How to Adjust the Carb on a 9.9 Evinrude

Written by adam paul
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Many power boats are equipped with an Evinrude 9.9-hp outboard engine, as this size is a good compromise between price and power. Like all engines, the Evinrude 9.9 tends to get out of tune as the boating season progresses. New outboards generally have self-adjusting carburettors, but on older ones you have to manually adjust the carb. Fortunately this is very easy, and you can make the adjustments without even pulling the boat out of the water.

Skill level:
Moderately Easy

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  1. 1

    Run the boat and the outboard for 10 to 15 minutes to warm them up.

  2. 2

    Bring the boat to an open stretch of water and throttle up to full power. Turn the screw marked "high" on the front of the outboard either clockwise or counterclockwise, no more than a quarter turn, until you hear the outboard rev higher. Once you determine the screw position that indicates the highest idle, turn the screw counterclockwise just a little bit to enrich the mixture and prevent the engine from burning too lean. This sets the high-speed jet on the carburettor.

  3. 3

    Drive the boat to the dock and tie it up. Place the outboard in neutral and leave the engine running. Throttle it all the way down until it stalls. If it does not stall, adjust the screw marked "slow" to achieve the highest idle. If it stalls, alternate a quarter turn clockwise and counterclockwise until you get it to idle. Once it idles, adjust for the highest idle.

Tips and warnings

  • Use fresh gasoline, and make sure that the fuel filters are not clogged. If the engine is not running properly, you may have a problem with the fuel pump.
  • If you don't have a tiller-controlled outboard, have an assistant steer while you adjust the carburettor.

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