The idle speed on a McCulloch Mac 130 chain saw regulates the amount of gas flowing into the carburettor when the engine is idling. This speed, through a small screw, can be adjusted to increase or decrease the idle speed. By opening and closing a vent on the carburettor, you can regulate the idle speed. The idle speed needs adjusting if the chain spins while idling, if the chain saw dies when idling and after the low speed is set on the carburettor.
Open the Mac 130's fuel container and empty all remaining fuel into an approved fuel container. Fill the chainsaw with freshly mixed fuel for the Mac 130.
Unscrew the cylinder cover atop the engine with the screwdriver. Take the cover off and lift out the air filter just beside the cylinder. Brush the foam pad and the area around the filter and cylinder fins. Put the air filter and cylinder cover back on.
Start the Mac 130's engine and locate the idle adjusting screw, on the side of the engine, just beside the air filter and carburettor's location. Let the engine reach operating temperatures before adjusting the idle speed.
Insert the small screwdriver into the hole marked "I" for idle. Rotate the screw clockwise slowly until the clutch engages and the chain starts spinning. Rotate the screw counterclockwise slowly until the chain stops spinning. Find the highest idle speed before the clutch engages and the chain starts spinning.
Don't over-adjust the idle speed, which can damage the engine.