1971-1973 Arctic Cat Snowmobiles Factory Service Manual, Page 94Get this manual
CARBURETION (TILLOTSON) Part Throttle Operation
Fuel is introduced into and passes through the carburetor in the same manner as during engine idle operationAs the throttle is opened and the engine speed increases, more fuel is demanded from the carburetorThe additional fuel necessary for part throttle operation is supplied to the engine by valving in the secondary idle discharge port located immediately behind the throttle shutterAs the throttle shutter continues to open and the engine speed increases, the velocity of air passing through the venturi creates low pressure area at the venturi throat and diminishes the suction on the engine side of the throttle shutterWhen the pressure at the venturi throat is lower than the pressure within the main diaphragm fuel chamber, the fuel is drawn up through the main adjustment screw orifice, out through the main fuel discharge port, and into the air stream entering the engine intake