Why won't my lawn mower start in spring?
Updated August 2026
A mower that cranks but will not catch after sitting all winter is almost always choking on stale, gummed fuel that varnished the carburetor during five or six months in the tank. Ethanol gas starts breaking down in about a month, so by spring the jets are clogged and the fuel is half dead. Drain it, refill with fresh, and most mowers wake right up; a fouled plug and a dirty filter are the next things to rule out.
Safety first: old gasoline and its vapors are still flammable after a winter in the tank, so drain it outdoors into an approved container, keep it well away from any flame or spark, and store it for proper disposal rather than pouring it out. Disconnect the spark-plug boot before you clean the carburetor or clear the blade area, and when you tip a mower, keep the carburetor side up so oil does not flood the cylinder.
Causes, most likely first
| Cause | How likely | The fix | Typical cost |
|---|---|---|---|
| Stale, varnished fuel from winter storage | Most common | Drain the tank and carburetor bowl, refill with fresh gas, and clean the jets if needed. | $0–80 |
| Fouled spark plug | Common | Replace the plug and gap it to spec; clean a lightly tan tip and reuse it. | $4–10 |
| Dirty or oil-soaked air filter | Common | Swap a clogged paper element or wash and re-oil a foam filter. | $8–15 |
| Old oil or a low level tripping the interlock | Occasional | Change the oil and top to the full mark; some engines block starting on low oil. | $5–20 |
| Cracked primer bulb or stuck choke | Occasional | Replace a hardened primer bulb and free the choke so it can prime and start. | $3–15 |
Check these first
- Drain the stale gas from the tank and, if you can reach it, the carburetor bowl, then refill with fresh fuel.
- Pull the spark plug. A wet, black, or fouled tip will not fire; clean or replace it and gap it to spec.
- Check the air filter and swap a dirty paper element; a clean filter is often the difference between catching and not.
- Look at the primer bulb: a cracked or hardened bulb will not push fuel, so prime three to five times or replace it.
- Verify the oil level, because some mowers use a low-oil interlock that blocks starting.
Prevent it next time
A spring no-start is the bill for skipping fall storage prep. Stabilized fuel or a dry tank before winter keeps the carburetor clean, which is the whole point of a winterizing routine. Pair that with the yearly basics: a new spark plug, an oil change, and a sharpened blade, and the mower fires on the first or second pull in April.
When to call a pro
Hand it to a pro when a drained tank, fresh gas, a new plug, and a clean filter still will not fire, which points past fuel to ignition or compression. Expect $50–100 for a shop diagnostic and $80–200 for a full tune-up with carburetor service. If the engine has low compression from a worn ring or a bent valve, repair costs climb toward the price of a new mower ($250–600), and replacement becomes the smarter call.
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Stop chasing symptoms, free for 30 daysFrequently asked questions
Is it worth reviving a mower that won't start, or should I buy new?
Almost always worth reviving. The usual spring fix, fresh fuel, a $4–10 spark plug, and an $8–15 air filter, totals under $30 and an hour of work, against $250–600 for a new push mower. Revive it unless the engine has a deeper fault: low compression, a cracked block, or a seized crank. If you have done the fuel, plug, and filter and it still will not catch, a $50–100 shop diagnosis tells you whether you are throwing good money after a tired engine.
How do I get the old gas out safely?
Work outdoors, well away from any flame, water heater, or spark. Siphon or pump the tank into an approved gas can, then, if you can reach it, loosen the carburetor bowl's drain screw to empty the varnished fuel sitting there, which is what actually clogs things. Do not pour old gasoline down a drain or onto the yard; most hazardous-waste sites and many auto stores take it free. Refill with fresh gas and, if the mower will sit again, add stabilizer.
Do I need a new spark plug every spring?
Not always, but it is cheap insurance. A spark plug lasts roughly 100 hours or a season or two of typical mowing, and a fouled or worn plug is a leading spring no-start once fuel is ruled out. Pull it: a light tan tip can be cleaned and regapped, while a black, oily, or eroded tip should be replaced for $4–10. Our guide on how often to change a mower spark plug covers the gap spec and the hour interval.
Will starting fluid hurt my mower?
A quick spray to diagnose is fine, but do not lean on it. Starting fluid is ether, which ignites hard and can wash the oil off the cylinder wall or, on some engines, cause damage if overused. If the mower only runs while you spray fluid into the intake, that confirms a fuel-delivery problem, a gummed carburetor or an empty bowl, not an ignition fault. Fix the fuel side rather than dosing it every start.