I got one of my boys a 123 Distributor for his '74 2.0 with stock FI. I've had one in my 912 for some time and love it. We pulled the motor last year, just got it back together over the last 6 weeks or so and had some trouble sorting it. The two big changes while the motor was out were a rebuilt throttle body and the 123.

When we got it running, there was a big surge at 2800-3000 and the plugs looked rich. We fooled around with resetting the TPS, and a few other things and nothing seemed to work.

The original curve was the one from 123 that included vacuum advance on the bottom part of the curve. I spoke to 123 at one point and they told me vacuum would let it return to idle better, but it always kind of bothered me to have a state of the art digital device relying on vacuum.

Last night we scrapped that curve and went with a totally digital one. Problem solved! Blast right through that range with no problems. I don't know what was happening with the curve when we were trying vacuum advance, but frankly I don't care enough to spend any more time on it.

Try this if you're having any issues-curve attached.

Click to view attachment

Rob

Sure you had it connected to ported vaccum?

Not sure if 74's had it on the TB.

Yes, this 74 has a vacuum port on the TB. It just wasn’t working and I’m happy to get rid of one more vacuum device.

That is a retard port on the 74. They didn't have advance.

This is what I thought. So two types of vaccum signal....ported and manifold and they work differently. If you had hooked up manifold vaccum to the advance port on the dizzy it would do as you described.


Post a pic of the TB.


Modern cars still use vaccum signals for lots of things and if the chip shortage last much longer they may go back to mechanical signals....lol.

I'm done. I like having total control over the advance curve digitally. Not going back to hunting for a working vacuum port. I just don't see a reason for it.

But you guys have certainly brought up one reason it might not work for others!

So part of the reason for having the vaccum advance still is that it is a feedback loop albeit vaccum sourced...non digital form to provide a part load feedback not just based on RPM's of the engine.

On part load when the mixture tends to be lean and the mixture takes more time to burn the part load advance (ported vaccum) on the throttle body provides this.

But this post would be for others since you are done learning.

Well, advance by vacuum wouldn't be an option on this engine anyway. However, there is a setting in the 123 for using the retard to stabilize the idle. No clue if it is worth it. I have been eyeing them and was surprised to see you could add that.

Hey Rob.

Quick question: how did you arrive at the multi-point curve for your 123? Was it step by step, trial and error, until it worked best?

I have one set straight-line from 1000-3500 RPM that works great but would really like to optimize it. I have not dug in yet because I am not sure how to approach it.

Thanks.

@Robson51 question for you, is this D-jet yes? is your 123 distributor a bluetooth enabled or the switch select option for pre-set curves? if so, which curve did you select? if you are not jsing the vac(which as the guys said is a retard port and would slow your idle) then the 1-6 options are for you. i currently have been hooked up to the “B” or ”D” since i am using the vac and A-x are for if you use that. i found my idle to be too high without it but the preset curve very flat, and wish i had the ability to adjust that more to the way it works with a factory vac retard and mechanical advance.
anyway i am always curious to hear how others are using their 123 ans how it works for you them ans what setting they are using , so thanks for the feedback .

Phil

Yes, it's bluetooth and D Jet. I first bought one for my 912 with Webers and then got this one for my son's car. The curve I shared is the vacuum advance+the recommended advance. It works perfectly so far. No issues with idle or driveability.

This curve was just a simple adaptation of one I found. It is similar to my 912 curve, but a bit steeper in the beginning and with less total advance. I don't have access to a dyno-all the ones around here only want to fool with big horsepower-and driveability was the goal.
We've been playing with this for a long time through FI issues, rust, etc, and it's time to just drive it.

I'm sure most everyone has read this:

If not here it is.



https://members.rennlist.com/pbanders/distributor.htm