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  1. #26
    FEP Senior Member qikgts's Avatar
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    Mike, I've got a few random questions I hope you don't mind answering...

    Is this one going to go back together with a secondary metering plate or are you going to go with a metering block conversion and are any of the mods specific to that plan? On that same tip... do you think any of those secondary metering plates with provisions for actual jets would work on these 4180's? https://www.summitracing.com/parts/QFT-34-2/

    Also, in your initial mapping, the bore size and venturi size are listed; how (what tool) and at what point (the physical spot) do you measure the venturi size?

    How about measuring the transfer slots; is that done simply with calipers?

    I'm guessing you're going to keep the annular boosters in the primaries; what differences in tuning do you expect you'll encounter with the annular's vs a different type?

    Also, are you going to add a idle speed adjustment screw so the need for a solenoid (or something else) as a throttle stop is eliminated, like the truck carbs have?
    '85 GT

    The other one... 2016 F-150 XLT Supercab Ecoboosted with 3.73's...

  2. #27

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    Absolutely do not mind at all.

    I'm thinking to go with a secondary block. Also, this one didn't come with a primary float bowl, and there's a shortage of side pivot bowls and the shorter bowl screws here right now, lol, so I'm also thinking I'll put center-feed dual-feed float bowls on it. As to the bowls, if anybody knows whether a factory Fox 5.0L air filter housing, or the dual snorkel deals, will clear the needle and seat adjusting nuts/screws of the center-feed dual-feed float bowls, I'd appreciate hearing about it. Regarding the jet-able plates: I wish they'd show the backside of it... The plate that came off this carburetor here is the style that isn't rectangular like most, but sort of V's narrower at the bottom... with that style of metering plate, idle fuel travels up it, through the secondary idle feed restrictions in the plate, enters the secondary idle air bleed passage up high in the main body (#6 in the upper image below), picks up and mixes with some air from the idle air bleed and heads straight down to the basement, the secondary idle mixture screws and transfer slots in the base plate. This is different than most. In contrast, traditionally, with regular rectangular metering plates or metering blocks and a carburetor body with passages drilled to suit them, the idle fuel mixed with bleed air travels back downward partially within the plate or block (#19 in the lower image below), then into what you see is hole #4 in the upper image below (these are not drilled in 4180's... hence the V-shaped metering plate and idle fuel entry only up high into the #6 holes), and then down into the base plate... #4 traditionally only leads to the base plate transfer slots, and tiny (~0.025") secondary constant feed idle discharge holes below them, below the closed secondary throttle plates... so that a small amount of secondary idle air:fuel is admitted for balance and so the fuel in the secondary bowl doesn't go stale if the secondary barrels rarely get opened up.




    For most precise accuracy, a divider (those thingies similar to what used to be used to draw a circle, but with both pins instead of one being a pencil holder) would probably work best to measure, at the smallest diameter down the throat, which is in the vertical neighborhood of the booster. I eyeball with a steel rule from above, and these are commonly sized 600cfm carburetors as best I can tell...

    The transfer slot length with a dial caliper's tail, yes, but the transfer slot width I gauge with a precision drill bit, from a #61-80 index.

    Yes, I'm not knocking out boosters. I like these annulars... they don't take up much space within the venturi = less restriction to airflow. I'm going to be shrinking the 0.044" primary main air bleeds down to about a traditional size of 0.028"... which will allow the boosters to begin their flowing from the main circuit at a sane load level/rpm (meaning over and above any cruise situation or even light part throttle acceleration, which should be the most part the department of the transfer slots, the idle circuit calibration, dialed in lean-best), and with about a #64 primary jet, providing a flat and steady WOT air:fuel mixture from their low rpm activation all the way to red line rpm, in contrast to their original calibration that would encourage early and rich low rpm activation and a leaning out at red line because of those big main air bleeds. Primary main circuit to be very carefully evaluated after all else is dialed in... might end up needing less jet... we'll see...

    I like adding a traditional primary idle speed screw, so yes, I'll be drilling and tapping to create that provision, but either scenario will remain able to have/use...

    Thanks for the questions
    Mike
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  3. #28

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    There are a number of omissions and outright mistakes in this image (and others, and wording) screen-shot from the official "4160/4180C Carburetors - Ford Parts and Service Division Training and Publications Department" manual regarding the idle/transition circuits within the 4180C, and my findings with them and my markings on this image based on my findings with a number of 4180C's are one of the mistakes... there is no "IDLE DOWN CHANNEL" drilled horizontally down low and connecting with the base plate. The drilling for the secondary idle air bleed up top is drilled straight down through the body and connects with the base plate, and there is no "IDLE CHANNEL" within the metering plate that heads downward after the idle feed restriction and connects with the previously mentioned imaginary "IDLE DOWN CHANNEL". These are common regular Holley 4160 features.




    So, "they" weren't REALLY concerned with the details of these things, or anybody (even technicians with these training materials) REALLY understanding and knowing them or how or why they work or why they do what they do WHEN they malfunction.

    And so... I'll continue to display facts and photos to back them up here, along this road to eliminating all of the supposed "refinements" to the basic, simple, efficient original Holley design and features.
    Last edited by Walking-Tall; 05-28-2018 at 11:00 AM.
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  4. #29
    FEP Senior Member qikgts's Avatar
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    Thanks for the details Mike. Really diggin' it!

    Does the manual describe the secondary main metering correctly?

    I found a pic of the back of that quick fuel plate... from Jegs... https://www.jegs.com/i/Quick-Fuel/793/34-2QFT/10002/-1

    Name:  34-2qft rear from jegs.JPG
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    '85 GT

    The other one... 2016 F-150 XLT Supercab Ecoboosted with 3.73's...

  5. #30

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    Hi Mike,
    Cool to see you work your magic. This is going to be a great resource for others.

    In regards to your air cleaner question, my factory dual-snorkel unit seemed to fit over my 4150-style carb just fine. I never looked under it to see how well it cleared. I can throw it on and get some hard numbers if you like.
    Thomas

    1985 Mustang GT - Build Thread
    347 (10.5CR, AFR 185's, PP Crosswind, Comp Custom Cam, Holley SA "670"), T-5, 8.8 w/3.55's, MM SFC's, T/A, PHB, LCA's, STB, KMB, Bilsteins, MM/H&R Springs, SN95 5-Lug, Cobra Brakes

  6. #31

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    I'd have to look. The secondary main metering is standard fare, minus the bit too big "jets" and the bit too small main air bleeds.

    Yes, that plate would work... simply taking drawn up idle fuel through the idle feed restriction and then straight into the hole that's the equivalent to #6 in the upper pic of the image above, under/past the secondary idle air bleed, and straight down through the main body to the throttle base plate's secondary transfer slot and idle mixture screws. You see the vertical outermost channels of that plate?... those are what aren't necessary for a 4180C. Most regular Holley carburetors would need those channels because they have the lower entrance into the main body (#4 in the upper pic of the image above) for secondary idle/transition air:fuel. I don't like the look of that notched clearanced-for-the-jets float though. I'd be making sure whatever looks hap-hazardly slopped onto the cut out notch to seal it is actually sealing fuel from getting into it...

    Quote Originally Posted by qikgts View Post
    Thanks for the details Mike. Really diggin' it!

    Does the manual describe the secondary main metering correctly?

    I found a pic of the back of that quick fuel plate... from Jegs... https://www.jegs.com/i/Quick-Fuel/793/34-2QFT/10002/-1

    Name:  34-2qft rear from jegs.JPG
Views: 179
Size:  36.0 KB
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  7. #32

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    Thanks, Thomas. I hope so.

    I figured they should clear. Probably no need. Thank you.

    Quote Originally Posted by 85MUSTANGTGT View Post
    Hi Mike,
    Cool to see you work your magic. This is going to be a great resource for others.

    In regards to your air cleaner question, my factory dual-snorkel unit seemed to fit over my 4150-style carb just fine. I never looked under it to see how well it cleared. I can throw it on and get some hard numbers if you like.
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  8. #33

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    The saga continues...


    Remember these guys?



    They aren't JUST restrictions, but more pressed-in lengths of brass tubing... ... now ousted by drilling down into the idle wells to a depth of where the backside of the primary idle feed restrictions are, directly behind the primary main jets... shoulda seen the muck that came out with them AFTER having been through a thorough cleaning... not a good sign for when these are on the operating table at rebuild time and things are not getting all opened up like I'm doing... There's an inherent problematic pattern or theme I'm seeing that goes along with all of this secretive, "anti-tamper" business here and there in these, and it's that they are quite anti-thoroughly-clean-able all throughout. For these idle wells within the primary metering block, there's two exits for any possible debris to be removed at cleaning time... the 0.028" idle feed restrictions behind the main jets, or the idle air bleed passage, 2nd from up top of the block. I cleaned the daylights out of this block and it's passages, and blew lots of compressed air through both above-mentioned ends of the idle well, and muck remained and came out when I removed the pressed-in brass tubes... which I again see no reason for their presence... drilled passages suffice, and submerged idle feed restrictions do the restricting, the metering of necessary idle and transition fuel...


    Look what went previously unnoticed... silly me, figuring they must have pre-drilled "e-bleeds", booster air correction bleeds, clocked 'em to direct at the main air bleed wells, and pressed the brass tubes into the main wells... NOPE...












    So the tubes were put into the main wells, an approximate 1/8" hole existed or was drilled on the jet side of the block at an angle aiming at the primary main air bleed wells, which are only drilled from the top down to about the fuel level, and then I assume (because I can't really measure without likely destroying a tube to get it out) an approximate 0.028" bleed drilled through the other side of the brass tube and into the primary main air bleed wells, for connection with the primary main air bleeds... albeit this single air correction bleed is about 1/8" above normal float bowl fuel level...


    Traditional efficient functioning Holley carburetors have either... "e-tubes" within the main wells with small bleeds AT and/or BELOW the fuel level, a single bleed in the air well into the main well, or a second bleed about 7/16" below the upper at fuel level... like the lower two bleeds shown as #22 in the middle image of the image above.

    For now, I haven't decided what's down the road for the above... besides that I will be carefully drilling out the lead balls from the jet side and measuring the size of the booster air correction bleeds that are drilled into the main well brass tubes... they should be about 0.028"... stay tuned...
    Last edited by Walking-Tall; 05-29-2018 at 02:37 PM.
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  9. #34
    FEP Senior Member qikgts's Avatar
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    Quote Originally Posted by Walking-Tall View Post
    Yes, that plate would work...
    Soooooooo, since it would work, do you see any advantage to doing the block conversion over the plate w/the jets (discounting possible issues with the modded float)?

    This thread needs it's own website (or book)... lol

    Thanks a ton for sharing all this Mike!
    '85 GT

    The other one... 2016 F-150 XLT Supercab Ecoboosted with 3.73's...

  10. #35

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    Well... a Holley with a secondary block, 4150 style, sure looks cooler, lol... but no... eether, either... I assume the plate is cheaper than the block conversion kit?

    Happy to be trying to do this. Thank you for following.


    Thank you to Jim. The base plate we'll now be able to use to continue to refurbish this 1985 Mustang 4180C Holley carburetor arrived here today.




    There are a bunch of carburetor builds and rebuilds in the queue before I can get back to this, but when I do, I'll completely disassemble this base, including the throttle shafts for snugging up later with new teflon strip bushings where needed, and all four idle mixture screws removed, everything... then the bare base will get cleaned real good... after that I'll measure all of the machined idle/transition circuit holes and slots, and proceed, with pics of all steps...

    Stay tuned...
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  11. #36

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    You're very welcome! A cheap investment for the information you're providing!
    Jim DeAngelis
    Cornucopia of Useless Knowledge
    Connoisseur of Dearborn Ferrous Oxide
    '83 GT hatch, currently under the knife

  12. #37
    FEP Senior Member qikgts's Avatar
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    Quote Originally Posted by Walking-Tall View Post
    Well... a Holley with a secondary block, 4150 style, sure looks cooler, lol... but no... eether, either... I assume the plate is cheaper than the block conversion kit?
    I think the plate is a few bucks cheaper unless of course you already have the block, tube, etc.

    Quote Originally Posted by FB71
    A cheap investment for the information you're providing!
    Ultimately, as FB71 has already done Mike... Please PM or email me and we can discuss a "donation" toward your R&D costs . I'd like to help out here too.
    '85 GT

    The other one... 2016 F-150 XLT Supercab Ecoboosted with 3.73's...

  13. #38
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    Find someone with a vapor blasting cabinet, and that carb base will look like it was never used. Look into Vapor Honing Technologies. Check out their videos on You Tube.

  14. #39

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    Quote Originally Posted by qikgts View Post
    I think the plate is a few bucks cheaper unless of course you already have the block, tube, etc.



    Ultimately, as FB71 has already done Mike... Please PM or email me and we can discuss a "donation" toward your R&D costs . I'd like to help out here too.
    Okay, yes. Regarding the tube... In most cases I've been using the new style cup seals instead of o-rings for the fuel bowl transfer tube, and whatever length is needed of regular 1/4" tubing... this gets completely rid of the possibility of the problem of those o-rings sometimes not sealing...

    If you happen to have or see a primary float bowl with the 7/16" tube elbow for venting to the carbon canister like in the original application, I'd appreciate hearing about it, and would acquire it if not too much $.
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  15. #40

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    Quote Originally Posted by dynodon64 View Post
    Find someone with a vapor blasting cabinet, and that carb base will look like it was never used. Look into Vapor Honing Technologies. Check out their videos on You Tube.
    Thanks, Don. I'll check out the tech when I get a chance. I've already mostly cleaned up this disassembled base... pics in new post to follow...
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  16. #41

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    Got a chance (between being up to my eyes with others, mostly GM Holley 4-barrels, including a few Holley vacuum secondary and double pumper spread bores, and some original '60's GM muscle Holley 4-barrel carburetors) to disassemble and clean up the 4180 base and parts...


    Primary bores:



    Secondary bores:



    Cleaned up throttle shafts and plates, and there will be new teflon bushings for like-new snug, friction-free throttle shaft rotation:



    Idle mixture screws and springs cleaned up... they'll be getting new o-rings:



    When I get a chance next, I'll measure each of the orifices and the transfer slots and see where we're at and what needs doing...


    ... an odd/interesting vacuum source function with these... I believe it's for connection with the distributor's vacuum advance? The hose nipple at the front of the carburetor base (this is viewing the base bottom) is shown at the top in the area I've lit up to see it better. So, there's a small amount of full manifold vacuum at idle, with one hole below the throttle plate, and another (vacuum-leaking, reducing) hole above the throttle plate at idle... which would then become a source of increased vacuum signal as the throttle is opened, similar to how "ported" vacuum functions...




    That's it for now. I'll keep pluggin' away as I can.
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  17. #42
    FEP Senior Member qikgts's Avatar
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    Quote Originally Posted by Walking-Tall View Post
    Okay, yes. Regarding the tube... In most cases I've been using the new style cup seals instead of o-rings for the fuel bowl transfer tube, and whatever length is needed of regular 1/4" tubing... this gets completely rid of the possibility of the problem of those o-rings sometimes not sealing...
    Got it. Good solution.

    Quote Originally Posted by Walking-Tall View Post
    If you happen to have or see a primary float bowl with the 7/16" tube elbow for venting to the carbon canister like in the original application, I'd appreciate hearing about it, and would acquire it if not too much $.
    Please PM me an address to ship to, Sir. I've got what I think is a very nice specimen coming my way and I'll turn it around to you after I verify it's all good. Thanks again for the ultra deep dive into these carbs Mike!
    '85 GT

    The other one... 2016 F-150 XLT Supercab Ecoboosted with 3.73's...

  18. #43

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    Quote Originally Posted by qikgts View Post
    Please PM me an address to ship to, Sir. I've got what I think is a very nice specimen coming my way and I'll turn it around to you after I verify it's all good. Thanks again for the ultra deep dive into these carbs Mike!
    PM sent, Sir Steve
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  19. #44

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    Happy to report the base that Jim sent must have been, as they say, made on a Wednesday, because all of the slot machining is consistent side to side, with both primary transfer slots measuring 0.026" wide and 0.235" long, and both secondary transfer slots measuring 0.025" wide and 0.345" long... unlike the (broken) base that came with this carburetor here.

    After the above measuring, and some flat surface sanding of the top and bottom surfaces for further cleanup and true-ness, I drilled and tapped 10-32 for a traditional primary idle speed screw location if somebody doesn't want to bother having the idle solenoid in place. Either option is still there. Assembled the base with teflon bushings out back and throttle shafts and plates with new screws today. Idle speed screws set as: secondary - 1/4 turn open from fully shut in their bores; primary - approximate square transfer slot exposure below the primary throttle plates... all so far in fine condition to proceed...






    Still haven't had a chance to get back to the primary metering block... that's next... stay tuned
    Last edited by Walking-Tall; 07-05-2018 at 10:32 PM.
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  20. #45

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    I would like to just briefly say... 1838 views right now, and only a couple guys have had something to say within the thread. I would thoroughly enjoy it if anybody has anything they would like to say or add or ask here...
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  21. #46

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    Assembled the base with teflon bushings out back and throttle shafts and plates with new screws today.
    What do you mean with teflon bushings out back? On mine in order to get a good idle and minimize the off idle stumble/surge I have the primary idle screws adjusted at 3 1/4 turns out on the passenger side and 2 turns out on the drivers side. So, are these teflon bushing your talking about go on the throttle shafts where they go through the base plate to seal air leaks? I'm the original owner of a 1985 GT with 125K on her.

  22. #47

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    Thank you for the question. Most or all Holley 4-barrel secondary throttle shafts have channels in them for the nylon/teflon ribbon bushings that they come with right from brand new, that establish them being snug and to seal and for friction free rotation... and after a time, they wear, and the secondary throttle shaft becomes loose in it's base plate bores. The fix is replacing them with new ones. This base has good clearances. The primary shafts don't come with the ribbon bushings. If I'm working with a carburetor where there's too much clearance between the primary shaft and the base plate bores, sometimes adding some used (or new, if very loose) bushings tightens up the clearance. There are also channeled areas where they can be positioned if needed.



    Here's a closer look at the secondary throttle shaft and where the thin strip bushings go:





    Here's a pic from AllState Carburetors of a new replacement bushings set:





    So, yes for sealing, and for proper running clearance.



    Some possible reasons for primary idle mixture screws ending up 1-1/4 turns out different (which is an awful lot of difference. Normally, they are the same (or very close) number of turns out):

    - Yours' passenger side - idle feed restriction a smaller size than the other, or it or the path through the metering block or main body on the passenger side has some blockage and/or smaller sizing throughout the circuit... or an area combination of the two primary idle air bleeds (inside choke shroud and outside choke shroud) on the passenger side that's more (allowing more air into that circuit) than the driver's side...

    - Yours' driver's side - circuit restrictions sizing-wise, opposite of the above ^ ^ ^ ... or possibly primary idle air bleeds/passages debris/blockage on that side...
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  23. #48

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    Thanks for the reply. Now that I can get replacement parts I’ Order a couple of sets. Any way to seal the primaries?
    By the way with the idle adjustment screws at those settings I get a study 18 1/2” of vacuum.

  24. #49

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    The primary shafts don't come with the ribbon bushings. If I'm working with a carburetor where there's too much clearance between the primary shaft and the base plate bores, sometimes adding some used (or new, if very loose) bushings tightens up the clearance. There are also channeled areas where they can be positioned if needed.

    The steady idle vacuum you're getting is good, but the mixture screw position discrepancies indicate something is jacked up in the carburetor. The best example I can give of this phenomena is a Holley 650 double pumper recently refurbished, where upon disassembly one mixture screw was found to be very much so turned out further out than the other... and (lack of) quality control and manufacture of newer stuff is why... the image below is of a traditional Holley idle air:fuel discharge hole (controlled upstream by the mixture screw in the metering block) that was never fully drilled through, leaving only an 0.018" passage for idle air:fuel to get through:



    ... where the idle vacuum was pulling idle air:fuel properly through the other, this one had no chance in hell supplying enough, and it's mixture screw was turned out much more than the other... and I guarantee it could not have idled worth a darn from day 1... after that was remedied, the passage hole drilled fully through, everything worked like it should... the mixture screws are equally sensitive and adjusted outward the same amount of turns for best idle.
    Mike
    1986 Mustang convertible 3.8L ---> BUILD THREAD
    1983 Mercury Cougar 3.8L LS
    1986 Ford Thunderbird 5.0L ELAN
    1966 Ford Fairlane sedan 200-6
    1966 Ford Fairlane GT (390ci 4spd)
    1981 Mercury Marquis Brougham
    1980 Capri RS Turbo
    1971 Mustang Fastback
    1974 Pontiac Luxury LeMans

  25. #50
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    Walking-Tall,
    I have been following your project with great interest and appreciate your efforts very much. However, I don't have any Holley carbs (yet), just Motorcraft 2150's, so no experience and wouldn't know what to ask. So I won't clutter up the thread. I suspect there are many others in the same situation. Thanks for sharing your knowledge. We're out here learning, quietly.

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