More 123 Dizzy Questions

Just for comparison, I run a 123 dizzy without vacuum advance, set on position “2” and highway acceleration is good without misfire or power loss. Newer Bosch coil, and new plug wires as suggested on this forum. Running dual Stroms with Crespin mod.

May I ask why you chose not to run with vacuum advance? I also have a 123 with the vacuum advance disconnected but was contemplating on hooking it up. Any downsides?

Hi Cedric…the 16 program 123 installation sheet reccomends resistor core silicone leads… it says “Do not use solid core wire, these send out quite a lot of electromagnetic noise thst may interfere with electronic devises” the 123 is an electronic device… change your leads …As mentioned above the 123 supplied rotor is 5k ohm…as this is not a new problem i would reccoment re crinping/soldering the spade connectiond to the coil…Steve

I regard plug wires/leads, plug caps, distributor caps and rotor arms as consumables items. They have a designed life, and regardless of whether they have failed already or not, they get replaced. Dizzie cap and rotor arm, 20k miles. Leads/wires including the caps 30k miles.

I also regularly replace the fuel filter as a service item.

Spark plugs? They stay in the head untouched for 20k miles. But then I fit iridium plugs, which are good for up to 100k miles in modern cleaner running engines.

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since I don’t have strombergs this response maybe irrelevant but… On my '69 triple SU series 2 I’ve had this exact same problem 3 times and each time the cause was water in the dashpots!

Cedric, The car never had vacuum advance so I just haven’t added it. The 123 does have a vacuum option if I change my mind. I also question why an electronic system would need a vacuum. It seems like an odd mix of new and old technology to address a single issue–timing.

The wires I have are copper strands, not solid copper. I believe the solid copper are the ones to stay away from. The problem with pre-made wires is you can’t thread them through the conduit which is original and a look I have always liked. That is why I asked if the Champion Bow Tie terminals could be used with modern wire.

Simply stated, a vacuum advance further adjusts the timing according to engine load. This makes it more streetable, quicker throttle response, and cooler operation.

Pertronix now has resistor core wires in 7mm, to maintain original appearence. They fit in the wire loom just fine.

Multi strand copper has the same issue as solid core.

There is nothing “old technology” about using manifold vacuum as an input to determine the optimal level of advance for the engine under prevailing speed/load. All modern electronic ignition systems do so, as manifold vacuum is a good measurement metric for engine load. The “new technology” of the 123 replaces the crude mechanical methods the original Lucas distributor used to map the engine speed and manifold vacuum into the level of ignition advance required. It replaces springs and cams, and diaphragms and push rods with electronic speed and pressure sensors coupled with modern electronics. This provides greater precision in the ignition timing and improved reliability. That said, if you want to use the vacuum input of the 123 you need to find a source of Ported Manifold Vacuum to connect it to, and the only benefit you will get is slightly reduced fuel consumption under low throttle/engine load conditions.

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Stranded v solid, same problem. You have copper wires. You can use inductively suppressed wiring if you don’t want to use resistance wire.

Having myself had the experience of stubbornly clinging to the Champion connectors, my suggestion is to find the cheapest suppression wires you can find at Rockauto or E-Bay. Leave the current wiring in the holder and install your test wires, just laying them across the valve cover, and don’t forget the coil center lead. Go for a drive. if the cheap wire set fixes the problem, ditch the champions and antique copper and get a decent wire set. Magnecor 67278 will fit in your cardboard holder, and will look right, except without the dreaded champion ends. Or you can spend the summer talking about it and being unhappy with performance.

As for the coil, if you didn’t have a ballast resistor to begin with, your coil should have a 3 ohm primary. Adding a ballast resistor would be unnecessary in that case. IIRC, 123 is good down to 1 ohm primary resistance. Someone with an instruction sheet should be able to verify.

The reason that you might want vacuum is that vacuum is a load signal, which gives you information that can’t be gleaned from RPM alone. Vacuum advance ONLY works in light load conditions, to improve fuel economy and emissions.


Vacuum advance is not a backwards tech, its forward.

Your daily driver with an ECM has a MAP sensor providing the load information to the computer.

Vacuum advance is strictly a fuel economy device and operates only when there is a partial vacuum in the intake system. The reason why it works, again relates to flame fronts in the combustion chamber. In a partial vacuum the a/f mixture is harder to ignite (nothing to do with the advance) but once lit is slower than it would be in full air pressure. Hence for full combustion ie: ideal fuel economy, it needs to be ignited earlier than it would be by the weight driven advance at that RPM. To be clear mechanical advance at high throttle openings (minimum vacuum) deals with normal speed flame fronts but less time to spread as RPM rises.

I had Lumenition 30 years ago, was ok for 7 years
Then I went Petronix 2x
I finally went back to points and have not looked back.
Maybe I am the exception?
Won’t try electronic again unless the points system fails me. I don’t mind resetting them every 2 years if needed

My Jag did not have the vacuum advance when I bought it, so I decided to try a 123 dizzy without a vacuum port.

Why then did Jaguar remove the vacuum advance as part of its emissions strategy? My 50+ year recollection is that mechanical was considered more precise, whereas the vacuum was variable and less controllable. But I am not an engineer, I was only told that by someone who was.

Am not representing this article as definitive, but found it interesting.

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The article is correct. A race car is under load all the time, and does not excede 36*.

A street car idles in traffic, and cruises at 60 mph.

The vacuum advance corrects the timing for these leaner conditions to maintain the peak cylinder pressure at the correct crank position.

However, this increases hydrocarbon emmisions, so GM and the STP NOX device used ported vacuum to increase combustion temps at idle to reduce emissions.

Increasing the advance at idle runs cooler.

When power is required, the vacuum drops out.

The only time you want further advance at cruise is under light load, therefore the mech advance needs to top out at 36*, and use vacuum advance only to excede that figure. A mech curve exceding 36* without vacuum advance is not what you want to do.

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I just checked my distributor and cleaned ,oiled and checked the gap on the points. I checked my
boot and have extra points ,rotor, etc. All is fine and working properly what justification do I have for switching to 123 which will cost almost $1,000.00.

None if the curve is correct. Kettering ignition works fine when correct.

No. Precision has nothing to do with this. Centrifugal advance responds to RPM only, vacuum to load. Both of them are miserably imprecise when compared to electronic systems.

What you have to realize is that prior to catalytic converters, emissions systems were lipstick on a pig. Among the tricks used were retarding ignition timing and leaning the mixture to raise exhaust gas temperatures, which lowers tailpipe emissions of unburned HC’s. This is what prompted the change.


Interesting article. Thanks for posting it.