How to Adjust Idle Mixture Screws on a 2-Cycle Outboard Motor
- 1). Turn the idle adjustment screws clockwise with a screwdriver until you feel a slight resistance without over-tightening the screws. Turn both screws back counterclockwise 1-1/4 turns to set the starting position for the adjustment on the 2-cycle outboard motor.
- 2). Start the motor and let it warm up for about five minutes. Remove the rubber vacuum hose from the vacuum port and attach a vacuum gauge to the port.
- 3). Adjust the idle stop screw on the side of the carburetor near the choke cable, turning the screw with a screwdriver until the vacuum gauge is reading about 600 rpm.
- 4). Turn the idle mixture screw counterclockwise 1/4-turn at a time until you hear the engine begin to stall out, and turn it clockwise 1/4-turn.
- 5). Adjust the idle mixture screw by turning it clockwise 1/4-turn at a time until it starts to stall again and turn it back counterclockwise 1/4-turn.
- 6). Repeat Steps Four and Five for the idle air speed screw. Check the idle stop screw next to the choke and verify it is still running about 600 rpm.
- 7). Remove the vacuum gauge from the vacuum port, reattach the vacuum hose and shut off the 2-cycle outboard motor.