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  1. #1
    Petty Officer 3rd Class
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    Default HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    does anyone know the ht lead resistance readings for this outboard?
    i have 2 very different readings from my 2 ht leads and am trying to diagnose a misfire.

    When i pull the leads off the plug when idling i get a big shock!!


    thanks

  2. #2
    Captain pvanv's Avatar
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    What is your model? I assume you have an M25C3? Under what circumstances do you have a misfire? Sounds like you are getting spark to the plugs. What is the compression, and what are the plug conditions? Specific service data is in the Factory service manual, BTW.
    Paul
    Certified TLDI Technician
    Buffalo NY USA

  3. #3
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    Hi Paul
    my Tohatsu Model is M25C3 372 as you guessed.

    not sure on compression but last time i used the engine it had plenty of power and accelerated well.
    I am getting the misfire at idle but only really noticed it when trying to pull away from stationary. the engine chugged alot and when putting it back in neutral it was kicking side to side like it was firing then not firing.

    I have brand new plugs on order to eliminate them from the equation.

    I tested the resistance in the ht leads. One lead was reading 5.0 and the other was 0.01. Cant remember which k the dial was on but those readings are quite far apart.
    What reading should i get? is more resistance in the lead good or bad?


    Plugs are slightly black, a bit oily prob due to misfiring but not very dry or burnt.
    any help would be good.

    thanks

  4. #4
    Vice Admiral TOHATSU GURU's Avatar
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    You have to have a service manual to troubleshoot this model's ignition system. The test procedure values and the method used to perform the tests are outlined therein.
    Elvin
    My answers are like Zen...It may not be the answer you want, but it is generally the answer you need.

    The 3 Rules:

    1) Look in your service manual first...Then ask me if it is correct.
    2) Understand that your desire to repair your engine does not mean that you have the ability to do so.
    3) If you are confused, take your engine into a dealer..Then let them be confused...At least, in theory, they sent someone to outboard 101.

  5. #5
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    now where do i get one of those service manuals!!
    I find getting info on outboards tricky, unlike cars there are haynes manuals for everything with wheels

    Is there any pdf's on the net with it in?

    thanks

  6. #6
    Vice Admiral TOHATSU GURU's Avatar
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    Any Tohatsu or Nissan dealer...And any Mercury dealer can get one for you too. The test procedures and values are 4 pages long and you have to use an analog meter. The factory manual is only available as a paper copy to avoid copyright theft.
    Elvin
    My answers are like Zen...It may not be the answer you want, but it is generally the answer you need.

    The 3 Rules:

    1) Look in your service manual first...Then ask me if it is correct.
    2) Understand that your desire to repair your engine does not mean that you have the ability to do so.
    3) If you are confused, take your engine into a dealer..Then let them be confused...At least, in theory, they sent someone to outboard 101.

  7. #7

    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    Commando C2, I sent you a private message with some details. Did you get it?

  8. #8
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    here are some findings from tests


    1
    I tested resistance between the black and yellow wire(once disconnected from the cd box) and the earth on the coil and got 0.8. The manual/dealer said i should get 0.2-0.3 ohms.

    2- plug terminal to ground lead on coil; couldnt get a reading!
    i put one probe in the end of the plug cap and the other to various parts of the engine (earth/ground)
    Still no reading.

    i also Took off both plug caps from spark plugs.
    tested resisitence between plug caps
    (one probe in end of plug cap one and other probe in end of plug cap 2 )
    Reading. 9.80 on 20k setting on multimeter.

    I also Removed ht leads from coil and tested resistence between where each ht lead screwed into
    reading 4.81


    i think the coil may have died. Would the coil have got burnt out do you think from the main wiring loom from the magneto getting worn through by the clamp holder as this happened the other week and the wires were burnt and broken. I have since mended them but think the strain may have killed the coil or is that unlikely?

    i checked for continuity from all the magneto wires and to the cd box and they are good. so it is probably the cd or coil

    will update as it gets fixed!!!

  9. #9
    Vice Admiral TOHATSU GURU's Avatar
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    I think you need the correct manual. There are some 30 pages on the ignition system alone and it looks like you are using incorrect values and tests...There is no short cut to troubleshooting.
    Elvin
    My answers are like Zen...It may not be the answer you want, but it is generally the answer you need.

    The 3 Rules:

    1) Look in your service manual first...Then ask me if it is correct.
    2) Understand that your desire to repair your engine does not mean that you have the ability to do so.
    3) If you are confused, take your engine into a dealer..Then let them be confused...At least, in theory, they sent someone to outboard 101.

  10. #10
    Petty Officer 3rd Class
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    well i have the right manual and am looking at the info on the 25hp that i have.
    i think i may just sell the engine and go back to using my 1985 evinrude that has never missed a beat!

  11. #11
    Vice Admiral TOHATSU GURU's Avatar
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    What pages are you on for each of those tests? I will be happy to baby step you through the manual, but I need to know where you are in the manual so that you can follow me with a visual guide.
    Elvin
    My answers are like Zen...It may not be the answer you want, but it is generally the answer you need.

    The 3 Rules:

    1) Look in your service manual first...Then ask me if it is correct.
    2) Understand that your desire to repair your engine does not mean that you have the ability to do so.
    3) If you are confused, take your engine into a dealer..Then let them be confused...At least, in theory, they sent someone to outboard 101.

  12. #12
    Petty Officer 3rd Class
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    Okay,
    firstly i replaced the sparks for brand new gapped to 1mm.
    Took boat out. Knew straight away it was not running right.

    Replaced plug leads and plug caps. Ran engine and it was alot smoother and lifted the boat out of the water onto the plane, finally.

    The resistance of the new leads were 5.08 ohms and one of the old ones was o.o1 and the other was 5.0 so i assume it was the low reading plug lead. In the bin now.

    The engine doesnt seem to trawl very happily at idle speed compared to my 1985 year 25hp evinrude. The tohatsu needs about 1/4 throttle to smooth out.

    Anyone find this with their M25c3 ?
    Is it because of the cross charge or loop charge design? i cant remember which one is smoother at idle speeds.

    Maybe i need to clean the carb jets but then if it was mucky it wouldnt idle at all i guess!!

    Thanks for all your help esp TG for offers of going through the manual.

    Any info on the trawling characteristics of this engine would be helpful

    thanks

  13. #13
    Captain Sea Rider's Avatar
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    Default Re: HT resistance readings 25hp 2 Stroke Tohatsu 2000 model?

    My 18 horse can idle for a long period from 0 throttle to about where marks meets as when starting engine from cold, but when opened to 1/3 throttle engine purrs for some seconds and bang she goes fine. Seems when cruising at idle speeds, plugs have not reached proper working temperature, engine purrs a bit until oil on plug tips are completely burned when openning her at 1/2 to full throttle. So have skipped 1/3 setting, now only using idle, 1/2, 3/4 & full wot

    Happy Boating

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