1995 Mariner Mercury Outboards Service Manual 50HP 4-Stroke, Page 59Get this manual
3Connect the vacuum gauge to the adaptors 4Run engine until it is completely warmed Turn the idle adjustment screw on #4 carboto obtain an idle of 1000 50 RPM
5Lightly adjust synchronizing screws #1#2and #3 to obtain the appropriate vacuum at each cylinder #4: base #3: #4 +1 cm Hg #2#4 +2 cm Hg #1: #4 +3 cm Hg
Example: If #4 reads 32 cm then ,
#3 reads 33 cm #2 reads 34 cm #1 reads 35 cm
6Rev engine two or three times and let idle for 15 secondsCheck to see if the vacuum at each cylinder has not changed by more than cm Hg 234