Yamaha F100B F100C Outboards Factory Service Manual, Page 91Get this manual
Carburetor Synchronizing the carburetors
1Start the engine and warm it up for minutes to check the stability of the engine2Attach the special service tool to hightension cord #1 1#1 #2 #3 #4
S60C4290
Digital tachometer: 90890-06760 3Remove all of the plugs and attach the special service tool and adapters to the carburetor assembly as shown
S60C4330
Vacuum gauge (digital) (commercially obtainable) 3: Vacuum gauge (4 analog meters) (commercially obtainable) 4: Vacuum gauge adaptor (commercially obtainable) 5: 4Adjust the idle speed to 1,000 rmin by turning the throttle stop screw on carburetor #4 in direction or b