The carburetor on a Stihl chainsaw channels a mixture of two-cycle oil and gasoline into the engine. That mixture, plus dirt or debris that makes it way past the air filter, can cause a gummy sticky mess that will affect the proper function of a carburetor. In time it can cause engine damage. There is a relatively simple and economical way to clean out a carburetor on any Stihl chainsaw.
Remove the bar and chain from your chainsaw with the supplied chainsaw wrench.
Remove the air filter cover with your screwdriver, and pull out the air filter element.
Start your chainsaw.
Hold your chainsaw in one hand with the throttle at about two-thirds.
Spray a one-second blast of carburetor cleaner into the vacant space where the air filter was. The carburetor cleaner will get sucked through all of the carburetor jets and past needle valves, dissolving all the gunk.
Spray another one-second blast for good measure, let the motor run for a bit to burn up any cleaning spray, then shut the motor down and reassemble.