Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 82Get this manual
FUEL PUMP Remove screws and plate from pump cover to inspect check valve
- StopCheck Valve (Clear Plastic)Check ValvePlateScrew (2)
4Inspect check valve, gasket, and diaphragmReplace if damaged5Replace plunger if tip is warn or groovedaCheck ValveDiaphragmGasketPlunger Tip