Preparing the correct fuel mixture for a two-stroke gasoline engine requires determining the correct ratio of gasoline to oil for the engine in question and then mixing at the correct ratio. Ratios of 32:1, 40:1 and 50:1 are commonly used. The ratio required by a particular engine is specific to that engine and should be listed in its documentation.
Mixing gas and oil for a two-stroke gasoline engine requires attention to safety as well as to the proper fuel mixture ratio for the engine. Using a proper gasoline container that is designed to prevent spills and emissions helps reduce hazards from fire and from inhaling hydrocarbon emissions. It is also wise to avoid storing more than a few days worth of fuel and oil mixture at one time to reduce the risk of fire and to keep the mixtures fresh. In addition, using gasoline with an octane rating of at least 89 and making sure dirt and debris do not enter the mixture during preparation help keep two-stroke engines running optimally.
Though all two-stroke engines require specific fuel and oil ratios, some manufacturers design all their engines to use a specific ratio. For example, all modern Stihl two-stroke engines run on a 50:1 gasoline to oil mixture. Some two-stroke motors may also require a break-in period where more oil is required than normal. In most cases, this break-in mixture is composed of twice as much oil as in the normal mixture.