What Fuel Should Be Used on a Four-Stroke Engine?

Clean and fresh regular unleaded gasoline should be used on a four-stroke engine. The gasoline should be a minimum of 87 octane, and up to 10 percent ethanol or 15 percent methyl tertiary butyl ether is acceptable for use.

Consider the following guidelines when using a four-stroke engine:

  • Do not mix oil with the gasoline for a four-stroke engine, as this can damage the engine's components.
  • Do not modify the engine to use alternate fuels, as this can also damage the engine's components.
  • Change fuel brands or providers if engine problems occur.
  • For altitudes above 5,000 feet, perform a high-altitude adjustment. Without the required adjustment, the engine will experience decreased performance, increased emissions and increased fuel consumption. Do not operate the engine with the high-altitude adjustment at altitudes lower than 2,500 feet.
  • Keep the fuel fresh and do not use once it has gone stale, as it can cause acid and gum deposits on carburetor parts or in the fuel system. To keep fuel fresh, either use within 30 days or use a fuel stabilizer drip concentrate cartridge in the fuel. If the fuel stabilizer has been used, simply run the engine for 2 minutes to circulate the fuel and stabilizer, and the engine can then be stored for up to 24 months. If the stabilizer has not been added, the fuel needs to be completely drained from the engine after 30 days.