1985 OMC 65, 100 and 155 HP Models Commercial Service Manual, PN 507450-D, Page 103Get this manual
The vacuum reading must be no more than 140 mm (5-12 inches) of mercury for 65 and 100 models, or 178 mm (7 inches) of mercury for 155 modelsIf vacuum reading exceeds maximum tolerance, the fue system warning switch (if equipped) will activate the warning horn with steady soundCheck for proper operation of this circuit as described in this section This test only checks the boat's fuel system for restrictions and does not determine whether you have good fuel pumpThe fuel pump is tested by the pressure test as explained under Fuel Pump Pressure Test Corrections to boat's fuel system must be made to bring the reading on the suction tester within the acceptable range for proper engine performanceSuspected fittings, valves, etc, may be temporarily bypassed with length of hoseIf deletion of an item corrects the problem, then suitable replacement must be installed 1201 '