A properly running saw is essential to safe and productive tree felling. Everyone who operates a chain saw should understand how to adjust the carburetor. Even if you choose not to adjust the carburetor yourself, you should understand when a carburetor is out of adjustment and needs to be tuned by someone with the proper skills.
The following are the steps for adjusting the carburetor:
1. Check and clean the air filter on a routine basis.
2. Balance the high and low speed screws - Start and warm the saw to operating temperature. The high and low speed screws are turned completely in (clockwise). Each screw should then be backed off (counter-clockwise) to the left one full turn (or some other amont according to the instructions in you owner's manual.)
The high speed screw is then turned clockwise to reduce fuel (clockwise reduces fuel). As the fuel mixture is leaned out, the saw will run faster until it sounds as if it is screaming. At this point, turn the high speed screw to the left to allow more fuel until a "flutter" is heard. This is the proper RPM for your saw.
This can be confirmed with a tachometer, but a tachometer alone cannot ensure that you have the right fuel mixture. It is possible that air leaks may prevent you from obtaining the proper fuel and air mixture and you may need to reduce the RPM to hear the "flutter". Therefore, the "flutter" is more important than the tachometer reading. Chain saw operators must understand that the fuel mixture accomplishes two additional functions--cooling of the motor and lubricating the engine. If the saw runs too lean, neither of these functions are accomplished effectively and the saw will be ruined.
3. Throttle - Ensure that the saw chain is not moving when the saw is on idle. If the chain is moving, turn the throttle screw counter-clockwise to slow the chain to a stop.
4. Roll-over Test - With the chain brake engaged, let the saw idle for 10-20 seconds and then turn the saw to different positions. If the saw stalls, it is getting too much fuel, which is puddling below the cylinder. Turn the low speed screw clockwise (reducing the fuel) a little bit and repeat the test.
5. Accelerate - Disengage the chain brake. If there is hesitation in acceleration, the saw motor is not getting enough fuel. Turn the low speed screw counter-clockwise for more fuel and repeat the roll-over test.