No vacuum line port off head

AKimball92

AKimball92

True Classic
I feel like I’m making this forum all about me... I’ve got another problem.

The head I’m using 4444407 is a 12 bolt 1500 head but doesn’t have a vacuum port. I am using a vacuum advance Ducellier distributor. Where can I pull the vacuum? Also I purchased the 36 DCNVA carb from Steve. Haven’t really looked at it yet and still fairly ignorant on carbs but it too might need vacuum.
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AKimball92 said:
I feel like I’m making this forum all about me... I’ve got another problem.

The head I’m using 4444407 is a 12 bolt 1500 head but doesn’t have a vacuum port. I am using a vacuum advance Ducellier distributor. Where can I pull the vacuum? Also I purchased the 36 DCNVA carb from Steve. Haven’t really looked at it yet and still fairly ignorant on carbs but it too might need vacuum.
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I capped the vacuum port on my dizzy. I'm not sure if it's an advance or retard on the '79s but I've not had any adverse effects. Been running it capped for two years.
 
My car is a 78 and I also don’t know the difference between the two. For now I can cap it. I believe the advance improves both performance and efficiency at high revs. Technically the same thing, but you know what I mean.

From Wikipedia:
Vacuum advance works by using a manifold vacuum source to advance the timing at low to mid engine load conditions by rotating the position sensor (contact points, hall effect or optical sensor, reluctor stator, etc.) mounting plate in the distributor with respect to the distributor shaft. Vacuum advance is diminished at wide open throttle (WOT), causing the timing advance to return to the base advance in addition to the mechanical advance.

I think I could drill a port into the intake manifold and use that. I will have to shop around and see if there are better or smaller bungs than the one that came with my old cylinder head. It’s typically immediately after the throttle. Not sure if there is a hole already built into the DCNVA or DCNF carbs but I think there should be. Hopefully Steve will chime in.
 
A quick look at my intake manifold shows 3 Ports out the back and a welded port on top. The two on the sides appear to connect with the coolant passages, perhaps for cooling when the head doesn’t have the coolant passages already built in, or for manufacturability. The welded port on top lines up with cyl for runner. I’m thinking I could drill that back out, tap and create vacuum off it.
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Many carbs have a vacuum port that would serve without having to make changes to the manifold.

Yes you could also drill and create a vacuum port from the intake manifold.

You would never get vacuum from the head itself.
 
The vac nipple for my '79 carb'ed engine is on the carb itself (not the head nor manifold). Take a look for a brass tube that connects to the venturi area.
 
AKimball92 said:
I feel like I’m making this forum all about me... I’ve got another problem.

The head I’m using 4444407 is a 12 bolt 1500 head but doesn’t have a vacuum port. I am using a vacuum advance Ducellier distributor. Where can I pull the vacuum? Also I purchased the 36 DCNVA carb from Steve. Haven’t really looked at it yet and still fairly ignorant on carbs but it too might need vacuum.
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Typically vacuum for the distributor is taken from the carb, not the head. I would wait for the 36 DCNVA to arrive, and see what ports it has.
 
AKimball92 said:
The head I’m using 4444407 is a 12 bolt 1500 head but doesn’t have a vacuum port. I am using a vacuum advance Ducellier distributor. Where can I pull the vacuum?[/ATTACH]
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Vacuum ports are in the manifold and/or the carb, not the head. All the carb manifolds I have in my boneyard (none like yours, of course) have a vacuum nipple between the runners for #1 and #2 cylinders, opening into the plenum space underneath the carb. That's the one I use to draw vacuum for the vacuum advance.

The two ports into the coolant passages are for the lines to a water choke on a stock DATR/DATRA/DHTA carb.
 
It appears you are correct. I didnt mention the other welded bung between runners 1 and 2 in my new manifold from Steve. I will need to drill that out and tap it for vacuum.

I have the Carb already. There just isn't that much documentation on it online. I tried to search for data a while back when I got it and couldn't find much, gave up and wrapped it back up for when I was ready. No point in learning without the motivation of it being between me and a running engine.

Here are pictures of my old head and intake. You are correct EricH. The nipple is right where, very rusty so I will need to source a new one, probably brass from Lowes. My old head has all the ports possible, 2 to the coolant passages, one to the interior exhaust tube. strangly it also has the hole to the thermostat but the thermostat's hole is there but goes nowhere.

IMG-3701.JPG IMG-3696 (1).JPG

Either way the problem is mostly answered. I need to drill into the manifold between 1 and 2 and obtain a new vacuum nipple. Shouldn't be too difficult.
 
It is common for the distributor to be fed with ported vacuum from the carburetor rather than straight vacuum from the manifold. Ported vacuum is taken from right before the throttle plate, so that with the throttle closed it will be at atmospheric pressure. As you open the throttle slightly, you'll get max vacuum, gradually decreasing as you open the throttle further. Does the 36 DCNVA have a nipple for ported vacuum?

The rusty nipple at the back of the manifold in you picture looks big enough to be for a vacuum booster; is this manifold from an X1/9, or from some other Fiat SOHC application?
 
I'm with Bjorn. The dizzy vac is customarily a small one off the carb, right near the butterfly level of the main (primary) venturi. That's how it offers a different signal under varying conditions for the dizzy's advance. The vac port on the intake manifold is a large one, such as for the log that supplies a bunch of smog solenoids, brake booster (on other models), dash controls (e.g. AC models), etc. The vac signal from it will be different than from the carb.
To help locate the correct port on the carb, look for a small hole or brass pipe that aims directly toward the main throat and corresponds to a tiny hole on the inside of the venturi just below the butterfly valve. Blow through a test hose attached to each port until you feel the air coming out of that tiny hole inside. Hope I haven't confused it too much. Steve will be able to give you exact instructions when he has an opportunity to check in. I'm sure he welded that large port shut for a reason.
 
Thank you Jeff. It’s as clear as mud now. Actually that does help and I need to think about the time signals being different.

I’ll be bringing in he carb and really looking at it today. That should clear things up.
 
Usually the vacuum pickup for a distributor would be on the carb... and if you look at the DCNVA I think you will find two suitable points... you want the vacuum value to vary depending on throttle position.

Even better would be to dump the vac distributor and find one that is full mechanical advance as per european models of the X19.

SteveC
 
fiatfactory said:
Usually the vacuum pickup for a distributor would be on the carb... and if you look at the DCNVA I think you will find two suitable points... you want the vacuum value to vary depending on throttle position.

Even better would be to dump the vac distributor and find one that is full mechanical advance as per european models of the X19.

SteveC
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Thanks Steve, I knew you would have the answer. Is this carb in your book? Would I be able to have some PDFs of the associated pages?

Updating ignition is definitely in the plans. I would like to go pointsless at some point. For now a running car is priority. We all know these cars are never ending projects. As funds come available, the ignition is the first to get the makeover, then cooling, then some growing rust concerns.
 
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vacuum port on the carb base in the centre is the line which goes to the choke pull off diaphragm...to ensure this functions you'll need to drill a small hole between the throttle bores in both the phenolic spacer and also the alloy carb base in the manifold, if you look between the throttle bores on the underside of the carb you'll see the hole/port that needs to be supplied with a vacuum signal. the brass fitting on the side of the carb about half way up on the right (near the idle speed screw) is the one to attach a distributor vacuum line to.

SteveC
 
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