1971-1973 Arctic Cat Snowmobiles Factory Service Manual, Page 80Get this manual
CARBURETION (VVALBRO) 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 enters past the check valve, through the passage hole, around the power needle, and through the passage holesThe fuel is then discharged into the throttle bore through the three (3) part throttle holesAir is introduced to the increased fuel demand through the air bleed nozzle