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early 90s yamaha 40 hp 3 cyl

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  • early 90s yamaha 40 hp 3 cyl

    when I start it up it revs up quit high then after half min or so it idles right down to normal rpms. the other issue im having is that after it idles down some time it stays running and some times it quits ones it idles down. if it does die it starts right back up don't have to choke it or anything just fires right up so I don't know whats going on because I just cleaned the carbs and it doesn't seem to be a fuel issue more of electrical. I have spark on all cyls. if u have any idea please let me know. thanks

  • #2
    Re: early 90s yamaha 40 hp 3 cyl

    Does this motor have a choke or is it a prime start model?
    Prime start motors advance timing for cold start and drop to normal idle timing when motor warms up

    Did you follow the steps in service manual for adjusting everything after reinstalling the carbs?
    Needs to be done each time they are reinstalled

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    • #3
      Re: early 90s yamaha 40 hp 3 cyl

      i set them all the cards back to the same float drop and adjustments that they were when i pulled them off. the reason i cleaned them is because the motor was boggy and would hardly
      run.

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      • #4
        Re: early 90s yamaha 40 hp 3 cyl

        If it runs fine at higher RPM's and just not in idle, then it's most likely fuel related. You either didn't clean the carbs well enough (particularly the idle circuit in the carbs), or they got gunked up again, or you didn't follow the link and sync procedure in the manual when reinstalling them, or you need to adjust the idle speed screw.
        My guess is that the idle circuit in the carbs is compromised. Soak the carbs this time.

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        • #5
          Re: early 90s yamaha 40 hp 3 cyl

          I will repeat one more time
          Originally posted by 99yam40 View Post
          Did you follow the steps in service manual for adjusting everything after reinstalling the carbs?
          Needs to be done each time they are reinstalled

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          • #6
            Re: early 90s yamaha 40 hp 3 cyl

            i had the card in a card bath for a hour each i set them to the book specs i didn't do a sync and link do to it ran good and wasn't adjusted since the last time it was synced. it will run at high rpms but not idle. sometimes it will stay running and other times it will just quit.

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            • #7
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              Re: early 90s yamaha 40 hp 3 cyl

              its a 1989 actually

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