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Thread: 4age smallport on carbs

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    Default 4age smallport on carbs

    im converting my 4a to twin webber carbs and planning on using the msd 6al-2 programable ignition. i have read that i can use a bluetop dizzy and am currently looking for one. just curious as to why i cant use the smallport dizzy? i have searched everywhere!

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    I think it has something to do with the amount of wires on the dizzy itself?

    BP/Bluetop = 3 wires

    Please correct if incorrect

  3. #3
    Senior Member Hen may possibly be a nut's Avatar
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    The sensors in the guts of the two differ.

    Bigport/bluetop/3wire - Has a pickup which gets 24 pulses per cam rev, and one that gets 4 per cam rev.
    Smallport/whatevertop/4wire - Has a pickup which gets 24 pulses per cam rev, one that gets 1 per cam rev and a third which also gets 1 per cam rev, but is offset by 180? degrees (may be 90, would have to check) to the first.

    I can't see why a smallport dizzy wouldn't work, unless the MSD is hardwired to expect the inputs a bigport dizzy gives.... OK, just went and did some reading on them and it looks like the MSD just gives a spark every time the dizzy sensor gives a pulse. So therefore a bigport dizzy is needed (4 pulses per cam rev = 4 cylinders firing). The MSD unit seems pretty basic for configurability.

    Another option is to use the 24 pulse sensor in you smallport dizzy, but just cut all but 4 teeth of the sensor wheel. Bang, 4 pulses per rev for $0.

    Hen

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    i will just get bluetop dizzy. save me the mucking around, thanks alot hen

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