Turn off the Stihl 310 chainsaw and unplug the spark plug wire from the spark plug. Stand the chainsaw on its back with the chain pointing up.
Find the oiler adjustment screw on the bottom of the chainsaw body. The screw has an "E" stamp and a picture of a chain link on the outside circumference.
Turn the screw with a flat-head screwdriver so that the slot on the screw is pointing to the "E" marking. This is where the oiler is set from the factory.
Rotate the screw clockwise to increase the chain bar oil flow, if you are using a longer chain bar or the wood you are cutting dries out the chain. Turn the screw counterclockwise if you need to decrease the oil flow.
Plug the spark plug wire back onto the spark plug and operate your Stihl chainsaw as normal. Inspect the chain periodically to make sure that it stays lubricated. Adjust the oiler as necessary.