How to adjust idle mixture screws on a 2-cycle outboard motor

Written by carl pruit
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Routinely adjusting the idle mixture screws on a 2-cycle outboard motor will keep the engine running efficiently and provide power when you need. The 2-cycle outboard motor has two idle adjustment screws on the top of the carburettor that can be adjusted with just a screwdriver and a vacuum gauge. You can fine-tune the idle mixture screws in a few minutes and keep the motor running strong.

Skill level:
Moderately Easy

Things you need

  • Screwdriver
  • Vacuum gauge

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  1. 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. 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. 3

    Adjust the idle stop screw on the side of the carburettor near the choke cable, turning the screw with a screwdriver until the vacuum gauge is reading about 600rpm.

  4. 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. 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. 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 600rpm.

  7. 7

    Remove the vacuum gauge from the vacuum port, reattach the vacuum hose and shut off the 2-cycle outboard motor.

Tips and warnings

  • To avoid burns, be mindful of the hot engine parts while adjusting the outboard carburettor.

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