Mercury - Carburetor Adjustments

Outboard Motors
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Carburetor Adjustments

NOTE: After idle speed is set, the index mark on the throttle cam may not align with the pickup roller. This is normal.
Adjust the carburetorfor better starting and low speed operation. Changes in temperature, humidity, or barometric pressure can effect performance.
IMPORTANT: When adjusting the idle mixture screw, turn carefully and gentle. Do not force needle into seat.
1. Turn idle mixture screw clockwise until it seats in the carburetor.
2. Open idle mixture screw 1-1/2 turns (counterclockwise).
3. Start motor and warm up to operating temperature.
4. Move throttle lever to shift position.
a - Idle Speed Screw
5. Shift motor to forward gear and turn idle mixture screw (close) to the lowest “runable setting”.
6. Slowly turn idle mixture screw counterclockwise until motor speed decreases and operation becomes rough due to over-rich mixture. Note position of screw.
NOTE: Engine should NOT be running when making the following adjustment.
1. Shift motor to forward gear position.
2. Advance throttle to wide open throttle position.
3. Check throttle shutter position. THROTTLE SHUTTER MUST BE HORIZONTAL.
4. If throttle shutter is not horizontal adjust screw on throttle linkage (a) as shown until shutter is horizontal.
a - Lean b - Rich c - Correct Adjustment Point d - Idle Adjustment Screw
7. Slowly turn idle mixture screw clockwise: motor operation will become smooth and speed will increase. Continue turning idle mixture screw clockwise until motor speed slows or misfires from too lean a mixture. Note screw position.
8. Turn idle mixture screw to midpoint between settings noted in steps 6 and 7.
a - Adjustment Screw
Return throttle to idle position and shift engine to neutral.
NOTE: Idle speed should be 750 RPM.
1. Shift into gear.
2. Adjust idle speed screw (a) to proper idle rpm.
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