Husqvarna chainsaws use an adjustable carburettor to regulate the fuel and air mixtures at different engine speeds. The carburettor screws control the idle, low and high operating speeds for the Husqvarna. Carburettors come preset from the factory, but, after a lengthy break-in period, some will require readjustments. These readjustments are necessary to optimise the engine's performance. However, adjusting the carburettor improperly, or excessively, will cause engine damage and may even ruin it. Let a professional mechanic adjust the high-speed screw.
Unscrew the cylinder cover, which sits atop the engine protecting the cylinder and air filter. Remove the air filter from its mounting seat just above the carburettor. Wash the filter in warm soapy water and rinse under cool water. Let it dry for a minimum of two hours.
Unhook the Husqvarna's cap to the fuel tank. Dump out all old or bad gas that's been in the saw for more than 72 hours. Remix a fresh batch of Husqvarna chainsaw fuel according to your model's fuel specifications. Fill the tank with the freshly mixed gas.
Start the Husqvarna chainsaw and run it at a high idle for a few minutes to warm up. Identify the idle and low-speed adjusting screw holes, on the left side of the engine, near the throttle handle.
Insert the small screwdriver into the hole marked "T" for the idle speed. Rotate the screw clockwise slowly until the clutch engages and the chain starts rotating. Reverse the direction of the screw counterclockwise until the chain stops spinning. Fine-tune the idle speed to the highest speed before the clutch engages and the chain starts spinning.
Insert the small screwdriver into the hole marked "L" for the low speed. Rotate the screw clockwise slowly until the engine starts surging in a higher-pitched whine. Reverse the direction of the screw to counterclockwise and turn the screw until the engine starts producing gurgling or bubbling sounds.
Fine-tune the low speed in between these two points. Listen for the best, smoothest engine sounds. Readjust the idle-speed screw after finishing the low-speed setting, as it will likely have changed slightly.