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  1. #26
    FEP Power Member Jerry peachuer's Avatar
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    is your choke set where you want it ?

    Rich idle and choppy sound has me guessing this is possibly what's disappearing as the.choke opens

    Just a thought

  2. #27
    FEP Power Member Jerry peachuer's Avatar
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    Thanks for posting chart

  3. #28

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    Quote Originally Posted by Walking-Tall View Post
    I can explain the science of why it isn't better. I'm just tired of hearing this robotically stated, and really would like it's case being made, if there is a case to be made.
    Ported vacuum does give a more defined feel when letting off the gas. Manifold vacuum gives a softer return and may tend to "hang". Engine braking with ported vacuum can also be stronger.

    One isn't inherently better than the other, it really comes down to preference.

    If you prefer the feel of ported vacuum and are concerned about engine heat then run the vacuum advance through a "red" ported vacuum switch. The "red" switch will put manifold vacuum to the vacuum advance if the engine starts to over heat. Ford started doing this back in the 60's. It's often dismissed as emissions junk but is actually a clever and simple way to prevent over heating.
    Last edited by mrriggs; 12-04-2016 at 12:38 PM.

  4. #29

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    Quote Originally Posted by mrriggs View Post
    Ported vacuum does give a more defined feel when letting off the gas. Manifold vacuum gives a softer return and may tend to "hang". Engine braking with ported vacuum can also be stronger.

    One isn't inherently better than the other, it really comes down to preference.

    If you prefer the feel of ported vacuum and are concerned about engine heat then run the vacuum advance through a "red" ported vacuum switch. The "red" switch will put manifold vacuum to the vacuum advance if the engine starts to over heat. Ford started doing this back in the 60's. It's often dismissed as emissions junk but is actually a clever and simple way to prevent over heating.
    Preference, yes. I have never found anything predictable enough in how it runs when using ported vacuum. How much and when, due to throttle angles, are highly variable. Ported vacuum's birthplace was with "emission control", to lessen certain exhaust byproducts, "Nox" for sure. I find that phrase with the word emission sometimes seems to automatically get grouped with or confused for the word efficiency. Similar things happened with lowered initial timing settings, neither having much to do with efficiency but with emission control. The reason for my preference of always defaulting to using manifold vacuum is what's always presented as more predictable and tune-able to me, cooler predictable engine temperatures, and a slower and smoother and leaner idle possible, especially when there's more than a stock camshaft with choppy/lower vacuum levels in the equation.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  5. #30

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    With a bigger cam, manifold vacuum has always worked better for me.

    With a stock cam, I've had issues with manifold vacuum. Sometimes the throttle plates are closed so far, there is almost no airflow to carry the fuel. On a standard carb, the transfer slots may end up completely blocked so they don't respond fast enough when the throttle is opened.

  6. #31

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    well that wasnt the issue, the car killed after a short while. I was able to replicate it in the driveway by revving the engine real quick and when it would drop back to idle it would try to do. i decided what the heck and switched over to ported, adjusted everything out and 100 miles later it still has not died and CONSISTENTLY idles at 750-850 whether ac is on or not (with manifold i had to idle it to almost 1k in order to use ac without stalling).

    it could just be that i never found the carbs "happy place" tune wise while hooked up to manifold vacuum, but ported vacuum does seem to run better...

  7. #32

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    Quote Originally Posted by hawk232 View Post
    well I adjusted the idle to be a little richer and, granted I only drove about 10 miles, the car never died. hopefully that was it!

    also, when its cold the car lopes like it used to but once to operating temp it smooths out.
    Don mentioning a seeming too lean idle mixture, is entirely applicable with anything. The above findings also indicate lean situations, corrected with either richer mixture screw settings or upon warm-up.

    Something's odd. Might we see an under hood pic?
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  8. #33

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    unless there is more to the idle mixture than the screws, i dont think thats it. before switching to ported i richened it up 1/4 turn at a time until it was stumbling and the problem remained (did the same in the lean direction).

    i will post and underhood pic this afternoon when i get home from work

  9. #34
    FEP Super Member gr79's Avatar
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    Interesting post on ported vac.
    Tuning

    I say give the engine what it needs and you are happy with response.
    Timing, etc.
    Sound like its close, correct config or not.
    I believe an engine can have a 'personality' a little different others just like it.
    Factory timing specs are a baseline and sometimes have to be tweeked a bit.

    Similar scenero:
    1969.. parents new family 69 Chevy wagon 350/300/auto.
    Same engine as in a Nova SS of that year.
    Chugging sound from tailpipe at idle. Cam sound?
    We kids started learning how to work on tuning up our muscle cars.
    Talked dad into letting me get my hands on it.

    Adjusted timing up a little from factory setting.
    Smoothed out and ran much stronger w/better mpg. No other changes.
    So i redeemed myself a little from the other crap i pulled back then.

    He did not care for the simple Quadrajet vac mod trick to pop the secondaries open quick.
    "Put it back the way it was". 2 minute job.

  10. #35

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    Quote Originally Posted by hawk232 View Post
    unless there is more to the idle mixture than the screws, i dont think thats it. before switching to ported i richened it up 1/4 turn at a time until it was stumbling and the problem remained (did the same in the lean direction).

    i will post and underhood pic this afternoon when i get home from work
    With Edelbrock carburetors (the same as with most others) the idle mixture screw adjustment admits, through intake manifold vacuum below the throttle plates, a volume of the idle circuit air:fuel mixture. In Edelbrock carburetors, that idle circuit air:fuel mixture is first dictated by two idle fuel jets/restrictions and two idle air bleeds before arriving at the transfer slots and idle feed discharges (where the tips of your mixture screws are). The original sizing of those jets/restrictions/bleeds (and clean and clear passages throughout) should give satisfactory function and/or adjust-ability with idle speed and mixture adjustments. Adjusting the idle mixture screws says how much volume of that idle circuit air:fuel mixture gets admitted below the throttle plates to mix with the incoming air around the throttle plates by your idle speed setting.




    Some things to check/adjust from Vic's manual:




    IMHO, I think there's more going on with your situation than a ported/full vacuum situation difference, because there isn't normally such horrendous differences (stalling and such with vacuum advance connection) in how something runs simply depending on which vacuum source the vacuum advance is connected to. *Edit: some more thoughts... unless the vacuum advance diaphragm is leaking. THAT would cause a meaningful difference (vacuum leak) in idle quality (or stall out) if connected with full manifold vacuum at idle, as well as effect the idle speed setting and idle mixture screw adjustment necessary. I don't think a leaky diaphragm would be as evident off-idle when connection to ported vacuum activates it... hoping to see the distributor and vacuum lines in the pic too...

    Looking forward to the picture...
    Last edited by Walking-Tall; 12-06-2016 at 02:03 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  11. #36

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    here are a couple of pics




  12. #37
    FEP Power Member Jerry peachuer's Avatar
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    Appears you tried both ways but didn't touch the dizzy ??

    One will have constant vaccum man vac and the ported or timed will only work when throttle opens (its above the throttle blades)

    Don't take my advice look at the chart posted above

    Off throttle at idle the two options are (polar opposite )so you will have action on one and not the other (at idle) which will require a choice by you to pick and re time and tune your carb

    That's how I see it ,I'm not a mechanic but do tinker on my own stuff nor am I saying that's your issue but the chart doesn't lie for what's really happening (At idle )

    So if your pulling vac and switch to vac only as blades open then I believe your not dialed in for those 2 extremes (see chart) at idle

    Just a thought

    To me looks like you took pictures of option A and option B but the dizzy is in same place
    Why does that matter ?
    Your dizzy is vac advanced when you loose vac it advances mechanically if your not having a signal of vac at idle your stuff is mechanically doing what it's ment to do at idle which isn't ideal add RPM and it's more vital
    Throw in a vac secondairies carb and it tosses in more gas it thinks your near or at a demand for high load or WOT (low vac)

    Sounds like your very close one way and not so close the other that should point you in a narrow direction than looking at the whole puzzle

    Again this is my guess as too the night/day of option A port and option B port
    That chart says a lot


    good luck

  13. #38

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    i read the instructions and watched the videos. when switching from manifold to ported you HAVE to re-tune the carb (so i did). I didnt play with timing as nothing i have read indicates i should mess with it (it at 11*BTDC with vac line disconnected).

  14. #39
    FEP Power Member Jerry peachuer's Avatar
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    Yeah that makes sense I guess

    I guess where my head was at when you DO hook up your vac line to the two options
    You will have vac and the other option you won't until the throttle blades start to open so it will or could mess with your initial advance

    I personally never used ported so can't really comment accurately on that

    Good luck

  15. #40
    FEP Member Mgino757's Avatar
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    Ported will give a small amount of vacuum at idle, in my experience. It just relies on a moving volume of air past the throttle blades to generate the vacuum instead of what is below the closed throttle blades. It delivers the most vacuum under partial throttle operating conditions, like cruising. This gives more vacuum advance, which requires less throttle while cruising, which in turn uses less fuel.

    By having less vacuum advance at idle, this allows you to have the throttle blades open a little more without having excessively high idle. This also gives a more stable mixture.
    Last edited by Mgino757; 12-07-2016 at 01:16 PM.
    1985 Mustang GT conv. modified 4180C, Weiand Street Warrior intake, equal length headers, true dual exhaust, 3.55:1 8.8'' rear end, 2003 V6 T5, Ford Racing 10.5" clutch.

    1998 Mustang GT auto. PI swapped. Daily beater

  16. #41

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    Quote Originally Posted by Mgino757 View Post
    Ported will give a small amount of vacuum at idle, in my experience.
    The Mustang 4180 carburetor has a "hybrid" spark port that feeds a portion of manifold vacuum to the distributor when the throttle is closed. I don't know of any other carburetors that have this feature.

  17. #42
    FEP Member Mgino757's Avatar
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    Aye, you are correct. I forgot about that minor detail. The rest still applies though.
    Last edited by Mgino757; 12-07-2016 at 02:18 PM.
    1985 Mustang GT conv. modified 4180C, Weiand Street Warrior intake, equal length headers, true dual exhaust, 3.55:1 8.8'' rear end, 2003 V6 T5, Ford Racing 10.5" clutch.

    1998 Mustang GT auto. PI swapped. Daily beater

  18. #43

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    I would suggest you dive into the dizzy.
    Limit it to about 26* mechanical advance.
    Springs that have it all in at 3000 rpm's.
    Make sure the dash pot is adjustable. Set it so you have about 9* of advance at 5 in. of vacuum.
    After that tune carb.
    After that hook up vac advance to either ported or manifold. ( I suggest manifold )

  19. #44

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    Quote Originally Posted by Mgino757 View Post
    Ported will give a small amount of vacuum at idle, in my experience. It just relies on a moving volume of air past the throttle blades to generate the vacuum instead of what is below the closed throttle blades. It delivers the most vacuum under partial throttle operating conditions, like cruising. This gives more vacuum advance, which requires less throttle while cruising, which in turn uses less fuel.

    By having less vacuum advance at idle, this allows you to have the throttle blades open a little more without having excessively high idle. This also gives a more stable mixture.
    Ported vacuum gives you nothing at idle, UNLESS your idle speed setting is too high... which throws correct idle mixture adjustment right out the window. It does not deliver "the most vacuum under partial throttle operating conditions", it delivers exactly the SAME amount of vacuum, off idle, that manifold vacuum does under operating conditions.
    Last edited by Walking-Tall; 12-07-2016 at 10:29 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  20. #45

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    Do you know the advance curve of that "HEI", and how much the vacuum advance advances?...
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

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