Preliminary Idle Speed And Mixture; Final Idle Speed And Mixture - MerCruiser GM4 Service Manual

Preliminary Idle Speed and Mixture

IMPORTANT: The following adjustments will pro-
vide a sufficient idle speed and mixture for start-
ing engine. Final adjustments must be made with
engine running.
1. Back out idle speed screw until it no longer con-
tacts idle cam. Turn idle speed screw in until it just
contacts idle cam, then turn screw in an additional
two turns.
a - Idle Speed Screw
b - Idle Cam
IMPORTANT: DO NOT turn idle mixture needle
tightly against seat (in the following step), as
damage to seat and/or needle may result.
2. Turn idle mixture needle in until lightly seated,
then back needle out 1-1/4 turns.
a - Idle Mixture Needle
Index
90-816462 2-695
b
a
72284
a
72281

Final Idle Speed and Mixture

IMPORTANT: Boat must be in the water and en-
gine at normal operating temperature to accu-
rately check and adjust idle speed and mixture.
Carburetor should be set so that engine idles smooth-
ly within range given under "Specifications," with boat
in the water, engine at normal operating temperature
and drive unit in forward gear. To adjust idle speed
and mixture, proceed as follows:
IMPORTANT: DO NOT attempt to compensate for
other engine problems (incorrect ignition timing,
faulty ignition components, low compression,
vacuum leaks, etc.) with carburetor adjustments.
This will only cover the problem, which must be
corrected if engine is to achieve maximum fuel
economy and performance.
1. Connect an accurate shop tachometer to engine.
IMPORTANT: DO NOT turn idle mixture needle
tightly into seat, as damage to needle and/or seat
may result.
a - Idle Mixture Needle
2. If new or rebuilt carburetor has been installed,
turn idle mixture needle in (clockwise) until it light-
ly contacts seat, then back out needle 1-1/4 turns.
This will provide a sufficient setting to allow start-
ing engine.
3. Start engine and run at 1500 RPM until engine
reaches normal operating temperature.
! WARNING
DO NOT leave the helm unattended while per-
forming idle speed and mixture adjustments, fol-
lowing. BE CAREFUL NOT TO ACCIDENTALLY
ACCELERATE ENGINE WHILE PERFORMING
ADJUSTMENTS.
MERCARB 2 BARREL CARBURETOR - 5B - 9
a
72281