Adjusting the carburettor on a Yamaha outboard motor is a straightforward process. Even though it is straightforward, it may leave you feeling like you've spent a great deal of time standing on your head since the adjustments will require you to lean over the top of the motor for at least half the time it takes to make them. Fortunately, such adjustments are usually only necessary after the throttle body or throttle linkage has been replaced.
Loosen the cam follower roller screw, allowing the follower to move without restriction.
Locate the idle stop screw, located halfway down the throttle lever, and loosen its locknut.
Rest the roller on the throttle cam and turn the idle stop screw until the curved front edge of the throttle cam aligns with the centre of the roller. Re-tighten the idle stop screw locknut.
Hold the throttle arm against the idle stop. Reposition the cam follower so that there is a gap of between 0.00 inch and 0.10 inch.between the roller and throttle cam. Hold the cam follower in this position and re-tighten the cam follower screw.
The throttle linkage is all located on the port side of the motor. The throttle cam and cam follower are at the front port side, just in front of and above the separator tank, attached to the side of the throttle body. They look like a "rounded triangle," with the linkage -- the follower -- protruding from them. The throttle arm is almost halfway back on the port side, a hooked metal piece with a small screw protruding from its forward edge, directly behind the vapour separator tank and the idle stop screw is about three-quarters of the way down the throttle lever. The screw is threaded horizontally with the head facing forward and the thread facing aft.
Disconnect the negative cable of your battery before performing any maintenance work on your outboard motor, to prevent electrical shock or accidental starting. Remove the nut from the negative post with a 5/16-inch box-end wrench. Lift the cable from your battery, move it outside of the battery box and close the lid of the battery box. If you work on your outboard motor when your boat is on its trailer, or your motor is on a storage stand, remove the propeller nut with a wrench and slide the thrust hub, propeller and washers from the propeller shaft. Failure to remove a propeller before operating an outboard out of the water during maintenance or long-term storage is an invitation to a propeller-strike injury, which can maim or kill.