1970-1979 Ski-Doo Snowmobiles Service Manual, Page 43Get this manual
CHAPTER TWO
3If state of fuel! air mixture cannot be determined by color of exhaust manifold or spark plug insulator, assume mixture is too lean and increase jet sizeIf operation improves, continue increasing jet size until maximum performance is achievedIf operation gets worse, decrease jet size until best results are obtainedOFF-SEASON STORAGE
5Without changing adjustment of air flow control, place air flow meter on left carburetorIf carburetors are equal, no adjustment is necessary6If adjustment is necessary, loosen cable adjuster locknut on carburetor with lowest float level and turn adjustor until air flow matches other carburetorTighten locknut7Return engine to idle and repeat Steps 3, 4, and 5Adjust throttle stop screws as necessary for balanced idleMikuni Carburetor Main Jet Selection
The main jet controls the fuel metering when the carburetor is operating in the Y2 to full throttle rangeSince temperature and altitude affect the air density, each snowmobile owner will have to perform the following trial and error method of jet selection to obtain peak engine efficiency and performance for his own particular area of operationCAUTION