Chainsaws are extremely rugged machines that are invaluable if you have to trim or down trees on a regular basis. The carburetor on a two-cycle engine that typically comes factory adjusted. However, most chainsaws have two to three fuel mix screws that can be adjusted if the chainsaw runs rough. This is especially useful in high-altitude climates, where altitudes can effect the chainsaw carburetor jets, primarily the high speed jet.
Things You'll Need
Remove the chainsaw's casing with an Allen wrench to access the carburetor adjustment screws. There are typically three adjustment screws, including the idle speed screw, the low speed adjustment screw and the high speed adjustment screw. The idle screw is usually on the top of the engine rear, while the low is on the bottom left and the high is on the bottom right.
Remove the chainsaw's air filter and either clean it or replace it if it is extremely dirty.
Turn all three adjustment screws fully to the right, or until they stop, using a screwdriver. Do not force the screws once they come to rest because it can damage their seats. Turn each screw one full turn to the left.
Check the chainsaw's fuel level, add fuel if needed and then start the chainsaw and allow it to run for about five minutes.
Set the idle speed screw with a screwdriver. Ideally, idle speed should run evenly without the clutch engaging. If the chainsaw blade moves on its own without the throttle being pulled, turn the idle screw to the left in small increments until it stops.
Flip the throttle control to the low speed and adjust the low speed screw by turning the screw to the left until it begins to surge and sound like it is going to die. Adjust the screw in 1/8 turns from this position until the motor runs freely.
Move the saw's throttle level to high and then adjust the high speed screw by turning it in 1/8-turn increments to the right if the engine begins to sputter out. If the engine sounds like it is running too fast, turn the screw in 1/8-turn increments to the left until the engine runs smoothly. Altitude tends to affect a chainsaw carburetor's high speed jet the most, so do not be surprised if the adjustment ends up lower than if you adjusted it at a lower altitude.