Why won't my lawn mower start?
Most mowers that will not start are missing one of three things: fresh fuel, clean air or a good spark. Stale gasoline is the usual cause after a few weeks of sitting, then a clogged air filter, then a fouled spark plug. Your symptom narrows it down: a dead pull cord, a cough with no run, and a start-then-stall each point somewhere different.
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By Kasra Taheri, Founder, LoclisPublished
Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.
Step by step
Read when to stop and call a pro, further down this page, before you start.
Step 1: Disconnect the spark plug wire
Pull the wire off the spark plug before you troubleshoot, so the blade cannot turn if the engine fires.[1]
Step 2: Match the symptom
Note what it does: no sound at all, a cough that will not catch, or a start that dies after a few seconds.
Step 3: Check the simple things
Confirm there is fuel and oil, the safety bar or handle is held as the manual describes, and nothing is jamming the pull cord.
Step 4: Judge the fuel
If the gasoline has been in the tank for a month or more, drain it into an approved container and refill with fresh fuel.[4]
Step 5: Look at the air filter
Take the filter out; if it is packed with dust and debris, replace it with the part the manual lists.[3]
Step 6: Inspect the spark plug
Remove the plug and check that the contacts are clean and free of scoring; replace a dirty or worn plug with the type and gap the manual gives.[3]
Step 7: Reconnect and try once more
Refit the plug and wire, put the mower on level ground and start it with the blade disengaged.[1]
Step 8: Hand it over if it still fails
If fresh fuel, a clean filter and a good plug do not get it running, take it to a small engine shop.
Three things an engine needs
A mower engine needs fuel, air and spark, and a mower that will not start is nearly always short of one of them. Which one depends on how it fails, so start by watching what it does. Before anything else, pull the spark plug wire off the plug. Virginia Cooperative Extension's rule is plain: "Disconnect the spark or electric plug before troubleshooting or repairing the mower."[1]
What the symptom tells you
It turns over but coughs and will not run. This is usually fuel. Briggs & Stratton says gasoline deteriorates after 30 days and can negatively affect engine and starting performance.[4] A mower that sat since the last mow of the season is the classic case.
It starts, runs rough and dies. Think fuel delivery or air: stale gas, a clogged air filter, or a carburetor with varnish in it. A fresh tank and a clean filter settle the first two.
It makes no effort at all. Check the plain things first. Is there fuel and oil? Is the safety bar held down? The rule is "Never disengage any safety switches or devices."[1] A bypassed switch is a hazard and rarely the real fault. A loose or detached spark plug wire is also common.
The cord will not pull. Do not force it. Look for something wedged under the deck, and see the stop signs below.
Old fuel
Fuel is the most likely culprit, especially in spring. Penn State Extension says engines that are rarely or seasonally used, such as lawnmowers or chainsaws, are especially prone to difficulties with ethanol-blended fuel.[2] Penn State Extension explains that ethanol can pick up contaminants that gasoline does not and deposit them inside the engine, which can foul filters or injectors.[2] It adds that on old machinery, ethanol can make seals and hoses deteriorate, shrink or swell, resulting in leaks.[2]
If the fuel is more than a month old, drain it into an approved container and refill with fresh gasoline. Never refuel the mower when its engine is hot or running.[1] Wipe up any spill before you try a start.
The air filter
Air filters keep the engine clean, but they only work if you change them. Illinois Extension notes that an air filter fills with dust and debris over time,[3] and a packed filter starves the engine of air. Pull it out and look. A paper element that is grey and clogged should be replaced with the part your manual lists, and for a foam or reusable filter follow the cleaning steps in the manual.
The spark plug
Remove the plug with a spark plug socket and look at it. Illinois Extension says to check that the contacts are clean and free of scoring, and that plugs are typically changed every two years.[3] A wet, black or crusted plug is a good reason to fit a new one of the type and gap your manual gives. Take care not to cross-thread the new plug,[3] and thread it in by hand first.
Oil level
Briggs & Stratton's advice: "Check the oil level regularly - ideally every time you mow."[4] Check it with the mower level and the engine cold, and top up with the oil your manual specifies.
Try it again
Refit the plug and wire, put the mower on level ground, and start it with the blade disengaged. Virginia Cooperative Extension says to disengage the blade before starting the engine.[1] Keep your feet clear of the deck.
Stop and call a pro if
- It still will not start with fresh fuel, a clean filter and a good plug. The carburetor, ignition coil or a safety switch may need testing, and a shop has the tools to do it quickly.
- You smell fuel or see it leaking. A leaking tank, line or carburetor bowl is a fire risk. Fix the leak before any more starting attempts.
- The cord is locked or the engine feels seized. Forcing it can do more damage.
- The blade is loose, bent or has hit something. Have a shop inspect it with the spark plug wire still off.
- You cannot safely tip or hold the mower to reach the parts.
Getting help in Virginia
For the step-by-step version, read how to fix a lawn mower that won't start. If it needs a shop, what a small engine shop charges to fix a lawn mower explains what drives the bill. You can also browse small engine repair answers or find local mower repair pros.
When you are ready, describe the mower and local small engine shops can quote it.
Common questions
- Why does my mower start and then die?
- Usually the fuel is not reaching the engine steadily: stale gasoline, a clogged air filter or a dirty carburetor. Try fresh fuel and a clean filter first. Briggs & Stratton says gasoline deteriorates after 30 days and can negatively affect engine and starting performance. If it still stalls, a shop can clean the carburetor.
- Why won't my mower start after sitting all winter?
- Old fuel is the most common reason. Penn State Extension says engines that are rarely or seasonally used, such as lawnmowers or chainsaws, are especially prone to difficulties with ethanol-blended gasoline. Drain the tank into an approved container and refill with fresh gasoline.
- Why does the engine turn over but not catch?
- That points at fuel or spark rather than a seized engine. Stale gas, a fouled spark plug or a choked air filter are the likeliest causes, and all three are cheap to check. Disconnect the spark plug wire before you do.
- Why does the pull cord feel stuck or will not pull?
- Do not force it. A cord that will not move can mean a jammed blade, a clogged deck or a seized engine. Disconnect the spark plug wire, check that nothing is wedged under the deck, and take it to a shop if it stays locked.
- Is it safe to troubleshoot a mower myself?
- Yes, for the basics, if you disconnect the spark plug wire first. Virginia Cooperative Extension says to disconnect the spark or electric plug before troubleshooting or repairing the mower, and never to disengage safety switches or devices.
Sources
- [1] Lawn Care: Rotary Mower Safety (BSE-42P), Virginia Cooperative Extension, Virginia Tech. Checked October 27, 2026.
- [2] Fuel Ethanol: Hero or Villain?, Penn State Extension. Checked October 27, 2026.
- [3] Mower Maintenance, University of Illinois Extension. Checked October 27, 2026.
- [4] How to Perform Lawn Mower Maintenance, Briggs & Stratton. Checked October 27, 2026.
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