Rev counter reading double

Discussion in 'UK Motorcycles' started by Whinging Courier, Sep 4, 2006.

  1. Right, the ratbike's had a makeover. I've cut the front subframe off,
    put the headlights on the forks, rewired and added some new
    blingdictaors and fitted the chrome[1] speedo and tacho.

    Now, with a little faffing about and trial and error, I've got
    everything working properly except the tacho, it's reading I guess
    double what it should - This wouldn't be a problem as I could half the
    revs but it only goes to 15,000 rpm and my bike redlines at 10,5000rpm.

    Now, I wired it into the existing loom because I thought his would be
    easier and save messing around taking the tank off to connect it to the
    negative side of the coil. Thing is, is there or would there be
    something in the Honda rev counter to make it read half what the new one
    is and how do I connect it to the negative side of the coil? There's
    four of them and there's no obvious negative side.

    I'm going to try running a wire tomorrow just to see but it'd be helpful
    if anyone could give me a clue as to what might be up and any remedy if
    the wire running doesn't work.


    [1] This will soon change with the addition of some exhaust paint
    Whinging Courier, Sep 4, 2006
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  2. Whinging Courier

    Pete Fisher Guest

    In communiqué <>, Whinging
    A quick Google suggests this is not an unknown problem when fitting a
    tacho from a different bike. Some ignition systems use a 'wasted spark'
    which could fool a tacho not designed for the bike or the number of
    coils may be different hence too many pulses.

    A relevant discussion which may shed light here:


    | Pete Fisher at Home: |
    | Voxan Roadster Moto Guzzi Mille GT/Squire RS3 Gilera Nordwest |
    | Gilera GFR Moto Morini 2C/375 |
    Pete Fisher, Sep 4, 2006
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  3. Whinging Courier

    Mups Guest

    Are you sure there are 4 coils IIRC there's only 2; one does cylinders 1
    and 4, the other 2 and 3. The rev-counter is probably counting each pulse
    as a firing stroke and I'm fairly certain that the fatblade has a 'wasted
    spark' system where the plugs fire on the exhaust stroke as well.

    How to fix it? **** knows. Is there anything you can set on the
    Mups, Sep 4, 2006
  4. In, Pete Fisher belched forth and ejected the
    A couple of things...

    First, one bloke talks about a tweakable pot. I did notice a gromit type
    bung in there and thought it was the bulb. I'll check that tomorrow.

    Also, someone talking about a Mito saying when they used the HT wire it
    read double but when they used another one it read true.

    I don't know if there is another wire but as that was the first one I
    tried and it appeared to work, that's the one I used.

    I had to pack up in a hurry because it was getting dark but I'll have
    another look tomorrow, cheers.
    Whinging Courier, Sep 4, 2006
  5. In, Mups belched forth and ejected the following:
    Yes, you're quite right. There's two :)
    I'm not sure.

    What I thought was a bulb might not be. There's a thing with a small
    screwdriver sized hole in it. It could either be a bulb or a thing to
    calibrate it.
    Whinging Courier, Sep 4, 2006
  6. Whinging Courier wrote
    Pictures man, where are the fucking pictures?
    steve auvache, Sep 4, 2006
  7. In, steve auvache belched forth and ejected the
    Patience man!
    Whinging Courier, Sep 5, 2006
  8. Whinging Courier, Sep 5, 2006
  9. Whinging Courier

    Moon Badger Guest

    I fitted that setup to my GTRat. I hooked the pickup wire from the tacho on
    to the original tacho feed in the loom. The unit I bought was for a twin, I
    figured thats what I needed with the wasted spark ignition. Did you buy the
    one for a four cylinder bike?, if so, the wasted spark ignition might be
    the cause.

    Must finish the rat. Need to attack the back end ( of the bike ) with an
    angle grinder, though it does look kinda nice/sweet/shyte ( delete as
    applicable ) with its luggage on and that front end.
    Moon Badger, Sep 5, 2006
  10. In, Moon Badger belched forth and ejected the
    That's what I've done.
    I bought one "for a Honda".

    I don't think there's any difference; the instructions say attach the
    green wire to the negative side of the coil. There is no negative side,
    just that pickup wire you mentioned.
    Being able to put luggage on is a good thing.

    You could always attack it and rebuild it to look completely different
    but luggage friendly.
    Whinging Courier, Sep 5, 2006
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