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  • Tachometer Requirements

    Hello All.

    I'm keen to fit a tachometer to monitor engine speed on my J35TEL3EEM 35hp 3-cyl 2-stroke outboard.

    A genuine new item is beyond my budget, so I'm looking for a used unit.

    I have yet to see a genuine Johnson tachometer advertised locally here in Brisbane, Australia. But tachometers for other makes, as well as generic units, are much more common.

    What do I need to know to avoid buying something incompatible? I know alternator pole count is important, but how many poles does my alternator have?

    Any other trap to be aware of?

    Thanks.


  • #2
    A bit of info here BUT no direct answer to your question.

    Normally "all" of the Evinrude & Johnson engines called for a tachometer that functioned off a "6 Pulse" charging system... but as time went by, I became aware that some of the smaller hp engines (even including a few of the 50hp models I think?) were supplying only 5 pulses. That leaves me to question just exactly how many poles your engine has to supply how many pulses, However.............

    On the back of the tachometers I was accustomed to using (Evin/John Dealerships) which are still readily available, there is a dial on the back of the tachometer whereas you can set the tachometer to whatever pulse required to operate properly.... no doubt available here on this site and elsewhere.

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    • #3
      You will need to find a tach with a 5 Pulse or 10 Pole setting, I don't know of any other outboard that uses that setting so you will need a Evinrude, Johnson or an aftermarket tach.
      Regards
      Boats.net
      Johnson Outboard Parts

      Comment


      • #4
        Thanks gents. I had my eye on a Mercury BNIB tacho for $40. But it is for a 12 pole alternator so unsuitable.

        Comment


        • #5
          I've purchased a used OMC tachometer # 0177107. It has the integral System Check LEDs. I suspect it's a dud, but not 100% sure.

          When switched to "On" at the key switch, the LEDs light and sequence to off as they should. But the tacho needle itself doesn't indicate proper speed. It points to around 6200rpm when off. It arrived in this condition. When the engine is running, the needle barely moves but goes up to around 6400rpm. Obviously not right

          When the engine is running and using a cheap as chips digital volt meter, I see 7.7V AC and 6.7V DC between the grey tacho signal wire and ground. Is this normal? When the DVM is set to Hz, I see around 105Hz. Strangely/coincidently this is 6300rpm by basic calculation i.e. 105 cycles per second x 60 seconds per minute. I believe my alternator is a 12 pole unit (but could be 10?). So at idle, the 105Hz should show 1050rpm on the tacho i.e. 105 x 60 / 6 = 1050.

          The tacho could be a dud but I is there some definitive test? I could have a wiring continuity problem??

          Any tips?
          Last edited by brw0513; 02-03-2019, 07:45 AM.

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          • #6
            Originally posted by boats.net View Post
            You will need to find a tach with a 5 Pulse or 10 Pole setting, I don't know of any other outboard that uses that setting so you will need a Evinrude, Johnson or an aftermarket tach.
            brw0513.... In essence, Boat.net has advised you (as above) that your engine has a 10 pole alternator and requires a tachometer dial being set to #5 (5 pulses). If Boat.net is correct and I strongly believe they are.... a 12 pole tachometer isn't going to be compatible with that engine.

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            • #7
              Hi Joe.

              I forgot to say I tried the tacho on the 5 pulse setting initially based on the information learned here. No difference I'm afraid.

              There are some credible sources that state 6 pulses is the correct setting too. The OMC printed instructions for the tacho state 6 pulses (since my outboard has two yellow stator wires) and the tacho came set that way and was apparently used on an engine identical to mine. The 5 vs 6 setting should(?) only make a difference to indicated rpm.

              I was wondering if there was some diagnostic process that could performed e.g. ground pins A, B, C and apply 12V to pin D and the indicating needle should sweep over the entire range etc.

              Comment


              • #8
                There should be a "Gray" wire attached to the terminal strip on the engine which leads to the wiring harness end at the control box or console.... that would be the wire that would attach to the sensor (S) terminal or sensor lead of the tachometer.

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