Symptoms
- Ran fine last fall, won't start this spring
- Fuel in the tank looks dark, cloudy, or smells sour
- Pull cord feels normal but engine won't catch
- May smell strongly of stale gasoline
Likely causes
- CommonOld gasoline turned to varnishGasoline breaks down within a few months and leaves gummy deposits in the carburetor.
- CommonClogged carburetor jetsVarnish from evaporated fuel blocks the small passages the engine needs to run.
- PossibleCorroded spark plugHumidity during storage can corrode the plug tip over months of sitting.
- PossibleDead battery (riding mowers)Batteries lose charge over winter, especially without a maintainer.
What to do
- Drain any old fuel from the tank into an approved container for proper disposal.
- Refill with fresh gasoline, adding fuel stabilizer if you plan to store it again later this year.
- Remove and inspect the spark plug; clean corrosion or replace it if it's pitted or worn.
- Check the air filter and replace it if it looks dirty from the prior season.
- For riding mowers, charge or jump the battery and confirm it holds a charge.
- Attempt to start; if the engine still won't run cleanly, the carburetor likely needs to be cleaned of varnish.
Tools and parts
- Fuel container
- Spark plug socket
- Battery charger (if riding mower)
Fuel stabilizerSearch: “small engine fuel stabilizer”
Fresh spark plugSearch: “lawn mower spark plug”
When to call a pro
If fresh fuel and a new plug don't get it running, a shop can clean the carburetor of varnish buildup.
Safety
Use caution
Handle and dispose of old gasoline properly; never pour it down a drain or onto the ground.