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??? on adjusting the fuel/air mixture on an outboard motor

Discussion in 'Boats and Motors' started by tech187, Jun 1, 2005.

  1. I have a 8hp Johnson 2 stoke outboard that starts ok, but does not seem to me like it every runs at top speed. It does not foul plugs often,but when I take them out they always look fouled. From what I have read I might need to lean down my fuel/air mixture. Do you do this while the engine is running and if so do you do it at wide open throttle or while idiling? Thanks for any help.
  2. Clarify what your plugs are fouled with to the people diagnosing. Then clarify what they mean by "leaning out" the mixture. The plugs may be fouled with oil, indicating too much oil in the mix. The "leaning out" that your hearing may therefore be people stating to put less oil (lean out) your mix.

    If the motor starts and idles well the main/idle mixture is good and should not be touched. Many smaller motors have a high speed adjustment as well, and if the mixture needs adjusted for the top end here is where you do that, as the idle circuit is by-passed when the motor is off idle. All carb adjustments should be done with the motor running at operating temp. With an 8 HP outboard, I would recommend backing the boat into a ramp so the motor is in, but do not undo the tie-downs. Run the motor to warm it up, and then do your adjustments on the trailer not moving, rather than trying to do it bouncing across the water at speed. I suggest a lake because you are not suppose to throttle motors up on ear muffs,, and this way you and anyone will be a safer distance from the prop! Good luck.

  3. Another thought is that your prop might be preventing the motor running at top speed.
  4. I put new plugs in and a week later I decided to take a look. They were coated with what has to be oil. The gas/oil mixture is 50:1 which is exactly what the owners manual calls for. The reason I think I need to lean out the fuel/air mixture is, a few days ago I had a piece of dirt or something get stuck in the carb and while the carb was running out of gas the motor ran better than I have every heard. It ran like what I think it shoud. The repair man at a Johnson dealer said it did that because it was leaning out. I know I can't lean it out to much, but I thought it might be a good idea to lean it out a little. Thanks for the response.