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Troubleshooting With Vacuum Gauge
Reading
Cause
Steady reading between 15-21 inches at idle
RPM
Normal
Extremely low reading, but steady at idle RPM
Vacuum leak; incorrect timing; underpowered
boat; faulty boat bottom
Fluctuates between high and low at idle RPM
Blown head gasket between two adjacent
cylinders
Fluctuates 4 or 5 inches very slowly at idle RPM
Carburetor needs adjustment; spark plug gap
too narrow;valves are sticking
Fluctuates rapidly at idle, steadies as RPM is
increased
Valve guides are worn
Continuously fluctuates between low and normal
reading at regular intervals at idle RPM
Burned or leaking valve
Index
90-823226--1 996
TROUBLESHOOTING - 1C-19