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Thread: Tach help, Low Idle Readings

  1. #1
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    Default Tach help, Low Idle Readings

    Have a 3cyl 25hp that I picked up, installed 1 tach, readings at idle are 350-400rpm. I didn't think the tach was working correctly so I bought a different brand with a ground and I am getting the same readings.

    Attached to the 3rd plug, 5wraps, settings are 3P1R.

    Motor has been worked on some, MD40 carbs, reeds, shaved heads.
    Does this sound low or are both the tach reading correct?

    For reference, boat runs great at flounder trolling speed but when I ran it up, says motor only is turning 1710 but running about 30mph. This also doesn't seem correct to me.

    I got the tach to fine tune prop. It's a Yamaha black stainless 13-p.
    Last edited by scdiver; 07-12-2018 at 09:07 AM.

  2. #2
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    There should be a place on the back of the tach to change the setting. My be just a little tab you slide over
    or another post to attach the wire to. That is your problem, very common
    "I am going to plead with you, do not cross us. Because if you do, the survivors will write about what we do here for 10,000 years"


  3. #3
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    Try wrapping the tach wire around just once. When I had my tach installed on my F40 and the wire was wrapped several times it would give me funny readings. A friend told me to wrap it just enough for the wire not to fall off and that fixed my issue.
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  4. #4
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    Quote Originally Posted by CUduckreeper View Post
    Try wrapping the tach wire around just once.
    This. If that don't work then you need to change the spark per revolution setting on the tach.

    Sent from my SM-G930V using Tapatalk

    Delta in a nutshell: Breeding grounds + small wetlands + big blocks of grass cover + predator removal + nesting structures + enough money to do the job= plenty of ducks to keep everyone smiling!

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  5. #5
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    What should the setting be for a 3cyl 2stroke? The package said 3P1R. I wrapped it once, will let y'all know how that works.

    Thanks for the help.

  6. #6
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    Quote Originally Posted by scdiver View Post
    What should the setting be for a 3cyl 2stroke? The package said 3P1R. I wrapped it once, will let y'all know how that works.

    Thanks for the help.
    sometimes you just have to play with the setting selector. I have had to try different settings til I see 750 rpm or so idling and then I know its most likely the correct one.
    "I am going to plead with you, do not cross us. Because if you do, the survivors will write about what we do here for 10,000 years"


  7. #7
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    10-4, thank you.

  8. #8
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    Honestly I can't remember what the setting is. I think it's 1 spark per revolution. I'm talking Tiny Tach's here.

    Hopefully the loop thing works. My 3 cyl Yamaha also wouldn't work right until I did just one small loop around plug #3's wire. Trimmed the rest off after that. Had no problems since.

    Sent from my SM-G930V using Tapatalk

    Delta in a nutshell: Breeding grounds + small wetlands + big blocks of grass cover + predator removal + nesting structures + enough money to do the job= plenty of ducks to keep everyone smiling!

    "For those that will fight for it...FREEDOM...has a flavor the protected shall never know."
    -L/Cpl Edwin L. "Tim" Craft

  9. #9
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    Nice looking new sled!
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  10. #10
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    Quote Originally Posted by willk View Post
    Nice looking new sled!
    Thanks man, hopefully catch a pile of flounders on it over the years. Already broke it in!

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