1972 Ski-Doo Shop Manual, Page 170Get this manual
2-07-02 IDLING OPERATION The throttle shutter is in partially open position when the engine 'is idlingEngine suction is transmitted through pri.m8ry idle fuel discharge port to the fuel chamber side of metering diaphragm via the idle fuel supply channelAgain the metering diaphragm is forced upward by atmospheric pressure, depressing the inlet control lever and permitting fuel under pressure to force the inlet needle off its seat and enmr the metering chamberThe fuel is then drawn up through the idle fuel adjustment orifice and delivered to the engine through the primary idle disdlarge portThe entire carburetor bore from the air inlet to the back of the throttle shutter is at atmospheric pressure during idle operationThe ball check valve in the main fuel port is closed to prevent air from entering the metering chamberIn all phases of operation, the amount of fuel entering the metering chamber is equal to the amount of fuel being used by the engineCARBURETOR INTERMEDIATE OPERATION Fuel is delivered into and through the carburetor in the same manner as when the engine is idlingAs the throttle opens and engine speed increases, more fuel is demanded from the carburetor and supplied to the engine by the secondary idle discharge port located immediately behind the throttle shutterAs the throttle shutter con tinues to open and the engine speed increases, the velocity of the air through the venturi creates low pressure area at the venturi throat and diminishes the suction on engine side of the throttle shutterWhen the pressure at the venturi throat is" lower than the pressure existing within the metering diaphragm fuel chamber, the fuel is drawn up through the high speed mixture screw orifice and out through the main fuel discharge port4 "'-