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  1. #46
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    Quote Originally Posted by 78HZSBC View Post
    Would 77 likely be too big for my application? Reading the specs on the one i have now from memory is around 63.
    Obviously jets can be changed.
    Couple of reasons why i like this one is it doesnt have a choke system i dont need but mainly i like the idea of adjustable air bleeds as thats a problem i have now.
    I have to adjust the idle screw too far allowing the throttle plates to be held open a little too much, think this effects my throttle response from idle. Not a big issue but be nice to adjust this instead of drilling holes in the plates.
    Oh yeah also like the quick change vac spring set up also
    63 main jets seem about right for a 600cfm.

    Main jets for 750cfm is often in the 70-75 range primary for WOT tuning depending on main air bleeds and to a degree emulsion. Maybe they have a tiny pvcr. I wouldn’t be surprised if you end up with 70 - 71 MJ primaries and 80 thereabouts sec. Those 750 Street HP’s had .025” pri main air bleed and .036” sec mab and .071” pri idle air bleeds and .028” sec iab. Two corner idle stuff on a 4 corner carb. Easy fixed with .028” mab both ends and .070” starting point for iab all four corners. Really good, quality, economically priced hi-po carby. Certainly give it a good run to asses before diving into air bleed changes though.
    A vac spring kit would be good to dial in vac sec opening too.

    750 Street HP at the bottom. The ones I have seen have .071” pri iab.

    [img]https://i.ibb.co/YTBd9Qk/AE4137-E9-76-AB-45-AB-8-D65-79-FD9-A12-DAAA.jpg[/img]


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    Last edited by BasicQ; 13-10-2021 at 07:01 PM.

  2. #47
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    I dont know much about the air bleeds but just know that i can adjust it if i need to, most likely will just run the carbi straight out of the box and see how it goes before making any changes.
    Any yeah i have a vac spring kit already, tried a few on the 600 i have.
    I kind of like the feel of the secondary's kick in on the lighter spring but obviously not the correct one so didnt keep that one

  3. #48
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    The problem with the Holley vac sec system is there is nothing to counteract the bog when the secs open. Carter AFBs [ & Edel copied it ] have an ingenious starter cct in the secondary clusters that supplies fuel on initial sec opening. Like a low speed cct. QJs also had various iterations of it, but AFBs had it from day one, in 1957.
    Carter also, in the start up year of 1957 had a vac sec model. One year only, very rare, I have one. It was soon consigned to the dustbin of history, presumably because it did not work as expected...

  4. #49
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    hi
    would not going to a heavier spring fix this?
    As I read the situation opening early stalls the air flow dropping air speed and signal . I imagine this is more so noticeable on some than others depending gearing cam gear stall etc .

  5. #50
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    Thing is i havnt had a chance to really run with this yet to see how the different springs perform or notice any bogging when the secondary's open, hopefully next few weeks ill have it run in and oil changed and will see from then.
    There might be better carbies but most likely be a case of sticking with what i know

  6. #51
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    Quote Originally Posted by GtoGeoff View Post
    The problem with the Holley vac sec system is there is nothing to counteract the bog when the secs open. Carter AFBs [ & Edel copied it ] have an ingenious starter cct in the secondary clusters that supplies fuel on initial sec opening. Like a low speed cct. QJs also had various iterations of it, but AFBs had it from day one, in 1957.
    Carter also, in the start up year of 1957 had a vac sec model. One year only, very rare, I have one. It was soon consigned to the dustbin of history, presumably because it did not work as expected...
    Any vac sec bog on a Holley is tuning as swampy alluded to, not design. I’ve owned a few and never had a clue when driving of the opening point of the secondaries, certainly no bog, just as Holley intended.

    Bogs are self induced by the owner tuning it with light springs to be a poor mans mech sec. I doubt the Carter has been immune to the over zealous young hot rodder making good intended modifications to secondary operation that has resulted in compromised drivability. Great design doesn’t always prevent poor modifications and tuning.

    Like the AFB a correctly set up Holley vac sec will have a smooth, indistinguishable secondary operation. If punters want to ‘feel the secondaries kick-in’ then a vac sec isn’t the right choice for the reason you stated Geoff, as a disappointing bog may be the result.


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    Last edited by BasicQ; 14-10-2021 at 10:37 PM.

  7. #52
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    Basic,
    Of course Carters suffer like any other brand from over zealous tuners. A popular move was to remove the velocity weights from the secondaries in AFBs...which produced a bog...& then smacked you in the back when the secs kicked into gear. I was not talking about folks who modified carbs, I was talking about people who used them as they were designed by the maker.
    The fact remains that on a vac sec Holley, there is no initial secondary fuel flow when the sec blades open, not until the main system starts. Maybe this gets covered by a richened up primary system. The AFB system functions like a choke, which as we know requires very little engine rpm [ engine cranking speed ] to draw fuel.

  8. #53
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    Quote Originally Posted by GtoGeoff View Post
    Basic,
    Of course Carters suffer like any other brand from over zealous tuners. A popular move was to remove the velocity weights from the secondaries in AFBs...which produced a bog...& then smacked you in the back when the secs kicked into gear. I was not talking about folks who modified carbs, I was talking about people who used them as they were designed by the maker.
    The fact remains that on a vac sec Holley, there is no initial secondary fuel flow when the sec blades open, not until the main system starts. Maybe this gets covered by a richened up primary system. The AFB system functions like a choke, which as we know requires very little engine rpm [ engine cranking speed ] to draw fuel.

    Fair enough but my over all point was a correctly adjusted and operating Holley vac sec will not have a bog. If there is it is likely been incorrectly tuned into it via tinkering by someone who wants to feel the secondaries open or a modified engine that has a vacuum profile that demands the secondaries need dialing in different from out of the box. Opening of secondary is referenced at the primaries and when they signal secondaries to open that air speed is high enough and the opening (that should be) gradual enough that the mains start up happens easily enough to accommodate the additional airflow avoiding any bog. I highly doubt this design and operation that does not have secondary opening fuel compensation would persist for so long if it were flawed.

    I can kind of see how AFB might need that little bit of coverage due to its different secondary opening operation. As the air valve opens with the secondary throttle plates already open underneath there could be a momentary change in air velocity (and therefore signal at booster) through the carb with the area of throttle bore the primaries and secondaries already have exposed to the engine. A little bit of fuel compensation until the velocity recovers. Just a hypothesis as you would understand the operation better than I would Geoff.


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  9. #54
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    Basic,

    Just for general discussion. I have tried both 600 vac sec Holley & 625 Carter carbs & the Carters have better throttle response. No question about it; & better on a street car in my opinion. However, in a way, it is to be expected....
    Carter did something very clever with their 600s. They used smaller pri for better response & the larger secs for top end, which combined gave ~625 cfm. Pri bores are 1 7/16" & secs are 1 11/16". Holley 600 is 1 9/16" pri & sec.

    So the smaller pri bores enhanced response, as you would expect.

    Edelbrock tested a 600 Holley against a 625 AFB on a 1972 Chev 350. The 625 made 17 ft/lb more tq, 17 hp more & used less fuel doing it. This was BEFORE Edel started making AFBs & they were selling modified Holley carbs. I have the HP graph if anybody is interested, PM me your email address.

  10. #55
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    hi
    Alot to be said for only sizing carb to 100% VE [NA] compared to people going way oversize for the actual engine needs . Street-ability is hard to describe for some vs others who understand . Not always about the last 10 hp at 6500rpm .

  11. #56
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    Quote Originally Posted by GtoGeoff View Post
    Basic,

    Just for general discussion. I have tried both 600 vac sec Holley & 625 Carter carbs & the Carters have better throttle response. No question about it; & better on a street car in my opinion. However, in a way, it is to be expected....
    Carter did something very clever with their 600s. They used smaller pri for better response & the larger secs for top end, which combined gave ~625 cfm. Pri bores are 1 7/16" & secs are 1 11/16". Holley 600 is 1 9/16" pri & sec.

    So the smaller pri bores enhanced response, as you would expect.

    Edelbrock tested a 600 Holley against a 625 AFB on a 1972 Chev 350. The 625 made 17 ft/lb more tq, 17 hp more & used less fuel doing it. This was BEFORE Edel started making AFBs & they were selling modified Holley carbs. I have the HP graph if anybody is interested, PM me your email address.
    I agree the ‘ol Carter Aluminum Four Barrel is a more refined carb than a Holley but your test would be more valid or apples to apples if it were with a Holley spread bore with small primaries like the AFB.

    Sounds like Edelbrock were priming the public for something they had in the works at the time.


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  12. #57
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    Basic,
    No, it was an apples to apples comparison. Both companies had a choice in how they sized their carbs for total airflow, H chose equal size pri & sec bores.
    And no, I do not believe Edel had AFB carbs 'in the works'. Edel didn't start making AFB until the late 80s, I believe 1989 was the exact year. Carter was still making carbs well into the 1980s. The test I mentioned was on a 1972 engine & it would be reasonable to assume that it would have been a current engine or certainly not that old. The carbs tested were the #9625 Edel & #6619 Holley.

    In my 1986 Edel catalog, there are NO carbs listed. In my 1979 Edel catalog, there are nine Holleys listed. So I do not see how there could be any bias by Edel towards either brand of carb at the time of that test; if anything, more towards Holley because of their selling H carbs.

  13. #58
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    Quote Originally Posted by GtoGeoff View Post
    Basic,
    No, it was an apples to apples comparison. Both companies had a choice in how they sized their carbs for total airflow, H chose equal size pri & sec bores.
    And no, I do not believe Edel had AFB carbs 'in the works'. Edel didn't start making AFB until the late 80s, I believe 1989 was the exact year. Carter was still making carbs well into the 1980s. The test I mentioned was on a 1972 engine & it would be reasonable to assume that it would have been a current engine or certainly not that old. The carbs tested were the #9625 Edel & #6619 Holley.

    In my 1986 Edel catalog, there are NO carbs listed. In my 1979 Edel catalog, there are nine Holleys listed. So I do not see how there could be any bias by Edel towards either brand of carb at the time of that test; if anything, more towards Holley because of their selling H carbs.
    Here’s an apple

    [img]https://i.ibb.co/gdHZ7w9/D77-F2889-2-CB0-4250-92-AA-8-FD68-D6-A1208.jpg[/img]

    And a bit of insight into Edelbrock and AFB style carbs:

    How Edelbrock Created its Nearest Competitor

    "Around 1964'65, our friend, Bob Joehnck, said I should make an aluminum four-barrel intake for the Chevy. I said, 'Why? Chevy makes one already.' Then I thought about it and decided maybe he was right. So we make one, and Les Gaugh from Holley says he'd like us to try some of their carbs on our manifolds. They made a 780-cfm 3310 Holley carb that was used on the Chevelle—they only made about 200. So we take the 3310 and put it on our intake and it just runs great—it's perfect.
    "We go to HOT ROD, and they do an article. Holley never saw the article before it came out—they didn't know anything about it. They had planned their 3310 production for the following year at 200 units. When the article hit the newsstands, they sold 200 carbs in two hours. So they tried to figure out what's going on, and find out about the HOT ROD article, look me up, and the vice president of Holley calls me and is really upset. They want me to come to their headquarters. I had meetings in New York, and they were in Detroit, so I rearranged my flight and stopped in. They told me never do another article with their product without their knowledge. So that's how we initially got hooked up with Holley.
    "Holley started repping our stuff, and things were going well. When the new Blazer came out in 1973 1974, they were having all kinds of problems with the Holley 6619 carburetors. From the higher engine heat, the tops would warp and dump gas into the bowls. We had an intake and replacement for those carbs. Eventually, Colt purchased Holley. At this point, the reps were not happy, so they came to us and said that if we would give them the Edelbrock line they'd withdraw from Holley and take us. Well, as you can imagine, Holley was not happy. Then I went to Carter Carburetor and asked them to start making the AFB*. We calibrated our manifolds for the AFB. Once Holley found out, that's when they decided to get into the intake manifold business. But that's OK, we need the competition—it sharpened our act up."

    Vic Edelbrock Jr.
    HOTROD NEWS
    75 Years of Edelbrock

    https://www.motortrend.com/news/hrdp-1301-75-years-of-edelbrock/

    *I assume he is talking about a particular variant of AFB or Edelbrock start making the Edelbrock AFB specific manifold.

    So the test would have been to show results of testing of a manifold that is designed for AFB style carbies.


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    Last edited by BasicQ; 17-10-2021 at 01:32 PM.

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    Variants of the AFB. There were 505. Buuuuuut, the basic shape & design never changed. What varies were things like the boosters, pri & sec which are removable. They all have a # stamped on them & were essentially hand built for each engine. The original design had the 3 3/4" air clean neck, but at some point, I think late 50s/early 60s came the 'E' series which had the 5" air cleaner neck, same as Holley. These were used on Buick engines. The bodies were pretty much the same; I have fitted 5" tops to 3 3/4" bodies.

    Some of the above comments do not make sense. You calibrate the manifold to the carb? I would think the other way round. Maybe he meant the carb mounting pad. And asking them [ ? Carter ] to make the AFB......which had been in production since 1957. Carter was bought be Federal Mogul, must have been in the 1980s, because my 1980 Carter catalog has the owner as ACF industries, who had owned Carter for many years. F-M produced AFBs for a few years & then Edel started making them.

  15. #60
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    Quote Originally Posted by GtoGeoff View Post
    Variants of the AFB. There were 505. Buuuuuut, the basic shape & design never changed. What varies were things like the boosters, pri & sec which are removable. They all have a # stamped on them & were essentially hand built for each engine. The original design had the 3 3/4" air clean neck, but at some point, I think late 50s/early 60s came the 'E' series which had the 5" air cleaner neck, same as Holley. These were used on Buick engines. The bodies were pretty much the same; I have fitted 5" tops to 3 3/4" bodies.

    Some of the above comments do not make sense. You calibrate the manifold to the carb? I would think the other way round. Maybe he meant the carb mounting pad. And asking them [ ? Carter ] to make the AFB......which had been in production since 1957. Carter was bought be Federal Mogul, must have been in the 1980s, because my 1980 Carter catalog has the owner as ACF industries, who had owned Carter for many years. F-M produced AFBs for a few years & then Edel started making them.
    I agree it doesn’t read very well but the gist is they were breaking with Holley and talking with Carter around ‘73 - ‘74 and may well explain why they published a test that had the results contrary to what they sold.


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