What Fuel Should Be Used in a Ride-On Mower?

More May Not Be Better

• The configuration of an engine combustion chamber dictates the octane needed. High compression engines, like those in sports cars, require high octane fuels. Using a high octane fuel in an engine designed for less will have no beneficial effect, and may contribute to engine performance problems. The unburned portion of the high octane fuel can form carbon deposits on the top of the piston. The deposits can raise the compression slightly, creating a cause-and-effect cycle.

Vicious Cycle

• As carbon deposits raise the compression, higher octane fuel is required for combustion. The cycle continues and waste matter builds, creating engine knock, or "pinging." The only way to restore proper function to an engine that has been given a "treat" of high octane fuel is to remove the cylinder head and scrape the carbon away. Fuel additives meant to boost power or clean fuel systems may also create this symptom, if inappropriate in dosage or design.

Lead and Alcohol

• No gasoline containing lead has been available for purchase in this country for decades. Antique mowers may require fuel treatments that mimic the properties of lead, or engine modifications to accommodate modern fuel. Mower engines built in recent times are equipped to run well on unleaded gasoline. Mowers can also tolerate ethanol blends in concentrations of 10 percent or less. The regular grade of ethanol blended gasoline for sale at your neighborhood filling station is sufficient, most of the time.

A Long Winter Nap

• Some ride-on mowers are used year round; mulching or bagging leaves in the fall and plowing snow in the winter. However, if your mower is going into hibernation for the off season, special stabilizers should be added to the gasoline. Untreated gasoline in storage for a month or longer can become stale enough to prevent engine starts. Extended storage without proper treatment can lead to the formation of gums and varnishes that obstruct fuel flow.