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Lawn Mower Won't Start After Winter: A Manual-Based Checklist

Updated 2026-10-29 · Written and checked by the Manual Matters team against the manufacturer documents listed under Sources.

Short answer: the most common reason a mower will not start after sitting all winter is stale gasoline left in the tank and carburetor. Briggs & Stratton's troubleshooting guide says to drain old gas and refill with fresh fuel first, then check the spark plug, the air filter and the fuel filter. Honda notes that stabilizer will not revive fuel that has already gone stale, so draining is the fix, not adding more stabilizer.

Seven-step checklist for a lawn mower that won't start after winter, from fuel to oil level
Seven-step checklist for a lawn mower that won't start after winter, from fuel to oil level

Before you start

Work outdoors, on level ground, with the engine cold. Disconnect the spark plug wire before touching the blade or underside.

The checklist, in order

  1. Fuel. If the gas is from last season, drain it into an approved container and refill with fresh unleaded gas (Honda specifies no more than 10% ethanol). Briggs says fuel can begin to degrade in as little as 30 days.
  2. Fuel valve and choke. On engines with a fuel valve (many Honda engines), make sure it is ON. Use the choke or primer as your manual describes for a cold start.
  3. Spark plug. Remove and inspect it. Replace it if fouled, cracked or worn, and set the gap your manual specifies (see the Briggs spark plug gap chart). Reconnect the wire firmly.
  4. Air filter. A clogged filter starves the engine. Clean or replace it per the Briggs maintenance schedule or your Honda manual.
  5. Carburetor. Briggs suggests gently tapping the carburetor, which can help after storage.
  6. Fuel filter. If the engine still starves, Briggs lists the fuel filter as the next item; replace it if clogged.
  7. Oil level. Check that oil is between the marks. Overfilled oil can cause smoking and power loss.

If the cord is hard to pull

Briggs lists two common causes: the flywheel brake (blade control) bar is not being held against the handle, or grass clippings are jamming the blade. With the spark plug wire disconnected, clear the deck.

If it starts but smokes or loses power

Briggs links this to overfilled oil, or oil that ran into the muffler after the mower was tipped the wrong way. Correct the oil level, let it run outdoors, and the smoke should clear. Honda's manual says to tip its engines muffler side down only (Honda GCV guide).

Prevent it next year

Choose a storage method from Run it dry or stabilize it? and follow it in the fall.

FAQ

Can I just add fuel stabilizer to old gas?

No. Honda says stabilizer will not restore fuel that has already gone stale. Drain and refill.

What should I do with old gasoline?

Honda's fuel page says the EPA suggests putting small amounts of leftover fuel into a car's tank, where it will be diluted. Otherwise, take it to a household hazardous waste site.

Should I replace the spark plug every spring?

Briggs lists it as an annual job; Honda's GCV manual says every 2 years or 200 hours, with a yearly check.

When should I call a dealer?

If fresh fuel, a new plug and a clean filter do not get it running, the carburetor may need cleaning or rebuilding. That is a dealer job unless you are comfortable with fuel-system work.

Sources