A Stihl-brand leaf blower runs on a mixed fuel formula that combines gasoline and oil. Since these engines have no oil pump, all their lubrication comes from this gas to oil ratio. This ratio, set by the manufacturer, will keep the engine running at peak efficiency while offering sufficient protection from overheating.
The Oil Type
A Stihl leaf blower can't use just any type of oil; it needs oil designed specifically to mix with gasoline and distribute across the cylinder and crankcase. Other engine oils, such as automotive oil, will not break apart inside the gasoline, so they should never be used. The required oil also needs to be formulated for use in air-cooled engines. Stihl manufactures its own brand of engine oil, which can be used in all of the company's leaf blowers. However, any high-quality oil designed for use in two-cycle air-cooled engines will work fine.
The Gas Type
The two-cycle engine inside a Stihl leaf blower needs to revolve at very high speeds to generate enough power to push the air out through the handle and move the leaves. For this to happen, the gasoline needs to be a higher-grade, high-quality gasoline, as other types will not burn at a high enough temperature to produce adequate power. Stihl recommends using a fuel with a grade of 89 octane or higher. Don't use gasoline blended with additives, such as ethanol, and never use diesel fuel.
The Gas to Oil Ratio
Stihl sets its gas to oil ratios at its factories. These ratios are designed to deliver the best performance under the largest range of operating factors. Stihl sets its ratio for leaf blowers at 50:1, gas to oil. This will allow the fuel to burn up hot enough, while the oil will keep the seals around the piston and cylinder protected from overheating. It's best not to alter this ratio, as improperly balanced fuel can cause permanent damage to the machine.
Oil and Gas Tips
To get the fuel blended properly, mix the oil into a clean fuel container before pouring the gasoline on top. Close the container, and shake the contents for at least one minute. Shake the fuel container before each refueling stop. Don't mix up too much fuel because it will start going bad after 30 days, and will leave behind gummy deposits in the fuel system that will require extensive cleaning and repairs to fix. For this same reason, never store the leaf blower with fuel still inside the tank and carburetor.