Vacuum Advance on a 123Ignition-Installed Dino 246GT - Good Idea?

I recently installed a 123Ignition (Bluetooth enabled) on my Dino #4486. It was originally a 1973, but the luminaries at the California DMV insisted that to register it here in California, it should be a 1972 since the MFR data was Sept 1972. This is why you may see some older threads for this car as a 1973.


In any event, the distributor runs well but I continue to fight an occasional stumble that occurs just as I start opening the throttle. It could occur at 2000-4000 RPM in different gears but if push more on the throttle, the engine responds well and pulls without issue.


In my research, one possibility is the engine runs lean at almost closed throttle and should be advanced more. This is sometimes tuned out with a vacuum advance.


My 123Ignition build in a 246gt distributor does not have the vacuum port connected to the disti side but I think I can fix that. I put a similar 123Ignition module on my E-Type S3 and the vacuum on the distributor was able to be connected via a nipple on its side.


Assuming the vacuum input will be available to the 123Ignition module, I see that a vacuum nipple seems to be available on the car. It seems to be a nipple adaptor connected to the manifold just below the center Weber. It is plugged with a rubber vacuum cap. See pics.


First question: is this indeed a vacuum connection to the manifold?


If so, I would connect this to the 123Ignition and program an advance when there is high vacuum such as little/no load. This will allow more time for combustion in a lean condition. If you push the throttle more, the manifold vacuum will be reduced and the advance will be reduced/eliminated. Anyway, that’s the idea.


Anybody else tried to enable vacuum advance on a 246GT/GTS? Why didn’t Ferrari not have a vacuum advance function to avoid these issues?


Is messing with the carbs and jets a better way? The car runs great except for this issue so I am concerned about adjusting the carbs and developing unintended consequences.

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Thanks to all of the comments.

I have used the 123Ignition on my 1954 XK120, 1972 E-type S3 V12 and another car I sold, a 1971 S2 E-Type 4.2L V6. All work very well on this ignition. I have looked at the response in all of these cars and believe the unit is solid and precise. If it does not perform well, it may be that the static advance is not known for the car or the vacuum advance function is not understood and programmed incorrectly. For example, after a rebuild of my V12, the car ran poorly until I found out by measuring the TDC on 1A cylinder via a tool & gauge that the mark was 14-degrees off! Car ran great after the static was adjusted correctly. The vacuum advance in a 123Ignition is absolute pressure, meaning 0kPa=vac, 100kPa=Atm & 200kPa=+1Atm boost. This could be confusing.

Anyway, I have also paid attention to timing advance curve, starting at static advance 0-degrees and using 9-degrees from 500RPM, going up to 39-degrees at 5500RPM. This is the purple curve in the following thread:

https://www.ferrarichat.com/forum/threads/optimized-advance-curve-for-the-246gt.291330/

These are form the thread:
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It is from the "1973 US 246GT Owner's Guide". This car is a US model so it should have 40 DCNF/19 carbs but that's one thing I will check.

My 123Ignition curve is:
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The mechanic I am using has significant experience in tuning 246GT cars and has also done full restorations. We noticed the carbs had some larger/incorrect jets and adjustments but we had changed it all back to spec:

0.55mm Idle jet
1.25mm Main Jet (was 1.4mm)
0.5mm Pump jet (was 0.4mm)

All settings are back to the /19 specs, including the vertical float @ 52mm.

I am running 100 octane fuel which I can get here at a particular gas station serving the motorcyclists taking the popular HWY 9 & HWY 35 run to Alice's here in the Bay Area. Maybe this can cause an issue?

I may try the more aggressive green curve as it does have more advance @ lower RPM. The reasoning for this is to aid in the low-end response, pretty close to what I need. Any reason I should not?

To be clear, there is no residual mechanical advance system in the distributor. It is just the 123Ignition module.

123Ignition confirmed that this unit does indeed have a vacuum port but it is not connected. I would have to install a 1/4" or 5/32" vac bulkhead connector on the disti & run the tube internally to the module's nipple.

Perhaps the low hanging fruit here is to try the green curve, then go through another full carb setup/tuning.

The nice thing about the vac advance is that once the line is connected, I can still not use it but it would be interesting to try....

 

Hi Stefan,

Sounds like you did a lot of work. Glad you’re setup works for you. Not sure what the issues you had with the 123Ignition but it’s worked well for me across a few cars.

My interest is to resolve the occasional throttle opening stumble issue, not trying for better performance or efficiency. Sounds like you believe it is the carburetors and I tend to agree. Perhaps focusing to achieve better idle to main transfer would solve the root cause. Vacuum advancing would be more like a bandaid to the real issue if it worked at all.

 

I’ve tried MSD on a 427 Cobra replica I had for a while and I was very happy with it. The install was in the mid 90’s. I now feel that this is fairly old tech and that’s why I started looking at other ignition solutions.

I like the 123Ignition because of the Bluetooth programmability. I’ve dabble in the ignition systems a bit as well. I also published my work to integrate a 123Ignition in my V12 S3 E-Type in this link:

https://forums.jag-lovers.com/t/installing-a-bluetooth-enabled-123ignition-distributor-on-a-xke-s3-v12/413476

Stefan, I feel that maybe the 123Ignition issues is you’re using the module to directly drive the coil.

That may work with most cars but the Dino is different. It’s a high revving engine and it is likely that the module cannot keep up and can overheat. The distributor holding the module may also be in a pretty hot area and with this added load to drive the coil, this could explain your issues with the 123Ignition system for the Dino.

What I did was use the « 123 Big Fat Spark » (#8755 option) where an ignition amplifier is used to drive a coil with specs selected for this amplifier (#8757 option). This is apparently good to 8000rpm+ for a 6. This is a strong spark all the way to high RPM and the module is not required to drive large currents.

https://www.123ignition.de/123-ignition-en/ignition-booster-big-fat-spark.aspx

I installed the module on the ignition plate that goes in the trunk. I installed it with a good heat sink layer (you could kind of see it as a pale blue layer surrounding the module) that will use the whole plate as a heat sink. I don’t think I need this but I did it to be sure it would stay cool no matter what. The picture shows the coil & drive module. Having low impedance wiring is also key here. Thin or badly connected wires can source ignition issues.

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The top of the distributor with the 123Ignition module. Note the yellow paint mark. That's the 0 degree advance position of the rotor compared to Cyl 3. It is close to the edge since I start at least 6 but I currently use 9 degree BTDC as the min. I want the whole rotor width to be usable for advance timing. At the 39-degree max. advance, the yellow mark would be closer to the other rotor width edge.

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I hope this helps understand my setup better.

As a side note, the mid-range stumble occurred before this upgrade as well. I was hoping the electronic ignition would resolve most or all of the issue but it didn't do much.

I think it is the carburation and jet crossover.

I will continue to research what this is, but I'll look at the jet link if I can find it.

 

Sounds like you put in your time in this area as well.

I see you had issues despite having a similar setup using a separate ignition drive module. I’ll take that to heart and keep an eye on it.

I’ll also take the original distributor and rebuild it as a ready substitute with associated parts (coil, drive module, etc. just in case…