1971-1973 Arctic Cat Snowmobiles Factory Service Manual, Page 79Get this manual
CARBURETION (NALBRO) Idle Operation
When the engine is idling the throttle valve is partially openDuring the idle process, fuel flows from the idle take off to the idle pocket where it is mixed with air from the secondary idle holesThis rich mixture passes by the idle needle through the idle discharge port
NOTE: The entire carburetor is at atmospheric pressure during idle operation