123 R-V-IE Distributor vacuum question, Stock D-Jet 1.7L in '72 914-4 Options

[Stev914]

Greetings 914 Worlders:

I'm happy to be asking this question when my car is running GREAT. I'm just really trying to understand how the engine works, and I am puzzled by this.

Q. How does the 123 R-V-IE work with one vacuum line when the stock distributor has two (advance & retard)?

Longer story:

My local mechanic recently replaced my stock distributor with the 123 R-V-IE and adjusted the settings. The engine is mostly stock and has the original D-Jet. It's driving great. I note that there is a single vacuum line into the distributor (I assume this is vacuum advance). The other green hose (I'm assuming this is the retard) is fitted with a plug. Car runs great.

I have my old distributor, which has the advance and retard connections, exactly like you see in this video tour by George Hussey:

https://youtu.be/ioJ1yYU5MrM?si=sEvnLv0Z_cDd_h1s&t=220

Again, the vacuum retard hose in my car is just fitted with a plug now. I am assuming that's not a problem, but I am still wondering how the 123 R-V-IE is meant to integrate into the vacuum system. Here's a great illustration I found here on this forum posted by Jeff Bowlsby:



Sorry for the very newbie question.

Steve
1972 914-4

[worn]

I defer to others but I think that the modern dizzy can use one signal to handle both advance and retard, while the original used two different types of vacuum signals to accomplish the same function without bits and zeros and ones.

[emerygt350]

I am not sure about Bluetooth versions, mine is the non-bluetooth, but I have found you should only run it with advance off ported vacuum (port on the tb pointing towards the front of the car) and not with retard (port facing the rear of the car). You can only choose retard or advance with the 123, not both.

The original design was very clever and would do interesting things as the two vacuum sources worked against each other in part throttle situations, which is almost all of your cruising. In the 123 I found the retard was very much just on or off and often at the wrong times.

So... If it's hooked up correctly and just giving you advance I would leave it. If it is hooked up to the retard port on the tb, I would think about plugging it. I am sure someone will chime in with how the Bluetooth uses the signal, if it's any different from the non Bluetooth version.

[Stev914]

Thank you for those explanations. It's helpful.

The big picture for me is that, while I am semi-handy, I don't know much about engines. I'm still building a mental model of how this thing works.

As I understand it, the R-V-IE model of the 123 dizzy (look at me using new lingo) is the non-Bluetooth version that has both vacuum advance and D-Jet compatibility. The advance curve is set manually by a switch on the distributor itself, as opposed to connecting by USB or Bluetooth (which is just fine by me--my goal here is "set it and forget it").

I'm going to take the winter months to read and theoretically understand how the entire engine works. This site and YouTube are great resources. But asking questions always leads to more questions for me.

Q. Is there a good repair manual or book that breaks down the Type IV 1.7L D-Jet engine well? I'd love some recommendations.

Q. Is there any negative impact of the "retard" hose not being hooked up to the distributor (apart from the distributor not getting retard)? In other words, is this a "break" in the system that denies some other component vacuum retard, or it it just a function of vacuum retard not going somewhere?

Again, sorry for newbie questions. My goal is to read these posts of mine next year, shake my head, and realize how far I have come in my understanding thanks to you all.

Steve
'72 914-4

[emerygt350]

I actually like the non-bluetooth. Some of the best info is going to be on this forum but the Haynes and clymer manuals are good to have on hand. Neither will give a whole lot on d-jet though. For that you need to hit pbanders https://members.rennlist.com/pbanders/ and the other d-jet forums. That is probably more than you need right now though. The book by Tim Wilson (on Amazon) is essential. That tells you all you need to understand the type 4.

You can unplug the hose without any issue. Just make sure the port/s on the throttle body are capped. Some have both the retard and advance others only the retard. Just depends on the year. I put a cap on my 123 vacuum port to keep it clean.

You need to verify which ports you have on your tb and you need to verify which program your 123 is using. Then you can know whether you should hook it up or not. I am not too familiar with the 1.7 TB. The front and rear ports I mentioned are specific to the 2.0 TB. The 1.7 was stopped for the 74 year so it might have always had both ports.