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Hooking up a tach and dwell meter

Discussion in 'The Garage' started by ExSquid, May 7, 2019.

  1. ExSquid

    ExSquid XS650 Member

    Greetings from Green Bay,
    As a Navy diesel mechanic, we don't use tach and dwell meters or timing lights. It seems that the light is straight forward. Battery power and left plug wire. So where do you hook up the tach and dwell meter? I know on my older cars its the signal from the distributor. Do I have to find "that secret wire"?
  2. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Red wire goes to the points, black to ground.
  3. 5twins

    5twins XS650 Guru Top Contributor

    Personally, I don't use the tach feature much, if at all, but I do use the dwell function all the time. It's the only way I set points gaps now. So yes, hook the meter's red lead to the points set wire (I clip it to the little bolt holding the wire), black to ground (I use a cylinder fin), like so .....


    Be sure the red wire connection is isolated to only the points wire. It can't touch anything else like the rest of the points set, the backing plate, or the housing. You will need to connect it to each points set individually to set each one. Now let's talk about the dwell value. It is given in the shop manual and is 93° ± 5°, or 88°- 98°. Now, this is the 2 cylinder value that you'd read on a 2 cylinder dwell meter, but I've never even seen one of those. Most likely you will be using an automotive type with 4, 6, and 8 cylinder settings. The reading you get will be a little different on those scales and we need to do a little math to figure out what it will be. The lower the scale, the more accurate the reading will be, so use the 4 cylinder scale if you've got it. On the 4 cylinder scale, you divide the 2 cylinder value by 4 (for these dual points). So that means you'll be looking for a reading of between 22° and 24.5°. Now, the reading you get on a dwell meter is inversely related to the points gap size. That means a larger reading indicates a smaller gap, smaller reading a larger gap. I try to set the points as close to the smaller number as possible so I get the largest in-spec gap as possible. As points wear, their gap usually closes up, so I figure they will stay in spec longer if set to the larger gap.
    OHRider and TwoManyXS1Bs like this.
  4. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Hey sailor... just had a memory jog...... don't you have a TCI iggy? If you do there's no point in checking dwell. It's baked into the electronics.... non-adjustable.
    Mailman and TwoManyXS1Bs like this.
  5. ExSquid

    ExSquid XS650 Member

    I do have the TCI unit. You still have to use a tach because "the bike's tach is unreliable", so I've been told.
    Mailman, gggGary and Jim like this.
  6. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Gotcha. Don't worry, you'll develop an ear for the rpm.... ;)
    Mailman likes this.
  7. ExSquid

    ExSquid XS650 Member

    Aye, Aye!
    OHRider, Mailman and Jim like this.

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