OEM Black box alterations

[Mary or Stephen Burgess]

This is'nt exactly efi related, but none the less, it travels down an avenue
most of you already have.

I have, against better advice, taken apart the hermetically sealed ignitor
box on my yamaha motorcycle, looking for dip switches, potentiometers, or
any secret method of altering the stock ignition timing. (I'm one of those
people that if they say it can't be done, I've got to try it on my own and
see if I can proove them wrong)

Anyhow, imagine my shock, when I found NASA mission control embedded into a
small circuit board, and a Hitatchi microchip that could probably give an
old IBM XT a run for it's money. 

No, I did not find any dip switches, or potentiometers, though I was hoping
for a small note that said "to change ignition timing turn this knob
clockwise=advance, anticlockwise=retard" :-)

I did find an unused circuit on each of the two bipolar transistors that I
believe could be of some interesting use. I have identified the "unused"
circuits as R/C integrators with a resistor and capacitor fixed in a
parallel with the base trigger and output of the R/C integrator is connected
to the collector. 

I'm no genius when it comes to electronics, but what it looks like to me is
that this "unused" circuit has one of several functions. 

- to eggagerate ringing in the ignition coils and effectively create a
multiple spark ignition.

- to counteract impedance in the coils, and effectively eliminate ringing in
the igntion coils.

- to advance ignition by the amount of time it takes to charge the capacitor
(based on a function of both resistance and capacitance - R-C time constant???)

I looked at this for quite some time, and I think the bipolar transistors
are being used as filters, a saw tooth signal is sent to the base, and as
the frequency of the sawtooth increases it's amplitude decreases,
effectively creating a rev limit when at 12500 rpm the amplitude of the
sawtooth is insufficient to trigger the transistor i.e. less than 0.5V

- the R/C circuit could also serve a function of increasing rev limit with a
small capacitor adding a "second cap" on the sawtooth and increasing it's
amplitude.

Like I said I'm no electronic wizz, and it took me days to come up with a
few speculative guesses as to it's possible uses, and so with no sure way to
decide (replacement units are $300, and it has to come from Japan so there's
a 4 month wait - try it and see is out!!!) I am consulting those of you with
actual electronics background and experience with this type of thing (that
is altering stock ignition modules)

I tried to describe the circuit as best as I could, but I have drawn it out
if anyone does'nt immediately recognise it's purpose, and want's or needs to
see it, I can attach it to an email to that person, I don't want to upload
pictures to the list, especially since it's not directly related to efi.

Type to you later!
Steve

----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org