Vacuum port for distributor?

Hi,

is it correct that the vacuum port in the picture below is for the distributor vaccum advance?



Thank you, Manfred

I've got mine plugged and ran my dizzy vacuum to the carb. Sorry I didn't answer your question, but heres a link that may:

http://www.mustangbarn.com/72vacuum.html

Find the vacuum diagram that fits your setup. Dual diaphram vs single etc...

Does your engine have a Distributor Vacuum Control Valve (DVCV) on it? If so, check out this link also:

http://www.stangnet.com/mustang-forums/788354-what-thing-my-water-pump.html

Hope this helps you as much as your questions have helped me. I'm now thinking about making my vacuum system as close to stock as I can make it.

Thanks,

DJ

Yeah, this is the one that uses that port.

http://www.mustangbarn.com/images/vacs/72%20351C%204v%20with%20dual%20diaphragm%20distributor,%20distributor%20vacuum%20deceleration%20valve,%20NASA%20Ram%20Air,%20and%20ported%20vacuum.gif

Yeah, this is the one that uses that port.

http://www.mustangbarn.com/images/vacs/72%20351C%204v%20with%20dual%20diaphragm%20distributor,%20distributor%20vacuum%20deceleration%20valve,%20NASA%20Ram%20Air,%20and%20ported%20vacuum.gif

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Awesome! I did a little more research and if you no longer have the DVCV on your water pump/neck, then you can either get one on fleabay for up to $69.99 USED Or, you can get a new one with lifetime warranty from Borg Warner part# EC970 for $30+ or a cheaper replacement from STD part# PVS14. These are called "Ported Vacuum Switch" but exactly the same as Distributor Vacuum Control Valve (DVCV)

I've got mine plugged and ran my dizzy vacuum to the carb. Sorry I didn't answer your question, but heres a link that may:

http://www.mustangbarn.com/72vacuum.html

Find the vacuum diagram that fits your setup. Dual diaphram vs single etc...

Does your engine have a Distributor Vacuum Control Valve (DVCV) on it? If so, check out this link also:

http://www.stangnet.com/mustang-forums/788354-what-thing-my-water-pump.html

Hope this helps you as much as your questions have helped me. I'm now thinking about making my vacuum system as close to stock as I can make it.

Thanks,

DJ

Click to expand...

Thanks,

the vacuum diagrams really helped. I think best describes my setup since I have no DVCV and a single vacuum advance distributor. This means I will directly connect my vaccum advance to that port.

Thanks, Manfred

Hi,

is it correct that the vacuum port in the picture below is for the distributor vaccum advance?

Thank you, Manfred

Click to expand...

Manfred, That is a manifold vacuum port. Given the Accel distributor design, you can use that port. Chuck

Manfred, That is a manifold vacuum port. Given the Accel distributor design, you can use that port. Chuck

Click to expand...

Thanks, will do.

- Manfred

That should go to the DVCV on the water pump, to switch from ported vacuum to manifold vacuum at idle should the engine start to overheat. On a '72 351C, it also had a T-fitting to a vacuum control valve on the drivers' side valve cover. This was part of the IMCO system which would switch on manifold vacuum to the retard port on a dual-diphragm distributor (which I see you do not have) under certain conditions. I just run mine straight to the DVCV - I get the overheat protectiion without that power-robbing emissions crap.

As you say you have no DVCV and a single diaphragm distributor, you can use that port for full manifold vacuum to the distributor and plug the port on the carb, or use the carburetor port and plug that one. With no DVCV, only one vacuum source can be used.

On that port it will increase your timing at idle (might vacuum at idle/cruise). Ported vacuum is the opposite, it will get higher as engine load in increased. You car will act differently depending which port you use. (and your initial timing and where you set it will be different). It's important to understand how each works and what it will do to the vacuum advance on distributor timing.

Thanks guys, I understand (in theory) all your explanations about manifold and ported vacuum and what the difference is. What I still have to find out is which one to prefer in my situation.

I read in another thread (I even think it was on the other site) that, performance and mpg wise, manifold vacuum should be used and that ported vacuum is only for emission purposes.

I played with the ignition advance over the weekend but didn't get conclusive results. My idle is lumpy (term???) which I understand might indicate a vacuum leak.

My problem is, I do not know how smooth the idle can/shoud be since I don't have anything to compare it with. Engine rpm varies by 50-100 and the vacuum by 1-2 inches during idle at 500 rpm. If I set the idle to 800 rpm it somehow smoothes out. The engine has been rebuild 2000 ago but has been sitting for 10 years since then. However, I have installed all new gaskets before it went into the car. I think I will try the carb cleaner for leak testing (never did that before) and maybe take a video of the idle and come back for your judgement ;-)

Thanks, Manfred

message 27 by 72h code in this thread (and lots of other posts in this thread) give good tips on tuning up.

http://www.7173mustangs.com/thread-runs-like-crap?page=3

You need to get yourself a vacuum guage.

If it isn't idling steady and you have your vacuum advance on manifold vacuum, it will make it run even funnier since the RPM change will cause a vacuum change which causes a timing change which causes an RPM change.... and so on.

Get it idling good without the distributor vacuum hooked up first.

Thanks guys, I understand (in theory) all your explanations about manifold and ported vacuum and what the difference is. What I still have to find out is which one to prefer in my situation.

I read in another thread (I even think it was on the other site) that, performance and mpg wise, manifold vacuum should be used and that ported vacuum is only for emission purposes.

I played with the ignition advance over the weekend but didn't get conclusive results. My idle is lumpy (term???) which I understand might indicate a vacuum leak.

My problem is, I do not know how smooth the idle can/shoud be since I don't have anything to compare it with. Engine rpm varies by 50-100 and the vacuum by 1-2 inches during idle at 500 rpm. If I set the idle to 800 rpm it somehow smoothes out. The engine has been rebuild 2000 ago but has been sitting for 10 years since then. However, I have installed all new gaskets before it went into the car. I think I will try the carb cleaner for leak testing (never did that before) and maybe take a video of the idle and come back for your judgement ;-)

Thanks, Manfred

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Manfred, Since the engine was rebuilt it is very likely the cam was replaced with a non-stock cam with some more overlap, duration, and lift. If this is true the idle speed will need to be higher than stock, require more initial timing than stock, and may be a bit "lumpy" at idle. The distributor you have is designed to use manifold vacuum and is adjustable for total advance as well as rate of advance. I'm assuming the carburetor is working properly (1-2 turns out on the idle mixture screws, less than .030 inch of the transfer slot exposed below the throttle blade). With no vacuum going to the distributor, hook the vacuum gauge to manifold vacuum and connect the timing light. While watching the timing lower the idle speed from about 1000 RPM until you see the timing stop retarding, the mechanical advance is now not engaged. Set the timing to about 10 degrees watch what the vacuum gauge indicates. you may have to decrease idle speed again to keep the mechanical advance disengaged. Set idle mixture screw for highest STEADY vacuum and reset idle speed to provide the idle smoothness you want, reset idle mixture screws. You may have to repeat this a few times to determine how much initial advance the engine wants to have (12 degrees, 14 degrees, etc.). When you are satisfied with idle speed and quality check total advance with the vacuum advance disconnected and plugged. It should be about 32-36 degrees. If it is not you will need to adjust the distributor to obtain the timing you want. Now drive the car to see if if it runs the way you think it should. If not try a different timing setting 2 degrees at a time. Do you have any specifications on the camshaft and carburetor? Chuck

The carb is a Holley 4160 (1850-3) 600 cfm with vacuum secondaries.

The distributor is a Accel 34000V single vacuum dual point unit.

The cam spec sheet is as follows:



Can the specification of the camshaft be attributed to the idle I have?

The following is a video captured by my son. It shows the idle rpm and vacuum reading during idle.



Rpm varies between 500 and 900 while the vacuum gauge reads 9 to 12 inch Hg.

During the video, the vaccum advance was disconnected from the distributor and the initial timing was set to 6 degrees.

After I read that a vacuum leak can contribute to unstable idle I had checked for such a leak before we took the video. Initially I disconnected and plugged as many vacuum lines as possible:

- disconnected brake booster and plugged port at carburetor

- disconnected PCV and plugged port at carburetor

- disconnected vacuum line to RAM air plaps and plugged it

- disconnected vacuum line to air cleaner and plugged it

- vaccum line for distributor advance was connected to vacuum gauge

I then sprayed brake cleaner around the base of the carb where it meets the intake. Likely, I sprayed all other parts of the carb without getting any indication of a vacuum leak. Initially I had forgotten to plug the line to the air cleaner which indicated a vacuum leak by jumping the idle rpm when spraying near the open end.

As you can easily see, I'm far from achieving a steady idle. Do I still have a vacuum leak I didn't find, is it the duration of the camshaft or something else?

I will follow the procedure outlined above by Chuck tomorrow.

Thank you, Manfred

Manfred, It looks to be a Summit cam. It is somewhat more aggressive that the stock M code cam (you car is aM code isn't it?). Try starting at 14-16 degrees initial advance. Keep total (without vacuum advance connected) at 34-36. Expect decent idle to be 850-950 RPM. Chuck

Don't forget to check front and rear of intake for a leak.

looking at the video the vacuum gauge is showing an issue with your valves.

it looks like poorly seated valves maybe sticking. The arm is swinging back and forth slowly.

try one thing first: on the holley make sure the idle Air bleed screws are setup at a good starting point.

turn engine off:

Turn both air idle bleed screws to clockwise to close them, Count how many turns Holley had them set at from the factory.

DO not bottom out the screws, close them slowly and the stop the second they bottom out do not apply much pressure when turning them(prevent damage to the screws)

Next Count 1 1/2 turns out on each side from the bottom out point.

This will reset the Air bleed mixture for Idle.

Now if the engine is too lean at idle it may act the same on the vacuum gauge with erratic idle and pulsing vacuum readings.

under load it can do this also if too lean.

start engine and see if there is a change in the vacuum needle. with any after market cam there will be flicker to the idle vacuum reading, some are very lumpy no matter what.

If the idle is better and the vacuum is steadier, then you can start to tune the Idle Rpms under load and fine tune the idle air bleeds.

you want to make sure somebody is in the car with the foot ont he brake, have the car in gear with the vaccum gauge hooked up.

your looking for Max Vaccum reading at the correct Idle Rpms. everytime you play with the idle air bleed screws you will need to re-adjust the idle RPM screw and go back and forth.

with car in gear and engine running. vacuum advance off.

start at say 675 - 700 rpms, and slowly close the idle air bleed screw watch the vacuum gauge and listen to the engine, watch the vaccum gauge as you close it to see if the vacuum rises a little, the second the engine rpms start to drop open the screw a little and match the setting with the other air bleed screw, let the engine settle and retest and double check the idle rpms try to keep it at a steady number.

if you note the vacuum gauge has settled lower then you started then open them up a little the idle rpms will come up and you will need to re-adjust the idle rpms again, keep watching the vacuum gauge and see if its higher. When you get close to optimal, moving the idle air bleed screws in and out 1/8 to 1/4 a turn will have almost no effect in dropping or raising the idle rpms of the motor, and the vacuum gauge shouldn't fluctuate much.

Now in the garage with all the gauges hooked up and everything at optimal you may think your done, but your not. because you will have to test drive it and see how cranky it is. most likely you will have to open up the air bleed screws 1/8 of a turn off optimal to get a decent idle quality when sitting at a stop sign or light for a few minutes after the engine is all warmed up.

temperature/weather/humidity it will all effect the engine one day you may find its running great the next day its 80% humid out and the engine is running like poop.

basically the idle air bleed vacuum reading is just a starting point to set and you always end up fiddling with it after driving the car for a while and seeing how it reacts. i can tell you the optimal vacuum reading and leanness to the fuel mixture at idle is not good if you have to make a Heavy brake stop, good chance the engine will stall out on you. so you have to richen it up just enough to make the engine happy, every engine is different no one setting is good its going to become more of a feeling when you tune your own car.

I'm constantly playing around with my timing and accelerator pump shot and trying what happens to the engine when its a touch too lean or too rich its the only way to learn.

enough wall of text from me. First make sure those holley factory settings on the carb are in the ballpark at 1.5 turns on the screws, then see how far off the carb came and if your vaccum gauge shows improvement.

If there is no change you may need to start looking into pulling the valve covers and making sure the rockers are closing the valves all the way.

if you have a hydraulic lifter may want to see if they are sticking for some reason, perhaps loosen the rockers and see if the valves were fully closing.

you could perform a leak test on the cylinders you blow air into the cylinders with the valves closed on the power stroke and if you have more then 8-10% leakage you know you have problems with the valves or rings. could be a bad valve job if that is the case. but try some tuning first and see if there is improvement.

there could also be an issue with the primary and secondary butterfly being too open on the primary and exposing the transition slot then you get this imbalance in the carb and it could also show up as a slow flicker to the vaccum reading.

Run off a ported vacuum port on the carburetor, not manifold vacuum.

Run off a ported vacuum port on the carburetor, not manifold vacuum.

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Can you (or someone else if they like) explain the pros and cons of running the distributor advance on ported vs manifold vacuum? I have read strong recommendations for manifold vacuum.

Thanks, Manfred

Manifold vacuum is high at idle and no load (cruise) situations.

Ported vacuum is low at idle and increases with load on the engine (accellerating)

At idle, if attached to manifold vacuum a vacuum advance will add advance and then once you put load on the engine it will stop trying to advance. Keep in mind that there is also a mechanical advance so if you lose vacuum advance it won't drop below what the mechanical advance is providing.

At idle, if attached to ported vacuum a vaccum advance will add no advance and then once you put load on the engine it will start to advance the timing. I don't remember if it adds to the mechanical advance or if it can only override how far advanced the mechanical advance is. I do know that it cannot go higher than total mechanical advance.

So, for example, if you are at 3000 RPM and you are at max mechanical advance and you put a load on the engine then if you are hooked up to manifold vacuum it doesn't matter since the mechanical is providing all of the advance and if you are ported vacuum it doesn't matter because you can't go past maximum mechanical advance.

At say, 1800 RPM you will not be at max mechanical advance. If your on mandifold vacuum then it may be adding addition advance over what the mechanical advance provides (I don't think it is cumulitive and this depends on your curve). So when you put on a load you may actually decrease the overall advance. If you are on ported vacuum you may increase your advance.

What works best for you depends on the engine, your initial advance, your curve, your manifold vacuum, how you have the vacuum pod set, what you want to do with the motor, etc. I really don't think there is a 'right' answer.

I hook it to ported but I have often considered using manifold. Clevelands like a lot of inital timing, especially with a hotter cam. This causes starting problems. If I used manifold I could decrease the initial timing, it would start easier, once started the manifold vacuum would pull the timing a little higher. There is enough initial timing that a drop off of vacuum advance probably wouldn't make much difference. The down side to all of this is the manifold vacuum isn't constant and changes as the motor warms up etc.....