Re: Syncing carbs on 1978 115 mercury
They do not use vacuum gauges to sync the carbs. There are adjustments on the black plastic rods that connect the carbs butterflies together to assure the carbs open together. Make sure those are set correctly. Set the idle mixture screws 1-1/2 turns open, and warm the motor and adjust for best idle, in the water and in gear if possible.
Now the carbs are set too lean, but synched. Now try to accelerate. If she stumbles, open top carb 1/8 turn and try to accelerate again. If she still stumbles open the mid carb screw 1/8 turn and repeat test. Open bottom screw 1/8 turn and retest. Now repeat sequence until you have good, smooth acceleration and reasonable idle at 850RPM or less in gear.
