If you do one thing for your lawn mower all year, winterize it before storing it. The number one cause of "won't start" calls in the spring is a carburetor gumed up by stale fuel that sat in the tank all winter. A proper winterization takes 30 minutes and saves you a $100+ carburetor rebuild.
Why Winterizing Matters
Small engines are not designed to sit idle for months. When fuel sits in the carburetor, the volatile compounds evaporate and leave behind a varnish-like residue that clogs the tiny jets and passages. By spring, the engine either won't start at all or runs rough and surges. Additionally, old oil left in the crankcase can form acids that etch the cylinder walls, and a battery left connected will slowly discharge and sulfate.
Step 1: Stabilize the Fuel or Drain It
You have two options:
Option A — Fuel Stabilizer (Recommended): Add a fuel stabilizer like STA-BIL to a full tank of fresh fuel. Run the engine for 5–10 minutes so the treated fuel flows through the entire carburetor. This prevents varnish from forming during storage.
Option B — Drain Completely: Run the engine until it runs out of fuel. Then drain any remaining fuel from the tank and carburetor bowl. This is more thorough but harder to do completely — a small amount always remains.
I recommend Option A for most homeowners. It's simpler and just as effective.
Step 2: Change the Oil
Old oil contains combustion byproducts and moisture that can corrode engine internals over winter. Change the oil while the engine is warm (after running it with stabilizer) so it flows freely. Use the oil weight specified in your owner's manual — typically SAE 30 for most mowers.
Step 3: Clean the Deck
Tip the mower spark-plug-side up (never carburetor-side up — oil will flood the cylinder). Scrape the grass buildup from under the deck with a putty knife. A clean deck prevents rust and improves cutting performance next season. Spray the clean deck with a light coat of WD-40 or silicone spray to prevent rust.
Step 4: Remove and Inspect the Spark Plug
Remove the spark plug and inspect it. If it's fouled, gapped incorrectly, or has visible wear, replace it. Pour about a tablespoon of clean engine oil into the spark plug hole, then slowly pull the starter cord a few times to distribute the oil across the cylinder walls. This prevents the cylinder from rusting during storage. Reinstall the plug.
Step 5: Disconnect and Charge the Battery
For riding mowers and electric-start push mowers, disconnect the battery's negative terminal. Store the battery in a cool, dry place and put it on a trickle charger or maintenance charger. A battery left in a cold garage all winter will discharge and may not recover.
Step 6: Store in a Dry Location
Store the mower in a dry, covered location. If you must store it outside, use a fitted mower cover — not a tarp, which traps moisture and causes rust.
Spring Start-Up Checklist
When spring arrives:
- Check the oil level
- Reconnect and charge the battery
- Fill with fresh fuel (do not use last year's stabilized fuel if it smells stale)
- Clean or replace the air filter
- Check the spark plug gap
- Start the engine and let it warm up
If the engine won't start after proper winterization, the most likely cause is a dead battery (riding mowers) or stale fuel. If you skipped winterization and the mower won't start, search your specific problem on Lil Engine for a model-specific troubleshooting guide.