Mysterious Vacuum Hose, were to...?

[YellowHorse]

Since buying big blue from the member here, I finally took of intake filter to figure out why it runs 2k rpms at idle and hard to keep running while cold.

So the car has Holly 670 cfm street avenger Carb and what I found is that there are two vac lines not connected anywhere. Small line goes through firewall and thick line Ts off from intake plenum.

Am I right to assume that they need to be hooked up to the black canister ?
Also what's that canister is for?

 

[Steve McMahan]

Here is the 1973 Mustang 351 2v emission system I think you’re referring to:


The black can, I believe, is attached also to intake vacuum, and the outlet of the can connects to the HVAC system, which as I remember, a separate vacuum line that come through the firewall.

 

[rackerm]

That vacuum hose connects to the A/C system under the dash. I'll post a picture

 

[YellowHorse]

Thanks both you. My 73 has no AC so I could not confirm Vac lines to get my 71 corrected.

 

[YellowHorse]

So someone did few realy dum things with this 71 mustang. In addition to vacuum line not plugged in to AC canister, vacuum niple at the bottom of the carb was open. Had small hose dressed on the niple, but hose was not plugged.

Last owned did say that AC did not relly blown cold even after runing new lines and condenser/pump and of course engine ran rough. I suspect mechanic wanted to get the car on cheep after causing lits of headaches.

 

[YellowHorse]

Watching Autorestomod video, he states to not use ported vac on the side of the carb, but instead use vac niple on the bottom of the carb...for vacuum advance. Do you all agree?

8.3 min in to it

 

[mrgmhale]

Watching Autorestomod video, he states to not use ported vac on the side of the carb, but instead use vac niple on the bottom of the carb...for vacuum advance. Do you all agree?

8.3 min in to it

Sorry for the late reply, The oem distributors for 71 - 73 Mustang/Cougar all use Ported Vacuum for their distributor vacuum advance systems, unless the coolant temp goes too high (I think 215-220 degrees F or so). Upon the engine coolant getting to a certain excessively high level there is a Thermal Vacuum Switch that diverts intake manifold vacuum to the vacuum advance diaphragm in an attempt to try to help cool the engine.

There are some vacuum advance distributors that have dual diaphragms that have an inner (2nd) diaphragm.

I have attached a few files for you to reference. First, Mustang barn created a series of engine vacuum schematics (aka calibrations) for 1966 - 1972. I, with their knowledge and permission, consolidated all of their individual files into a single PDF file that is grouped by year, and sorted by engine. The next file is Volume 6 of the 1973 Mustang shop manual. In Volume 6 you will find a description of emission control devices, as well as a set of 1973 engine vacuum calibrations.

The original 1973 Volume 6 calibrations in the original shop manual did not include two calibrations for the 351 4v engine. I have those attached as a separate file, and my version of the Chapter 6 excerpt being attached already includes those 351 4v calibrations since I added them to my PDF file.

I inferred you are looking for engine vacuum schematics, not schematics for the HVAC system. If you do need the HVAC vacuum schematic let me know and I will dig it up.

Finally, in reading through the preceding posts it looked like "someone" (can't remember who) thought engine vacuum should be applied to an evaporative fuel vapor canister. That is not correct. There are three outlets/inlets on the evaporative fuel vapor canister. One (in between the other two) should have a plastic hood over it, and it is not connected to any hose as it is used to provide incoming air ventilation. The small inlet looks like the right size for an intake manifold or ported vacuum line, but it isn't. It is connected to the fuel vapor deliver line that leads back to the fuel vent at the top front of the fuel tank. Finally, there is another outlet that is about 1/2" or so in diameter. There is a flexible foil & paper hose that connects that outlet to the air cleaner housing. When the engine is running there is a little bit of vacuum that is present inside the air cleaner housing. That low vacuum pulls fuel vapors trapped by the charcoal granules inside the evaporative fuel vapor canister, and the fuel vapors pulled into the air cleaner housing are then pulled into the engine and burned. The entire fuel evaporative control system is well documents, with clear drawing, in the shop manual Volume 6 PDF file. I also recorded a video showing the fuel evaporative system, with narration, on my Youtube channel. Following is a link to that video:

https://youtu.be/n9woMnHByts


Another similar video is at:

https://youtu.be/ZasC4GH1XUo

 

[Big Red Mach 1]

I agree with mrgmhale . My car runs a lot better on ported.

 

[giantpune]

Watching Autorestomod video, he states to not use ported vac on the side of the carb, but instead use vac niple on the bottom of the carb...for vacuum advance. Do you all agree?

8.3 min in to it

The ported vs manifold vacuum for advance is a subject many folks feel strongly about, and any discussion about it online will lead to arguing and half the thread catching a ban.

I agree with the position that on a car built for a daily driver or street, if the distributor is getting its advance signal directly from the carb, it is best to use ported vacuum. If the motor is wild and built for the track, it may work more better with the distributor hooked up to full manifold vacuum. And there are some factory cars in the 70s with very intricate vacuum setups where the distributor is connected to the manifold vacuum, but it also goes through a complex series of valves and switches.

 

[YellowHorse]

Sorry for the late reply, The oem distributors for 71 - 73 Mustang/Cougar all use Ported Vacuum for their distributor vacuum advance systems, unless the coolant temp goes too high (I think 215-220 degrees F or so). Upon the engine coolant getting to a certain excessively high level there is a Thermal Vacuum Switch that diverts intake manifold vacuum to the vacuum advance diaphragm in an attempt to try to help cool the engine.

There are some vacuum advance distributors that have dual diaphragms that have an inner (2nd) diaphragm.

I have attached a few files for you to reference. First, Mustang barn created a series of engine vacuum schematics (aka calibrations) for 1966 - 1972. I, with their knowledge and permission, consolidated all of their individual files into a single PDF file that is grouped by year, and sorted by engine. The next file is Volume 6 of the 1973 Mustang shop manual. In Volume 6 you will find a description of emission control devices, as well as a set of 1973 engine vacuum calibrations.

The original 1973 Volume 6 calibrations in the original shop manual did not include two calibrations for the 351 4v engine. I have those attached as a separate file, and my version of the Chapter 6 excerpt being attached already includes those 351 4v calibrations since I added them to my PDF file.

I inferred you are looking for engine vacuum schematics, not schematics for the HVAC system. If you do need the HVAC vacuum schematic let me know and I will dig it up.

Finally, in reading through the preceding posts it looked like "someone" (can't remember who) thought engine vacuum should be applied to an evaporative fuel vapor canister. That is not correct. There are three outlets/inlets on the evaporative fuel vapor canister. One (in between the other two) should have a plastic hood over it, and it is not connected to any hose as it is used to provide incoming air ventilation. The small inlet looks like the right size for an intake manifold or ported vacuum line, but it isn't. It is connected to the fuel vapor deliver line that leads back to the fuel vent at the top front of the fuel tank. Finally, there is another outlet that is about 1/2" or so in diameter. There is a flexible foil & paper hose that connects that outlet to the air cleaner housing. When the engine is running there is a little bit of vacuum that is present inside the air cleaner housing. That low vacuum pulls fuel vapors trapped by the charcoal granules inside the evaporative fuel vapor canister, and the fuel vapors pulled into the air cleaner housing are then pulled into the engine and burned. The entire fuel evaporative control system is well documents, with clear drawing, in the shop manual Volume 6 PDF file. I also recorded a video showing the fuel evaporative system, with narration, on my Youtube channel. Following is a link to that video:

https://youtu.be/n9woMnHByts


Another similar video is at:

https://youtu.be/ZasC4GH1XUo

Thank you. Do you happen to have 1971 vacum to trans calibration?

 

[73inNH]

Last owned did say that AC did not relly blown cold even after runing new lines and condenser/pump

These cars have a vacuum actuated hot water valve on the heater hose. Sometimes vacuum is connected incorrectly or the valve gets gummed up and needs to be cleaned. This can prevent the heat from turning off, making the A/C warmer than it should be.

 

[Hemikiller]

The problem of ported vs full manifold is it's not like choosing a pair of socks, the engine and distributor has to be set up to run one, or the other.

I prefer using ported vacuum for vacuum advance. Others may have a different preference. You also may have difficulty getting the engine to idle down to a reasonable RPM using manifold vacuum.

Jeff also seems puzzled by the large port at the front of the carb, which if he bothered to RTFM, all would be explained.

 

[YellowHorse]

As found, vacuum was not connected to the HVAC. Might be the only issue, If no vac = open valve. Thanks for headsup though, definitely something to check. Plunger on that valve does move by hand.

These cars have a vacuum actuated hot water valve on the heater hose. Sometimes vacuum is connected incorrectly or the valve gets gummed up and needs to be cleaned. This can prevent the heat from turning off, making the A/C warmer than it should be

 

[giantpune]

Jeff also seems puzzled by the large port at the front of the carb, which if he bothered to RTFM, all would be explained.

I was thinking the same thing. If he were to RTFM, he would also see even holley tells you to hook the distributor up to the ported port.

Holley, the high performance folks and selling the carb that says "not legal for street use". They already dont have to care about emissions with that disclaimer. All they have to care about is performance, and they are recommending to use the ported vacuum.

 

[YellowHorse]

So i tried to check timing on my 71. Disconnected both vacuum hoses from the distributor. Car idle slowly fluctuated from 1,000 - 1,600 rpms and timing fluctuation was 14 - 30.
Vacuum was 14 - 21 (higher when rooms were higher).

Why would rpms and timing fluctuate if I discovered and pluged all off the vacuum?

 

[Doug's 73 Mach1]

Distributors also have a centrifugal mechanical advance that increases timing as engine rpm goes higher. That kicks in and gradually increases timing an usually maxes out in the mid 30s of advance. I think with different engines and distributors the rpm it starts increasing advance at varies as does the max advance. Distributors were use weights and springs under the points mounting plate to control this. Distributors can be "curved" to set the advance amount as rpm increases at different rpms. Perhaps your distributor was custom "curved" to increase timing at lower rpms than factory specs. Recurving distributors is a fairly common performance enhancement done by changing weights and springs. Heavier weights and or weaker springs advance the timing quicker as rpm increases.

 

[Hemikiller]

I'd keep looking for more vacuum leaks. Spray carb cleaner around the base of the carb, you can also use an unlit propane torch. Idle will normally change when you find one.

It also seems you have the Holley on a stock iron intake. Normally they seal fine, but I'd pull the carb and check the condition of the gasket. The carb pre-heat passage is below it, and given I see a flimsy Holley gasket on there, it could have burned through and be pushing exhaust gasses into the intake.

 

[YellowHorse]

I'd keep looking for more vacuum leaks. Spray carb cleaner around the base of the carb, you can also use an unlit propane torch. Idle will normally change when you find one.

It also seems you have the Holley on a stock iron intake. Normally they seal fine, but I'd pull the carb and check the condition of the gasket. The carb pre-heat passage is below it, and given I see a flimsy Holley gasket on there, it could have burned through and be pushing exhaust gasses into the intake.

View attachment 77940

Thanks. I will spray starting fluid and most likely pull carb off, as its the only way to set transition of the primary butterflies correctly. Also need allen screw to adjust secondary butterfly for idle.

 

[giantpune]

and most likely pull carb off, as its the only way to set transition of the primary butterflies correctly.

I set mine with the carb installed and the engine running. Connect a vacuum gauge to the ported vacuum on the carb. Then adjust the idle screw so there is no vacuum showing on the ported line, but as soon as you crack the throttle one little inkling, it shows vacuum.

IMO, thats gonna get you to the correct spot more reliably than flipping the carb over and trying to guestimate if you have exactly a tiny little square of the transfer slot showing.

 

[YellowHorse]

I set mine with the carb installed and the engine running. Connect a vacuum gauge to the ported vacuum on the carb. Then adjust the idle screw so there is no vacuum showing on the ported line, but as soon as you crack the throttle one little inkling, it shows vacuum.

IMO, thats gonna get you to the correct spot more reliably than flipping the carb over and trying to guestimate if you have exactly a tiny little square of the transfer slot showing.

So as soon as needle moves from 0 on ported vac, I am at correct spot?