Symptoms
- Fuel has a sour or varnish-like smell
- Gas looks darker or cloudier than fresh fuel
- Engine hard to start or runs rough
- Mower sat for weeks or months with fuel in the tank
Likely causes
- CommonGasoline aged past its useful shelf lifeEthanol-blended gas typically starts degrading within 30 days without a stabilizer.
- PossibleMoisture absorbed into the fuelEthanol gas can absorb water from humid air over time, especially in a partially full tank.
- CommonNo fuel stabilizer used before storageStabilizer slows the breakdown process significantly if added before long storage periods.
What to do
- Drain the old fuel into an approved container for proper disposal, never down a drain or onto the ground.
- Inspect the fuel tank for rust or sediment and clean it out if visible debris is present.
- Refill with fresh gasoline of the correct octane rating listed in the manual.
- Add fuel stabilizer to any fuel you plan to store for more than a few weeks going forward.
- Run the mower briefly to circulate fresh fuel through the carburetor.
- If the engine still runs poorly after a fresh fuel fill, the carburetor may have already gummed up and need cleaning.
Tools and parts
- Fuel container
- Funnel
Fuel stabilizerSearch: “small engine fuel stabilizer”
When to call a pro
If fresh fuel doesn't restore normal running, a small engine shop can clean varnish deposits from the carburetor.
Safety
Use caution
Dispose of old gasoline at an approved hazardous waste or recycling facility; never pour it out or store it in an unmarked container.