Lotus Elan

123 Ignition Tune

PostPost by: billwill » Fri Dec 06, 2013 1:07 am

A nice, useful report.
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PostPost by: vernon.taylor » Mon Dec 09, 2013 7:10 am

Salut Vernon(2)

Yes, I'd be very interested to see some pictures.

Did you use both the restrictor and vacuum chamber ?

Merci et @+

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PostPost by: quaybook » Thu Dec 12, 2013 12:39 pm

Sorry for slow response, new grandchild (my daughter has named her Elise after her beloved lotus) meant a few days away from base.
Yes, I've used both restrictor and reservoir. The restrictor was almost enough on its own, but not quite. Using a small fuel filter as a reservoir as well as the restrictor resulted in a steadier vacuum than the length of larger diameter tube I finally used, but looked clumsy. The DHLA idle jet I used as a restrictor was a good tight interference fit in the 5mm id vacuum tube, it needed petroleum jelly lubrication to get it in. It is located in the vacuum tube just beneath the tee joiner in the photo.
Hope I've uploaded the photo correctly!

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PostPost by: nmauduit » Wed Feb 18, 2015 3:02 pm

I was wondering if more people had tried the 123 route for distribution since the start of this thread... and would be interested in their feedback and possibly tuning advice.

After reading several of the forum dizzy threads (and the always increasing release delay of the cheaper Pertronix ignitor3 alternative), I have reached a decision and one of their Kent model (2 programmable curves) is on its way to my street elan, hopefully for more reliability through performance optimization (I believe a smoother running engine last longer).

While I wait, I'm considering an issue that remains : this car has a weber head, and vacuum signal does not seem to allow for adequate load assessment. I've exchanged with Frank from Albertronic (123 NL) about converting the MAP input into an TPS input. Here is the essence of his replies :
The vacuum sensor we are using is 5 Volt analogous.

This means:
1,0 Volt is -1 Bar
2,5 Volt is 0 Bar
4,0 Volt is + 1 Bar
or something like this....

If you think you can make something that makes this Voltage out of a TPS it should be possible.
Please don't expect any technical support from our side.....

I understand their MAP sensor is integrated to the dizzy, so at this point a modification would entail voiding the warranty...

Typical weber TPS (cf. Webcon etc.) are 5k Ohm potentiometers, and with 5VDC applied would typically output a throttle range giving ~0.8V to ~4.5V (closed throttle 900 Ohms and WOT 4500 Ohm to ground).

To compress and translate that it should be sufficient to add a resistor between the ground and the TPS, in the example above for instance 1400 Ohm between ground and TPS ground, and 5000 Ohm between 5VDC and TPS power (advantage of using only passive components). This would give approx :

closed throttle 1V
WOT 2.6V

A coaxial cable should be used, coming from the distributor where it should be grounded and possibly carrying 5VDC in addition to signal coming back from the TPS (twin coax).

Then a suitable TPS advance curve will have to be determined, from trial or rolling road experiments.

This seems straightforward enough for me to be tempted in spite of voiding the warranty, and I'd be surprised that such a tweak has not been already considered...
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PostPost by: nmauduit » Thu Apr 16, 2015 7:12 pm

Here is the modification I have done to the 123 distributor now installed in my elan :

123 modified for TPS.JPG and

The active pin of the vacuum sensor (Freescale MPXH6250A) has been unsoldered and lifted (pin 4, bottom left of the row of 4 on the picture), so that the active lead (white) of a small coax can be soldered to drive the pcb instead, with the ground soldered to a nearby pad. An other coax (red active lead) is used to get a +5VDC reference from the pcb, taken out from the other side of the board as per Albertonic's suggestion (they provided the picture below to that end).

TPS hook second version.JPG and

Since the pads are small and the pcb not designed for these extra soldering points, I have attached and glued the two small coax to existing wires for stress relief. Both small coax have been routed through the existing hole together with the 4 original wires.

A TPS sensor (from Webcon, a potentiometer of about 5 kOhm impedance) has been attached to the front weber, using a second support point from a bracket attached to the bottom since this old carb did not have the bossing for a second tapered hole today's carbs have.

sensor setup on bottom bracket.jpg and

With respect to the Alpha instructions, the TPS is used in reversed polarity (that is +5VDC on 1 / ground on 2 / signal on 3 of the TPS connector), so that it mimics the MAP sensor it is meant to replace (closed throttle corresponding to more vacuum).

Once hooked up, the TPS input give approximately the following readings :

closed throttle 0.08V which reads as -0.95 Atm MAP unit
WOT 1.92V which reads as -0.30 Atm MAP unit

Now I've entered a first TPS curve, to be added to the "mechanical" advance curve I had set :

curve1.JPG and

Adding two curves is clearly not as flexible as a 3D map (e.g. at this point it cannot account for load differently according to RPM, so one should no go over board regarding load advance), but it opens the way to account for load without having to rely on weber vacuum signal, and provides an easy computer tuning and 2 sets of curves switchable live.

These curves are indeed to be optimized from trial on the road (e.g. using the stopwatch feature of the 123 software, though traffic is rather dense nearby so I have to go several tens of miles away just to be able to park on the side of the road and do some curve reprogramming) or rolling road when I get a chance - I still have some jetting to optimize first.

I'm not sure where exactly the improvements come from, but it starts quite easily now and idles smoothly (I had the feeling the old 23D4 produced some scatter). So far, so good...
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