A Husqvarna chainsaw should idle around 2,800rpm. If the engine idles higher than this, the clutch will stay engaged and the chain will continue to turn. Besides forcing the carburettor and engine to work harder, this idling problem can be dangerous for a sawyer, as the chain continues to spin without throttling the saw.
How Idling Works
The carburettor on a Husqvarna chainsaw pulls fuel in from the tank, measures the required amount of fuel for the given engine speed and mixes it with air before finally sending it off to the cylinder. The throttle lever on the outside of the carburettor opens and closes the jets, allowing more or less fuel into the carburettor when the throttle is triggered. When the engine idles, the throttle lever should stay closed, and a small amount of fuel, just enough to keep the engine running, will run through the carburettor. If the engine idles poorly, the carburettor is receiving too much fuel after the trigger is released.
Before Adjusting Idle
To solve this idling problem on a Husqvarna chainsaw, you'll need to adjust the idle speed on the carburettor. However, before the idle speed can be adjusted, you will need to make sure the air and fuel systems are cleaned. Pull out the air filter from the box, and brush off the area around the box and the carburettor. Shake off any loose debris, slapping the pad against your palm. Dump out any gas older than one week, and refill the tank with freshly mixed fuel at a 50:1 gas to oil ratio. Fill the tank at least three-quarters full.
Adjust Idle Speed
Locate the idle speed screw, which on most Husqvarna chainsaws will be located on the starter side of the engine and is accessed through a small hole. Use a small screwdriver to turn the screw slowly counterclockwise until the engine speed slows and the chain stops spinning. Move the idle speed screw back in slowly clockwise, looking for the highest possible engine speed before the clutch engages and the chain starts spinning. Adjust the screw slowly, making sure not to turn it in or out too quickly.
Adjust Low Speed
Once the idle speed has been reset, the low speed on the carburettor will also need adjusting. The low speed screw sits just above the idle speed screw hole. Turn in the low speed screw slowly clockwise until the engine produces a surging or whining noise. Slowly turn the screw back counterclockwise until the engine makes a deeper, bubbling sound. Adjust the screw in between these two points, so the engine produces a clean, smooth sound. Press in the throttle and check the acceleration. If the acceleration is sluggish, move the screw clockwise one-eighth of a turn until it picks up. After adjusting the low speed screw, go back and readjust the idle speed, as the setting will have changed.