Mercury Optimax Diagnostic Guide., Page 6Get this manual
OPTIMAX DIAGNOSTIC GUIDE
Procedure 3
PULSE FUEL PUMP
The fuel pump is crankcase-pressure-operated, diaphragm-type pumpCrankcase pulsating pressure (created by the up-and-down movement of the piston) is transferred to the fuel pump by way of passage (hole) between the crankcase and the fuel pumpIf the pulse fuel pump diaphragm(s) are leaking, spark plug fouling will occur on cylinders andor that supply the pulse pressure to operate the pumpRemove the outside pulse hose from the pump and remove the pump from the engineSqueeze the primer bulb on the fuel supply hose and look for fuel leaking from the pumpBoth should be dry with no fuel presentIf leaking is evident, replace the diaphragms59488 59487