1985 OMC 65, 100 and 155 HP Models Commercial Service Manual, PN 507450-D, Page 118Get this manual
Fuel System Warning Circuit The fuel system warning consists of vacuum switch mounted to the powerhead with ground connection and wire connected to the warning horn through the key switchA hose is connected to the fuel pump to monitor vacuumWhen the vacuum in this hose reaches the amount of mercury listed in chart below, the switch activates the warning horn continuously to indicate the fuel system is restricted If horn sounds, the fuel system may be restricted causing insufficient fuel delivery to the engine or the engine is overheatingIf horn sounds, back off the throttle until the horn stopsIf horn stops when throttle is reduced, this would probably indicate restricted fuel systemThe fuel system should be checked for restrictions as soon as possibleThe motor may be operated at reduced throttle if the horn stopsIf the warning horn does not stop sounding when the throttle is reduced, this may indicate the engine is overheatedStop engine to check for cause of overheatCOB1209