Why Your Lawn Mower Won’t Start After Winter
Old fuel, a gummed-up carburetor, a tired spark plug, or a dead battery are the usual reasons a mower won’t start in spring. Here’s what to check first.
A mower that ran fine in October and won’t start in April is one of the most common small-engine problems there is. In most cases nothing dramatic broke over the winter. Something about the fuel, the spark, or the air supply changed while it sat.
Here are the usual causes, roughly in the order worth checking, plus the point where it makes sense to stop and have someone look at it.
Safety first
Before you check anything near the blade or the engine, disconnect the spark plug wire and make sure the engine is cool. On a riding mower, take the key out and set the parking brake. Work outdoors, away from any flame, if you’ll be near fuel.
1. Fuel that sat all winter
Gasoline doesn’t keep well. Most pump gas in Michigan contains ethanol, and over a few months it can absorb moisture and break down. Stale fuel can leave varnish in the carburetor’s small passages, and an engine may crank but not fire, or start and then die.
What to check:
- Does the fuel smell sour or look darker than fresh gas?
- Was fuel stabilizer added before the mower was put away?
If the gas is several months old, it should be drained into an approved container and disposed of properly (many local household hazardous-waste programs take it). Refill with fresh fuel of the type your owner’s manual calls for.
2. A carburetor clogged by old fuel
If fresh fuel doesn’t solve it, the carburetor is the next suspect. The jets in a small-engine carburetor are tiny, and varnish from old fuel can block them. Typical signs are an engine that only runs with the choke on, surges up and down, or won’t start at all.
Carburetor work involves fuel and small parts that are easy to damage or reassemble wrong. This is usually the point where it makes sense to bring it in.
3. The spark plug
A fouled, worn, or loose spark plug can keep an engine from firing. With the wire disconnected, you can remove the plug and look at it. Heavy black carbon, oily residue, or a cracked insulator are signs it needs replacing. Use the plug type listed in your owner’s manual and don’t overtighten it.
4. A dirty air filter
A filter clogged with dust and grass clippings starves the engine of air. Paper filters are generally replaced, not cleaned. Foam filters can often be washed, but check the manual for your model.
5. Battery and safety switches (riding mowers)
Riding mowers have a battery that can drain over a long Michigan winter, especially in a cold garage. They also have safety switches under the seat, on the brake, and on the blade engagement. A seat switch or a blade lever left engaged can stop a mower from cranking even when everything else is fine.
6. Oil level
Some engines have a low-oil sensor that prevents starting. Check the dipstick on level ground. Oil that’s low, very dark, or milky is a separate problem worth addressing before the season starts.
When to call
If you’ve tried fresh fuel, the plug, and the air filter and it still won’t start, or if you see fuel leaking, hear grinding or knocking, or notice smoke, stop there. Call or text Westland Small Engine Repair at (734) 400-0790 with the brand, the model if you have it, and what the mower is doing.
Preventing it next year
The simplest prevention is handling fuel before storage: either add stabilizer and run the engine for a few minutes so it reaches the carburetor, or run the tank dry, following your owner’s manual. See how to store outdoor power equipment during the off-season for the full checklist.
This article is general guidance. Always follow the owner’s manual for your specific machine.