Rats nest tutorial wrong on vacuum advance?
 

The tutorial says to use the second nipple from the left for the vacuum advance, but this nipple *never* has any vacuum. So the vacuum advance doesn't work at all.

Based on a little reading, I'd expect the vacuum advance nipple to activate only when on throttle. This behavior is seen *only* on the [edit: fourth] nipple from the left [next to the mixture screw], which the tutorial says needs to be connected to the ventilation. So, which is it?

I'm not sure if the vacuum advance works properly when connected to this nipple, but I know that it _doesn't_ when connected to the second from the left. If I still want to use the purge valve, how should I connect it?

Okay, here's what I'm going to do. I'm going to run a short vacuum tube from that nipple to a T, then I'll connect one end to the purge valve and the other to the vacuum advance. Good idea?

Hmm, I have a few numbers and a question.

At idle, the vacuum from the #1 nipple (for the A/C relay) was about 18 units at idle and I eyeballed about a 5-7 degree vacuum advance when connected to this at idle.

At a little over idle (I can't actually see the tach, I'm just tugging on the throttle cable) the 4th nipple seems to produce about 5-6 units worth and about 15 units of vacuum when tugged harder (max).

So, then, does the vacuum advance only account for 5-7 degrees timing advance max? What should it? Or, is it proportional to engine RPM?

Can someone please verify that this isn't just me? You don't even really need a vacuum gauge (although it would be nice).

Check to see if you get any vacuum at the second nipple at idle or when on throttle.

when i ran vaccum advance (don't anymore and it works beautimusly) i T'd together the two and then ran them in to one all the way to the vaccum port. worked just fine.

Thanks but that's not what I'm talking about. Obviously the trailing and leading are t'd together as per the tutorial, but the 2nd nipple from the left doesn't have any vacuum, ever.

they are t'd together? i didn't know that. thought the trailing and leading had their own hose off the intake.

They don't connect two separate nipples. just cap them off at the carb and at the dizzy leave them open. Set the timing at 4k rpm

Carl's out racing for the weekend, and I haven't seen Pratch in a few days.

Wait until monday or tuesday, you'll get the best response out of them. Wait 'till monday and bump this thread up (bookmark it for now so you don't forget). It would definitely be interesting to know this.

Jon

Yes, it would be interesting. What I really want to know is if this is a problem specific to my car or if the tutorial is incorrect.

All someone has to do to test this is to disconnect the second nipple from the left and see if it has any vacuum under light throttle. You don't even need a vacuum gauge; you can just feel it with your finger.

i'm on it... *runs outside*

i never ever thought about seeing if there was vacuum off of that nipple.. but I too don't see any vacuum coming from that nipple (feel if ya wanna get technical =D), at idle or with some throttle...

i also tried that pcv off of a caravan deal because i broke 2 purge valves.. hooked it to the air cleaner but still got the condensation under the oil cap.. so maybe it's time for a refresh of the nest's removal? :)

Well, I can't say about broken purge valves, but from reading the factory manual I can say that, like the vacuum advance, it _does_ require a source that has vacuum on throttle but not on idle. This apparently is to keep it from affecting your idle.

The fourth nipple gets progressively more vacuum with throttle. This is how I'd expect the vacuum advance nipple to work.

So, my solution is to use a T fitting from that fourth nipple, running one to the vacuum advance and one to the purge valve. It seems to work fine.

Hmmmmmmmm. Well all I can say is that Im fairly sure that I followed the original routing of the vacuum for the advance as it was with the rats nest on. However I may have made a mistake. The vacuum advance should be on port vacuum, not manifold vacuum, so your right on that point. All I can suggest is that someone trace it out from the diagram. *Cough* Jon *cough*. It is also possible that I got the routing right (we shall see) and that the solenoids played some part in controlling the flow of vacuum to the dizzy at idle, although as I best as I can recall, they dont.

The vacuum advance does only account for part of the total ign advance, the mechanical part kicks in later and advances it even more.

Stupid question here. If the mechanical advance is there and advances farther than the vacuum advance, why should I worry whether the vac advance is working at all?

Because the mechanical advance doesnt come into play till later in the RPM's. Keeping it all working right will add to your gas milage and street driveability.

OK. I better go check on whether I have them hooked up to a vac source. I'm pretty sure I did when I first removed the rats nest. But as I've continued to fix things til they break I may have changed things.

Rutnick
 

look at the diagram under the hood. The only thing I used the tutorial for was the size and amount of the hose to use. If not under the hood, try the Haynes manual.

I removed my rat's nest about 2 weeks ago. The sun came out. The birds sang. I didn't have anymore lung mustard. I lost 10lbs!

Leading and trailing used to have differing amounts of vacuum advance. The FB had the same amount. It remained backwards compatible.

I don't even use vacuum advance.

Re: Rutnick
 

I posted that one. For some reason, I was logged in wrong.

Alright,

So I need to switch my vac. adv. to the 4th nipple?

Then what about the vent. hose, which nipple for that?

Also, anyone else having problems with their cruise not working with the rat's nest removal? I've got no cruise and not sure how to begin looking for the problem.....(Yes, the switch is on)

Re: Rutnick
 

what's your secret? i only lost 5 lbs. :D

1stgen_tn: You can use a T-fitting to connect both the ventilation and the vacuum advance to that nipple. BUT, I think that Carl is right; it should have been that second nipple. I can see two ways of testing this:

1) Someone with a functional rats nest connect a vacuum gauge to the hose that connects to the leading vacuum timing advance and let us know what the vacuum there is at 1000, 1500, 2000, 2500, and 3000 rpm, and we can compare it to that fourth nipple; or:

2) Someone reconnect the vacuum soleniods and see if they have some affect on how the second nipple from the left works.

Re: Re: Rutnick
 

more driving, less eating....

Well I'd figure all the nipples sucked some kind of air anyway. I mean, aren't most of them coming from the holes in the black spacer (whatever you call it) between the carb and intake?

...Or are they all different b/c somehow they are routed specially throught the carb?

What about the mikuni/weber setups? Is there even a place for vacuum advance hoses to run to?

I like the idea of timing @ 4k rpm myself, that is, IF the car still idles somewhat reasonable.

Someone take Bouis' suggestion and test for us.

1stgen_tn- yes it makes a difference. Different routing exactly. Some see manifold vacuum all the time and some only part of the time.