Small-Engine Fuel: Stabilizer, Ethanol, and Why Carburetors Gum Up

Ask any small-engine mechanic what they fix most and they'll tell you: carburetors gummed up with old gas. Mowers, trimmers, snowblowers, chainsaws and generators all run on small carburetors with tiny passages, and stale fuel clogs them. Understanding a little about fuel saves you a lot of repair bills.

Why gas goes bad

Gasoline is a blend of compounds, and the lighter ones evaporate over time. What's left breaks down, oxidizes and forms gums and varnish. In a small engine sitting all winter, that varnish coats the carburetor and clogs the jets.

Many sources say untreated gas starts to lose quality in about a month, and can cause trouble after a few months of sitting. Hot garages make it worse.

What ethanol does

Most gas at the pump in the U.S. contains up to 10 percent ethanol (E10).

• Ethanol attracts water. Over time, ethanol fuel can absorb moisture from the air.
• Phase separation: if it takes on enough water, the ethanol and water separate from the gas and sink to the bottom of the tank. That layer can damage engines and won't burn properly.
• Rubber and plastic parts: ethanol can be hard on older fuel lines, seals and carburetor parts not designed for it.

Never use E15 or higher in small engines unless the manufacturer specifically allows it. Many small-engine manufacturers warn against it.

Fuel stabilizer

Stabilizer slows the breakdown of gasoline.

• Add it to fresh gas, not old gas. It can't fix fuel that's already gone bad.
• Mix it in the can when you buy gas, so every tank you fill is treated.
• Run the engine for a few minutes after adding it, so treated fuel fills the carburetor.

Stabilizer extends fuel life, but it isn't forever. Many products claim a year or more; follow the label.

Ethanol-free gas

Sometimes sold as "recreational fuel" or at marinas, ethanol-free gas stores better and is easier on small engines. If it's available near you, it's worth it for equipment that sits a lot. Pre-mixed canned fuels for small engines are another option; they're expensive but store for a long time.

Storing gas

• Use approved fuel containers, sealed tight.
• Store in a cool, dry place, away from living areas and anything with a pilot light or spark.
• Buy only what you'll use in a month or two during the season.
• Label cans with the date and whether stabilizer is added.
• Check local rules on how much fuel you can store at home.

End of season: two ways to store an engine

1. Stabilize and run: fill with stabilized fuel and run it a few minutes.
2. Run dry: run the engine until it stops, so there's no fuel to go bad.

Check your manual for the manufacturer's recommendation.

Generators: extra important

A standby or portable generator has to start the first time, in an outage. Treat its fuel, run it monthly for a few minutes under some load, and keep fresh fuel on hand. Our friends at The Midwest Prepper cover generator safety and sizing a generator.

Signs of bad fuel

• Hard starting or no start.
• Surging, rough running.
• Gas that looks darker or smells sour.

Fresh, treated fuel is the cheapest maintenance you can do for every engine in your garage.

Photo by MatteoBaronti on Pixabay.

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