1989 Ski-Doo Repair Manual, Page 228Get this manual
Section 02 ENGINE Sub-section 10 (CARBURETORFUEL PUMP)
Check fuel pump valves operation as follows: Connect length of clean plastic tubing to the inlet nipple and alternately apply pressure and vacuum with the mouthThe inlet valve should release with pressure and hold under vacuumRepeat the same procedure at the outlet nippleThis time the outlet valve should hold with pressure and release under vacuum