A Stihl chainsaw uses a two stroke engine. Two-stroke engines require a petrol and oil mixture for operation. A two-stroke engine fires more rapidly than a four-stroke engine, making them more powerful for their size but using the proper oil and petriol mix is necessary to keep the engine lubricated. It is usually necessary to prepare the mixture yourself.
Set up in an open, bare area so that any spillage will not pose a potential risk. Petrol is extremely flammable and does not evaporate quickly.
Pour the correct amount of Stihl two-stroke engine oil into an empty petrol container. The mix ratio for a Stihl chainsaw is 50 parts petrol to 1 part oil. For each 4.5 litres (1 gallon) of petrol, 77 ml (2.6 oz) of oil should be used. The Stihl oil mix comes packaged in 77 ml, 154 ml, 190 ml, 380 ml, 4.5 litres, 22.5 litres and 137.5 litre (2.6 oz, 5.2 oz, 6.4 oz, 12.8 oz, 1 gallon, 5 gallon and 55 gallon) containers. You should be able to purchase the right size containers for easy mixing, in that you can pour a whole container in to match the gasoline ration amount needed. Optionally, you can use a measuring cup to measure out the correct amount of oil mix.
Pour the petrol into the container. It is best only to mix enough fuel for immediate usage. It is not recommended to store the petrol/oil mix for longer than three months.
Secure the cap on the fuel container and shale it thoroughly to mix the oil and petrol.
Occasionally clean the fuel container to ensure that dirt and impurities are kept out of the gas/oil mixture.
Use only air cooled engine oils. Water cooled oils will harm the engine.