Can you run the 123 Dist with the vacumn port blocked off?

I made the mistake of ordering the 123 Dist w the vacumn feature. I don’t want to use vacuum.

Does anyone know if I can I just plug it off and run with full programming of the advance?

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Can you return it ?..

I’d rather not if can just run it w/o vacumn

Just curious - why wouldn’t you take this opportunity to add a vacuum advance? Seems like if you do much highway cruising a vacuum advance and the flexibility of programming the 123 to allow for it would be advantageous.

But I will admit I know nothing about the 123 - still driving in the stone age here.

If you have the Bluetooth version I would imagine you can just blank it off, and specify a vacuum map curve where zero advance is used for all pressure levels. That is what I did with mine until I connected a vacuum source.

David - Did you see some advantage to having a vacumn advance? Most 123s on other cars just run straight programmed advance.

When Advanced Distributors rebuilt my stock distributor, he removed the vacuum advance entirely. Said it was worthless and made primarily for emissions and would not help performance.

You can blank it off if you want to keep dust and water out of the little hole. I did precisely nothing with mine. It works fine.

Thanks… That’s what I was hoping.

The vacuum advance should give you some benefit in reduced fuel consumption when cruising at moderate speed. It will not improve performance. I connected it up on my 1969 Series 2 (which had no vacuum unit on the Lucas distributor). I haven’t noticed a significant improvement in fuel consumption, but I haven’t experimented with the vacuu advance curve much either.

That’s very odd…I’ve “known” Jeff Schlemmer for many years, he’s done at least 8-10 distributors for me, and he typically swears by the benefits of vacuum advance in all but the most specific cases. Are you sure you didn’t have some goofy distributor from the “smog age”, with vacuum retard?

Vacuum advance has nothing to do with emissions. Apart from the added efficiency at cruise, it also remains in play in any part-throttle condition, so I find my cars are much more responsive around town with it connected.

Your engine can also run hotter without the vacuum advance.

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Yes you can run it, but if you leave the vacuum port disconnected, then all that will happen is that the unit will measure the pressure and think it is 100kPa all of the time (assuming you are not at altitude). This means the ignition advance you’ll get will be that as if the throttle is wide open all of the time and you’ll get none of the benefits increasing the ignition advance when the engine is at partial throttle, i.e. 99% of the time.

Pretty dumb thing to do imho. Just connect it up to the main inlet manifold like any sensible person would.

Plugging it is subtly different from leaving it disconnected. When you leave it disconnected, it measures atmospheric pressure and returns the advance associated with that, i.e. always ambient air pressure and no vacuum. If you plug the line, you trap and lock in the setting based on how much air is in the stub - it will be floored at atmospheric pressure but may be higher if you have compressed what little air is in the plugged tube. On balance, that ought not affect what you get unless the unit was destined for a turbocharged car, in which case it’d have settings for pressures higher than atmospheric pressure.

kind regards

You probably had a vacuum retard distributor, not a vacuum advance distributor. You would need to install a ported vacuum feed to use vacuum advance. Installed correctly, vacuum advance will reduce fuel consumption.

Thank you. That is exactly my understanding of how my S1 works and why the vacuum line is ported where it is on the carb…for vacuum retard

I thought vacuum retard was introduced in 1969 to meet emission requirements.

Normally, but the 123 allows you to program the vacumn advance curve for any pressure so ostensibly you could program a “0” value for all pressure.

Yes, that’s what I had (late 70 S2). Vacumn retard. That was what Advanced Dist removed.
I’m running triple SU’s with the vacumn port on the front carb. I’m assuming that’s the vacumn port I would use if I wanted to?

There must be an echo in here.

So, why are you using that as your “go by” for not wanting to run vacuum advance? They are apples and oranges.

There is literally no downside to vacuum advance, and numerous advantages.


Are you saying your SI has vacuum retard ?

Not from the factory it didn’t, an nobody with the most basic understanding of engine operation would have fitted one.

No. The S1’s had ported vacuum for vacuum advance. The later S2’s had vacuum retard, with direct manifold vacuum.