yayarx7

unhook the two vaccuum lines going to the dizzy

SilverRocket

Right. The vacuum advance only works when there's vacuum (imagine that ), or in other words when the throttles are closed. It is more or less an emissions feature, to help the cats do their job at idle. Since most of us don't have cats, we don't need it You'll notice your idle become smoother and your emissions get worse when you disconnect it. It also makes setting the timing slightly less confusing.

There are two vacuum diaphrams on the distributor with lines going to the rats nest. Remove the lines and cap the inlets at the rats nest / base of the carb. (My memory is a little foggy here because I removed the whole nest and everything a while back). Do NOT cap the inlets on the dizzy diaphrams, leave them open.

It's not a locked ignition system. The vacuum advance has no effect at WOT anyways, the mechanical advance inside the dizzy advances timing approx. 20 degrees from idle to 4000 rpm. If you want to lock your ignition system you need to modify the dizzy, but I'd leave this to the hardcore roadracers.

No problem dude, the old timers on here can probably remember me plaguing them with questions about all this a while back!

V8kilr

ok so the rats nest is located under the carb?
i always wondered about that.
plug the lines that go under the carb
and leave the ones that go to the dizzy open
there are two lines?

do i have all this correct?

paul yaw says your idle will be rougher if you do this,
you say smoother?

but i have a full aftermarket ignition system minus dizzy so im not worried.

SilverRocket

This is how it was for me and at least one other person I know. Vacuum advance sucks lol.

Nope, the rats nest is the mess of vacuum lines and colored plastic solenoids which is located right on top of the engine.

Yep, there are two diaphrams, two lines, and two vacuum control solenoids on the rats nest. One is for the leading, the other is for the trailing.

Like I said I don't remember that well... whatever you do just leave the inlets on the dizzy diaphrams open. Then just cap off wherever the lines went, I can't remember if that's at the base of carb or just at the rat's nest. Sorry I can't do better than that.

(my car's in storage right now and I don't have all my stuff here with me at school, I'm just working from memory)

V8kilr

ok if its nice tommorow i'll do that,adjust my timming,
and maybe convert my ignition over to direct fire since i have all the components to do so.

if i do all i will posts all my results to let everone know how it goes and if there is a noticable diference.

will also buy new dizzy cap and rotor.

SilverRocket

If you're interested in reading more people's results and opinions, look into the old posts on this forum and also www.mazspeed.com . Lots of people have experimented a lot with this stuff, it definitely isn't new ground. Same thing for if you're interested in different ignition setups/direct fire, the info is all out there.

peejay

The vacuum advance isn't hooked up to manifold vacuum, it's hooked up to PORTED vacuum. (pretty sure of that anyway) There should be no vacuum at idle, then when you crack open the throttle blades the port sees vacuum and you get vacuum advance based on manifold vacuum. (basically it's like manifold vacuum except the port doesn't see vacuum at idle)

At least, that's the way my '80 was. Haven't played with timing lights on the '85 yet.

SilverRocket

Peejay,

That's contrary to how I've always seen it described before. I believe I'm correct in my initial description, based on previous (drawn out lol) forum discussions all about this, and Yaw's website.

From Paul Yaw's website:

"When the throttle plates are closed, or just partially open, there is high vacuum in the manifold. The reason is that the engine, which is simply a pump, is spinning away trying to draw in air, but since the throttle is blocking airflow, a great deal of suction or vacuum is present in the manifold."

This vacuum, actuated through the vacuum advance pot will advance the timing based on the intensity of the vacuum. As you open the throttle, the vacuum lessens, and the timing advance decreases. At full throttle (Butterflies all the way open.) the vacuum advance has no effect on the timing, because there is no manifold vacuum. "

Also, a forum member I happen to be friends with (RXcetera) has a switch on his car that turns vacuum advance on and off. You can clearly notice the difference in the idle when this happens, so it must obviously be doing something at idle. That means it functions on manifold vacuum as far as I know.

That's how I understand it anyways.

peejay

Hmm. That's not how my '80 was. Interesting...

SilverRocket

Interesting for me too, I didn't know what ported vacuum was before you posted that

It is possible your 80' was special in some way, ie. Cali car or something like that? I wonder why it would be set up differently from the later models

peejay

'80s were just goofy-assed

Maybe one of the solenoids disabled vacuum at idle speed? I never paid much attention to how the emissions controls worked

SilverRocket

And that's the way it should be

They don't work quite as well when they're in your basement gathering dust

peejay

Actually they're still on the engine gathering dust. Just yank it all out and stuff in a different engine...

FJ

Just to clarify: the mechanical advance is 12.5* (13.75* for -SE) and is fully advanced at 2000 rpm, at least for '84, '85 models. Maybe it was 20* for earlier engines and that is what Yaw is referring to?
Contrary to how it sounds from reading Yaw's page, a stock system will cut the vacuum at idle, using the solenoids. That is why they don't mention disconnecting the vacuum lines to set the timing in the manual. The -SE single solenoid and the 12A Leading open at about 1000 rpm. The 12A trailing opens at 3000 rpm. (The mechanical is fully advanced by then at 12.5*, but the trailing vacuum advance is higher at 15*.)
As mentioned, there is no vacuum at wot so the vacuum advance is used only for partial throttle, not at idle. When you are at high rpm and let off the gas, the vacuum will jump. As you do not want advance in that case, the solenoids also cut the vacuum then.

This got me thinking, so I checked my manual (factory '84).
For the 12A automatic and the -SE, that's the way it is: the vacuum is tapped before the primary throttle valve and the 12A manual is after the throttle valve. So your '80 wasn't so goofy-assed. As the solenoids cut vacuum at idle in either case, I don't see it making much difference where they are tapped in, maybe slightly higher vacuum for small throttle openings if tapped after the throttle valve . Without the solenoid, it would work as you said for the -SE and the auto, but not the 12A manual. Why the difference?

I don't know why RXcetera would see a difference at idle, if everything is stock, unless his solenoid is shot.

SilverRocket: I thought Racing Beat recommended 7.5*, not one. I didn't find it on their site, did you have a link?


-John.

SilverRocket

Hmmmm.... I've never heard that before! Interesting...I know for a fact that isn't how my 1982 distributor works. Mine advances approx 20* by 4k rpm with the vac advance eliminated, I'm absolutely sure of it. I don't have a clue about any other years though...

Well I don't want to put words into his mouth, I distinctly remember witnessing this but it's possible I'm wrong... he's not running the Nikki anymore but I'll ask him about it next time I can.

It's not on any website, it's in their manual/catalog. I don't have it personally and it's been a while since I did this stuff, but now that I think more about it the numbers 2L and 19T at idle seem to stand out in my head. Personally though, it's pretty hard to be precise to a degree when setting your dizzy. I just remember setting mine a degree or so over stock. It's definitely not 7.5 as far as I can remember though, that's a hell of a lot of advance! They do have lots of different recommendations for different setups though, you might be thinking of a different one than I am.

Hold on though, wouldn't that mean what I said makes sense for the 84 12A manual then?

It seems to me like there may be a few big differences between years in terms of this stuff, since none of our cars seems to work the same way

V8kilr

i have the rb manual and couldnt find to much useful info on this in there.
anyway i got an even bigger question on this direct fire that i cant seem to find,and as far as i know no one has asked.
will posts new thread for it because it is very important for me to know before converting,or anyone else to convert for that maner.
oh btw ill check to see how much and where the spark advances when i do my timming.

FJ

Sorry, I didn't mean to imply that you were wrong : At the beginning I said "At least for '84,'85 models". I was clarifying that the 20*,4k rpm numbers were not the case for the '84, '85 engines, according to the manual. As I mentioned, it may have been different for previous years.
Looking at Yaws page: I don't get it. If it is 20* for the earlier models, like yours, fine. But he mentions the 13b so he must be referring to '84 also. Either he or the factory manual must be wrong. Mine is in storage or I would fire it up and play a bit.
On the other hand, I found a jpeg of the Racing Beat chart on the Mazdatrix site. The 7.5 I referred to is for the -SE only. I circled it, in the top right. (You'll note your memory for your car was correct. The advance increase is not as high for the 12A with RB or Yaw.) The factory setting is 5ATDC for leading, so -5 + 7.5 = 2.5* BTDC for RB at idle. Add the 13.75 mech. advance and you get 16.25* total advance at 4k rpm.
If we use Yaw's 20* advance, the RB total advance would be 22.5, almost as high as Yaws 26* BTDC total for the -SE. As the RB numbers are supposed to be much more conservative and safe than Yaw, it makes more sense to me if the advance is 13.75*, not 20. The 12A settings by Yaw are not as far from stock as the -SE, but the 20* or 12.5* question remains.

I don't know if the book is wrong or I'm missing something, but once my -SE comes out of storage, I'll definitely be checking it. I would like to know the bottom line for the '84 12A's also, if someone wants to put a timing light on theirs. When the search function comes back, I'll have to see if there is an answer there.
My original reply was intended to clarify the advance values for '84, '85: Looks like that's turned to pupshit. Now I'm "dizzy."

Quote:

Well I don't want to put words into his mouth, I distinctly remember witnessing this but it's possible I'm wrong.

Again, I don't intend to say that his couldn't be doing that, just that if it's '84 or '85 it shouldn't, according to the manual.

Quote:

Hold on though, wouldn't that mean what I said makes sense for the 84 12A manual then?

I'm not sure what you mean: If you are referring to where you mentioned that the vacuum operated the advance at idle, then only if you bypass the solenoids. The solenoids block the vacuum at idle.

Quote:

It seems to me like there may be a few big differences between years in terms of this stuff, since none of our cars seems to work the same way

Agreed

-John.

V8kilr

hey look its a racing beat manual,
too bad i got a 12a

stock
stock
stock
stock


yep thats all i get to read.