Idle Speed Adjustment 40 HP Yamaha Outboard
The following service procedures are for the 1998 40HP Yamaha outboard 2-stroke model. Procedures may be exact or similar for other models such as the 1999 2000 2001 2002 2003 2004 2005 and 2006 engines. Regardless, never attempt to service any motor without a repair manual to guide you through servicing procedures.
Idle Speed Adjustemnt
NOTE: Make sure the idle speed is adjusted before you adjust the throttle link.
- Measure the idle speed, if the idle speed is not within factory specifications, adjust.
Idle speed factory specifications: 800 +/- 50 rpm.
- Turn the engine on and allow it to come to normal operating temps.
- Attach a tachometer to the high tension lead of cylinder number one.
- Fully close the throttle valve by loosening the idle adjusting screw.
- Loosen the throttle lever securing screws located on the upper and middle carburetors, you will turn the screws clockwise.
- Rotate the pilot screw inward until it is lightly seated.
- Now turn the pilot screw outward until you meet specifications. Pilot screw (turns out) specifications: 40 HP = 1-1/2 +/- 1/4
- Turn the motor on and allow it to reach normal operating temps.
- Connect the tachometer to high tension lead of cylinder number one.
- Make adjustments to the throttle stop screw, turn the screw in or out until the specified idle speed specs have been meet. Turning in, the idle speed will become higher. Turning out, the idle speed decreases.
- While carefully and lightly pushing the throttle lever on the lower carburetor in the direction of the arrow (fully closed), begin to torque the throttle lever securing screw located on the middle and upper carbs by turning the screws counterclockwise.
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