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OK Guys,

I have read numerous posts regarding this and I think I have a pretty good idea how this switch SHOULD work and how it is connected to my dual port advance on my distributor.

According to my vacumn diagram, the bottom hose on the tree runs from the switch, tee's to the retard vacumn fitting on the distributor and then continues on to the manifold vacumn fitting. The question is, with it hooked up this way, how is the switch controlliing this particular vacumn line? It would seem that as soon as you start the motor, manifold vacumn will be retarding the distributor because of the tee in the vacumn line.

The problem I have is that I disconnected and plugged the system and timed the motor. Shut it down and reconnected the system and tried to test drive but the motor did not accelerate well and seemed to be trying to cut out. I stopped and pulled the ported vacumn from the carb and plugged it, then I pulled and pluged the manifold vacumn line. Test drove and the car ran fine!

Anyone know a test procedure for this vacumn switch in a "engine cold" state?
 

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Distributor Vacuum Control Valve Specifics

This is a very late reply but might help others having this same state of confusion regarding these 3-Port Distributor Vacuum Control Valves (DVCV). First of all, this topic can get really deep because there are so many different uses for DVCVs as well as many vacuum connection configurations that existed for these 3-Port valves. These valves are also know as a PVS (Ported Vacuum Sw), Vacuum Control Valve and Distributor Modulation Valve. They are used in various setups to either control emissions or increase idle speed during high engine temperature situations. The California Dist-O-Vac setup used them as well as the IMCO (Improved Combustion) setup for emission control purposes. The manner in which they were connected varied depending on the application for the valve, the engine it was installed in, the vehicle options (AC or Non AC, Automatic or Manual transmission, 4v or 2V, etc). It gets even deeper than this. Remember this was when the world of emission controls was first emerging and all kinds of different setups were being tried in order to satisfy the Federal emission regulations. In short – you need to know what year Mustang, what engine, in what state, and with what options to even have a chance of knowing exactly how your particular Mustang used and connected its DVCV lines.

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com
In the case mentioned here, a 1970 351C, I have a fair idea because that’s what I have. Mine, being a <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com
California</SPAN></st1:place></st1:State> car from <st1:City><st1:place>San Diego</st1:place></st1:City>, was equipped with the Dist-O-Vac setup. I now know how this DVCV was originally installed. I don’t know where Johnny’s 351C Mustang was manufactured, but even so, my research indicates that all 1970 351C DVCVs had their middle port always going to the advance diaphragm port on the dual diaphragm distributor. Understand that when these valves move, all they’re doing is either connecting the center port with the top or connecting the center port with the bottom. The temperature at which they do this depends on the application and year. When cold, the valve is connecting the center port with the top and the bottom port remains closed (or blocked). How this valving is utilized and plumbed is going to vary depending on whether you have the Dist-O-Vac setup or the IMCO setup or a setup that simply increases the idle speed when coolant temperature reaches 225 degrees.

In some applications, while a vacuum port may be allowing vacuum to enter its line, a bleed off port opens in a module downstream to render this vacuum ineffective for advancing the distributor. When you get into the electronic module functions of some of these setups, it really gets complicated and involves other factors like ambient temperature and vehicle speed as well. I’ve got over a dozen pages of info on these variations and frankly I still do not fully understand them all. I’m connecting mine to simply advance the idle speed when the coolant temp reaches 225 degrees, but on the exterior it’ll look like the Dist-O-Vac setup that was originally installed at the factory.
<o:p></o:p>
Hope this is helpful information for some of you.<o:p></o:p>
 

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Anyone know a test procedure for this vacuum switch in a "engine cold" state?
Too easy. The normal position of the valve is for the top and center outlets to be connected. Just connect a tube to the top outlet, and suck on it. Air should flow freely from the center outlet to the top. Connect to the bottom outlet. Air should not flow. The valve should open at about 220°F, closing the top outlet, and connecting the center and lower outlets.

The purpose of this valve is to expose manifold vacuum to the vacuum advance in an overheating engine, which advances the timing, which increases the idle speed, which spins the radiator fan and water pump faster at idle, cooling the engine. Simple, and effective, in low-speed traffic.
 

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I did explain that aspect of it and that's how I'm installing mine now. However - it was originally installed as part of the California Dist-O-Vac emissions setup that involved a speed sensor, temp sensor, an inline bleeder valve and an electronic module (next to the parking brake pedal) that would apply retarding vacuum to the distributor under a particular set of conditions. That jumble of components and conditions is anything but simple. Johnny’s DVCV application may have originally been used in the Dist-O-Vac or IMCO setup instead. He didn’t provide enough information to know.

P.S. - That's a good picture of a DVCV.
 

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but the distovac you mention was only on 351C 4V Cali cars.
mines an original 2V cali car and don't have it.

but all 351C's had the WP vacuum tree regardless where it was made.

FWIW I disconnected the WP vacuum tree in the 70's and the car runs great.
it only bumped up the idle about 150 RPM any ways. hardly noticable in traffic.
 

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<FONT face="Times New Roman">I have two basic schematics that apply to the 2V application of the DVCV. The one with the single diaphragm I believe is the setup that simply raises the rpms during temps of 225 degrees or more. I believe the 2V / Dual Diaphragm depiction is for the emissions (via the retard diaphragm) related setup, although there might be more to this setup than they are showing. However, neither of these stated their being particular to the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com

I've got a question for you: Did your bottom port of the DVCV connect to a FULL manifold vacuum source?
 

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yeah those diagrams are correct.

I never knew what depicted if you had a single or dual diaphragm can.

mines currently single going to ported vac off the carb.

my car runs great that ways and I wouldn't change it.
 

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<FONT face="Times New Roman">I have two basic schematics that apply to the 2V application of the DVCV. The one with the single diaphragm I believe is the setup that simply raises the rpms during temps of 225 degrees or more. I believe the 2V / Dual Diaphragm depiction is for the emissions (via the retard diaphragm) related setup, although there might be more to this setup than they are showing. However, neither of these stated their being particular to the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com

I've got a question for you: Did your bottom port of the DVCV connect to a FULL manifold vacuum source?
These dual diaphragm distributors, do they have two diaphragms with different diameters? I figured they must have, because off idle, vacuum on both sides is the same, so in order to advance the timing, the front diaphragm must be larger in order for the front advance side to "win".
 

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These dual diaphragm distributors, do they have two diaphragms with different diameters? I figured they must have, because off idle, vacuum on both sides is the same, so in order to advance the timing, the front diaphragm must be larger in order for the front advance side to "win".
Um, no. The "dual" means the rear half is sealed and capable of drawing vacuum, too, so "dual" as in "dual acting", like the pistons and cylinders on a steam engine. The single diaphragm is open on the back.

They do not have the same vacuum on both sides.

Here's one of the odder Ford circuits, 69 302 2V manual trans without AC-


Notice there is no DVCV installed. The front, or advance, side of the advance is connected to ported (venturi) vacuum. The rear, or retard side of the advance is connected to the manifold vacuum. At idle, and moderate cruise, there will be no vacuum to the advance, plenty to the retard, and since the advance is spring-loaded to full retard, the vacuum has no effect either way. As the throttle opens, the ported vacuum increases, and manifold vacuum decreases, advancing the timing. It would only be a momentary coincidence if the vacuum were ever the same on both sides.

Even with a DVCV, this is typical, ported advance, manifold retard. I use this example because it is extremely simple.
 

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Man Oh man 22GT, you must have every Ford diagram ever made ... and in High Resolution!
Thanks.
As a matter of fact I set out a few years ago to collect them all. Got tired of searching for them, and often not finding them. Pretty sure I succeeded in getting them all. Ford didn't make it easy, either. Different places in the manuals, and even different formats. 68-69 were charts, 70-72 were pictorial, then the 73 was a table that refers to diagrams of both circuit and pictorial. And the resolution on even the original prints often sucked. Many required extensive retouching.
 

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Dave: would you know which cars or engines got the dual and which got the single.
I cant find any rhyme or reasoning to who got what or whos supposed to have what,

shop manual is no help as all it lists is dizzy part #'s and specs
 

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The truth is, many of the re-touched, supplemented and at times even corrected diagrams and schematics that are available now thru forums like this are often much better than what Ford actually provided back in their day. Thanks for your efforts!

P.S. - Ever seen my revamped 1970 electrical Schematic?
 

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Dave: would you know which cars or engines got the dual and which got the single.
I cant find any rhyme or reasoning to who got what or whos supposed to have what,

shop manual is no help as all it lists is dizzy part #'s and specs
The Ford Master Parts Catalog would, at length, going through application tables, tell you.

Here's a simpler way. Look up your specific engine here, and look at the diagram. They are not generic, they are year, model, and accessory specific. If your car is diagrammed with a dual diaphragm, or a single, then that's how it came.

Glazier/Nolan Mustang Barn | Mustang Vacuum Diagrams
 

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.
still don't make any sense.
AFAIK all 351C's from 70-73 had the DVCV.

your site 1970 shows in 3 variations for a 351C one is specific for 2V (single advance) other 2 dont mention one way or another which carb its for.

im still confused on who should have what.

don't really care as im not changing my set up but it would be nice to know anyways
 

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Um, no. The "dual" means the rear half is sealed and capable of drawing vacuum, too, so "dual" as in "dual acting", like the pistons and cylinders on a steam engine. The single diaphragm is open on the back.

They do not have the same vacuum on both sides.

Here's one of the odder Ford circuits, 69 302 2V manual trans without AC-


Notice there is no DVCV installed. The front, or advance, side of the advance is connected to ported (venturi) vacuum. The rear, or retard side of the advance is connected to the manifold vacuum. At idle, and moderate cruise, there will be no vacuum to the advance, plenty to the retard, and since the advance is spring-loaded to full retard, the vacuum has no effect either way. As the throttle opens, the ported vacuum increases, and manifold vacuum decreases, advancing the timing. It would only be a momentary coincidence if the vacuum were ever the same on both sides.

Even with a DVCV, this is typical, ported advance, manifold retard. I use this example because it is extremely simple.

Are you sure about that? Unless these particular setups work totally different than normally, then the vacuum port in the carb is located just above the throttle blades, so that it doesn't get vacuum at idle, but gets full vacuum once the throttle is opened far enough. That way, the vacuum advance works as intended: as a load dependent timing adjuster but not at idle (for emission, idle quality, ease of starting, warm up or whatever reason).
Here's a graph that shows it:



The way you describe it, you would need to connect it to the smallest point in the venturi, like the vacuum source for the secondary stage of a vacuum 4V carb. It would also increase advance with both load and speed which would not make any sense, as you want less advance with more load and more advance for higher engine speeds but that is already controlled by the mechanical advance.
Ford did use this type of vacuum control on the Load-O-matic distributors installed in six cylinders, but they didn't have mechanical advance.

I found one picture of a dual advance vacuum unit. It's from the 80's, so I'm not 100% sure if it works the same as those from the 60's. Anyway, it has two diaphragms, with the advance one preloaded with a light spring and the retard one preloaded with a heavy spring. In normal off idle conditions, vacuum with be the same, but the advance side "wins", due ot the lower spring resistance (in combination with differences in effective areas).


 
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helmantel

i see you found the graph the guy generated on his pontiac i believe it was.
 

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Are you sure about that? Unless these particular setups work totally different than normally, then the vacuum port in the carb is located just above the throttle blades, so that it doesn't get vacuum at idle, but gets full vacuum once the throttle is opened far enough.
It's not that simple. And of course, running the advance to manifold would give full total advance at idle, instead of zero advance, to to mention it would eliminate the ability of the DVCV to control overheating.
 
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