My newest question got lost in an old thread, so I figured I would try a fresh one....

My 75 L-jet has the below vacuum line layout. No EGR, Decel, or Charcoal can. To help an erratic idle, it was suggested that I check operation of the advance plate in the disty, via the vacuum can. So I pulled the yellow line off of the TB and put a vacuum on the line. The plate in the disty shifted and sprung back when the vacuum was removed. Seemed correct.

I pulled the purple line from the TB and again put a vacuum on it. But got no movement. It felt as if I was sucking on an open hose. I pulled the hose, plugged the end and felt vacuum. So the hose is good.

I suppose this is a problem.... but is it my problem with idle. What does the vacuum on the disty side do?

Click to view attachment

The vacuum retard diaphragm leaks.
So you have a vacuum leak and your timing is not being retarded at idle as it should be.

You can replace the vacuum canister, if you can find a good one.

You might be able to plug the hose to stop the vacuum leak and then reset your timing and idle and see how well the car runs.
The retard is primarily for emissions.

Jim

your car does not have a yellow vacuum advance only the purple retard, which sucks the timing down for a better idle. Since it does not work you idle will stick high but once you drive the car will operate correctly. At rest check the mechanical advance by twisting the rotor and make sure that it springs completely back

I don't follow. I have both yellow and purple hoses. Both are attached as in the drawing.

I had thought that for a test, I would remove the purple hose and plug the TB and the disty side of the vacuum can.

Sounds like I should fine tune the timing and idle after that.

Is an advance only can easier to find?

No they are not. At 50 years old most all of them leak.

This is the route that lead me to get the 123 Dizzy.

Good luck finding one that works.

Yeah, I have that on my wish list. 'bout $600, right?

I found a guy on the samba that rebuilds distributors. Guess I will see what he has for parts,etc.... I wonder if a one port can from some other vehicle was work?

Since I removed most of the Emissions stuff, I should just delete the retard function too. Probably has never worked anyway.

Clark, what model distributor is your’s?

Not too sure. I'll have to take a close look this evening. IIRC it came with the car. I am pretty sure I did not change it.

123 Dizzy is $300-ish. Getting your distributor rebuilt will probably cost you a decent chunk of change and may not include the vacuum canister. I just went through this and ended up buying the 123 dizzy.

I'm a little confused here. First, Jake Raby has written that the vacuum retard significantly reduces emissions so I'm a fan of them. I've also read the retard can give a smooth, lower idle but don't know if that is true. That said, if your advance port is holding a vacuum and you are thinking of just dropping the retard, I don't see the problem just using the canister you have. If the diaphragm was leaking, you wouldn't be able to hold a vacuum on either side (advance or retard). Sounds like yours is more likely leaking at the port fitting. I have two that are leaking the same way. You should be able to just plug the vacuum port on the throttle body if you are willing to give up the benefit of the retard. What am I missing?

How in the hell do you know what disty to get? There are lots on the web that LOOK like what I have.

New, used, rebuilt, cheap, expensive, with can, without the can, can with 1 pipe, can with 2 pipes

Even found an eBay dude selling cans.... $80 NOS, still in the box.

Even saw some posts suggesting no can needed or centrifugal adv is better. Guess that is why AA sells a no can disty.

So here is my thought. between 1500 and 2500 rpm the can advances the disty plate. Pull to a stop sign and the throttle plate closes and puts vac on the retard side and helps the spring close the disty plate.

Each car pulls different vacuum, so that is why the cans and springs may vary?

You are probably pretty close to correct.
The system was designed around having a functioning vacuum retard.
So the time curve is probably different overall.
The system may not idle as low as it is suppose to without retarding the timing at idle.
With the time manually set retarded at idle to compensate for the failed retard canister, you may not be able to get the proper advance.

From what I recall, the canister has 2 diaphragms, one for the advance and one o for the retard. One is leaking and the other should work normally.
The canister has springs in it and should always return to the same starting point regardless on whether it was advanced or retarded by vacuum.

NOTE: The vacuum advance/retard is separate from the mechanical advance. The 2 types of advance work in a cumulative manner, meaning they add or subtract to/from each other.

I would plug the hose or port at the throttle body and reset my total advance and see how it runs.

Jim


Jim

I am not sure how long or if the retard vacuum has ever worked. So I guess I already gave it up.

If it adds smoothness to the idle, then I would like to see "how" smooth. Would I even notice? I suppose plugging the TB retard port will close a small leak. Probably would not hurt to check the timing, but I would bet plugging a leak would not change the timing, right?

I think there are 2 diaphragms, so one puncture does not ruin both, correct?

Generally the advance side fails leaving the retard side working,I have never heard that they can be rebuilt,far as I remember there is a guide on the net that shows vacuum canister numbers and what they are off,if you buy a replacement that is similar to look at and the number is right you should be good,cheers

Get a 123, tune it, and be done with all this bullshit.

Now I want to see a cutaway of the canister. The two diaphragm design isn't making sense to me because there is only one actuator arm connecting the diaphragm to the advance plate. On diaphragm makes more sense. Suck on it in one direction, you get advance. Suck it in the opposite direction, and the arm moves the other way to provide retard. I'm not sure how dual diaphragms would work with a single actuator.

Here are the specs on the various 914 dizzies from the tech spec booklet. I originally posted them on this thread here. Might help with selecting dizzies.

Not a cut away but a drawing.

It does not show well but #7 and #8 are the 2 separate diaphragms.

Click to view attachment

Here is an old thread .......like me.

http://www.914world.com/bbs2/index.php?sho...p;#entry2414651


There IS an cutaway view somewhere around here if you search. I can't remember were I finally found it but I think it came from Dr. D-jet in Germany or another antiquated Bosch website somewhere.

I know this:

The cutaway will show a dual spring with a single diaphragm. So, if one side leaks...you are screwed. You won't get the right advance or retard.

This is the exact reason I went to the 123. You can just program the thing to the right curve that is specd.

I have absolutely no affiliation with them BTW and they don't post here normally if someone has a dizzy problem.


Edit:

Shiza! Somebody found one. I don't know if that is a Bosch. I don't recall an adjustment nut ever on the D-jet dizzy's. I could be wrong.

Thanks for that! Very interesting. It looks like the function sort of like a single, double-walled diaphragm but looking how they are ported, it looks like if the advance diaphragm fails, you'll lose vacuum on both sides whereas if the retard side fails, you would lose only retard. I'm guessing the purpose of pulling vacuum from between the diaphragms for the retard is to get different lengths of pull on the arm. A lot more going on inside those little cans than I thought!

Fancy one that would work on the L-jet is $509.... $$450 for no tuning model. Wonder why none of the group buy folks have given the product any reviews? Having too much fun driving I guess.

Do a search. There are a few reviews by people. I haven’t heard anything but positive results. I’ve been happy with mine so far. No points, no failing canister, no worn distributor shaft. Hopefully it will last a long time.

mrfiat.com had the cheapest price on them I could find and only $10 shipping.
I couldn’t find the exact model I needed on their website, but an email to customer service got me an email back saying they had them in stock.

Their direct customer service line:
Italian Auto Parts, Inc.
Phone: 678-637-5103

That's because you have dual vacuum pickups on your TB and why you have no decal valve because that helps to stop the single vacuum TB which only has retard pulling back too fast and stalling your engine,to my knowledge that's how it was done,strange shit in those early days emission exercises which used the owners as victims ?.
The retard pulls back early advance to prevent richness created by deceleration...something like that.

I installed Porschef's loaner disty today.

Checked the timing to know where I was before the change.

Set Fan and rotor to #1 using the one wheel up method.

Pulled my disty

Checked the vacuum on the loaner with a hose. Both work.

Cleaned up the loaner

Cleaned the top of my engine a bit. During my last vacuum (smoke test) i saw smoke coming from my disty, so I put a new o-ring on Joe's.

Installed the loaner, set the idle (bounced a bit from 950 to 1050) set the timing

installed the advance and retard hoses, reset the idle, went for a drive.

There are so many variables with this change, I don't know for sure what did it, but at every stop sign the idle dropped down to the 1050 - 950 range. Joe's loaner was a different model bosch. He had a petronix module in his, mine had hot spark, His vacuum worked, mine had a leak.

ALL IS WELL.

Excellent

Now take it out for the aforementioned thrashing and see if you notice anything different (pinging/acceleration/smiling more... )

Then start saving for a 123. It's pricey, but worth it