Mercury 40 Service Manual page 129

Idle Mixture Screw Adjustment
NOTE: Idle mixture screw adjustment is required when stable idling could not be obtained
after synchronization.
NOTE: The engine should be completely warmed up for the adjustment. Correct adjust-
ments can not be obtained in a cold condition.
NOTE: The idle mixture screw is:
NOTE: Screw Adjuster (91-809906A1) is required to adjust the idle mixture screws on 45
hp models.
DYNAMIC ADJUSTMENT (50 HP MODELS) 1995-1997 MODEL YEAR
1. Connect tachometer.
2. With engine idling, turn the #4 carburetor idle mixture screw an 1/8 turn both directions
(clockwise and counterclockwise).
3. If the engine speed drops when turning screw both directions, leave screw at initial posi-
tion.
4. If the engine speed increases in one direction, keep turning it in that direction by 1/8 turn
increments to find the point of highest idle speed.
5. Adjust the idle mixture screw on the #1, #2 and #3 cylinders in the same manner.
6. Rev engine two or three times and let idle for 15 seconds, if a stable idle is obtained,
perform the Idle Speed Adjustment.
1
2
3
4
a -
b -
90-828631R3 MARCH 1999
Adjustable:
-All model years for the 45 hp version
-1995-1997 model years for all other versions
Non-adjustable:
-1998 model year and later (50 hp).
a
Remove Plug
Idle Mixture Screw
TIMING, SYNCHRONIZING, & ADJUSTING
b
Page 2C-7