = choke on; warm engine = choke off or set to run. Follow the manufacturer’s recommended choke setting if you know it.
- If you have a primer bulb, press it 3–6 times to push fresh fuel into the carburetor.
- If it’s a pull-start, use firm, full pulls. If it’s electric, turn the key or press the start button while holding the brake/clutch as required.
- If it floods, remove the choke, depress the throttle slightly and crank until it clears.
Troubleshooting if it still won’t start
Sometimes one pass through the checklist isn’t enough. Here’s what I do when the mower is stubborn.
Engine cranks but won’t start
- Try a small shot of starting fluid into the air intake. If it fires, it’s a fuel delivery issue—clean the carb.
- Check compression: low compression suggests internal engine problems and may need professional help.
Engine won’t crank at all
- Battery dead: jump-start or charge. Check battery connections for corrosion and clean them.
- Starter solenoid or switch faulty: test or replace components if battery is good.
Runs rough or stalls
- Dirty carb or clogged jets—clean or rebuild.
- Air filter clogged—replace.
- Fuel lines or filter clogged—replace.
Prevent this problem next time
From my own yard, I learned prevention saves time and money. Here’s how I avoid having to babysit my mower every spring.
- Use a fuel stabilizer when storing the mower for more than a month.
- Run the engine for a few minutes after adding stabilizer so it reaches the carburetor.
- Change oil and spark plug yearly.
- Store the mower in a dry, sheltered place and cover it.
- Consider draining fuel at season’s end if you won’t use the mower for months.
Final thoughts and personal experience
I remember one spring when my old Craftsman sat through an unusually wet winter. When I pulled it out it wouldn’t budge. I drained the tank, replaced the spark plug, cleaned the carb bowl and — like magic — it started on the third pull. It saved me a trip to the shop and taught me to keep stabilizer on hand.
Starting a lawn mower that’s been sitting often comes down to fuel and carburetor care. With a few tools, a fresh spark plug and a bit of patience, you can usually bring your mower back to life in an afternoon. If you ever feel stuck, take photos of parts and ask your local small-engine repair shop — they’re usually happy to diagnose over the phone.
If you found this helpful, leave a comment with your mower model and symptoms and I’ll share specific tips I’ve learned from years of mowing and fixing. Happy mowing!
