1985-1995 Polaris ATV and Light Utility Hauler Service Manual, Page 274Get this manual
ENGINES Oil Pump 300 Oil Pump Check Valve Testing
The oil pump check valve on the EC28PF engine must be tested by applying to inches of mercury vacuum to the line spigot of the check valveUse aMity VacTM (PN 2870975) or similar vacuum tester