2001 Mercury Mariner 50-60HP Factory Service Manual, Page 130Get this manual
TIMING, SYNCHRONIZING,ADJUSTING
Carburetor Synchronization
NOTE: The carburetors are synchronized by adjusting the intake manifold vacuum on the carburetorsUse Carburetor Tuner (91-809641A1) or Vacuummate Tuner (pn 91-809871-1) to measure the vacuumINSTALLING CARBURETOR TUNER 1Remove four plugs from the intake manifold2Install intake manifold hose adaptor in each plug holeTighten securely