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  1. #26

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    Here are some circuit images:








    First thing to check with Edelbrock carburetors is that it's "low speed jet" (idle feed restriction in Holley-speak) sizes (the hole size in the end of it's brass tubes) are the same side to side (they are sometimes not, a screw up)... and then brass setscrews can be drilled/tapped for to install in the "Idle Bleed"/"2nd Idle Air Bleed" holes in the boosters' castings, and then sized accordingly to make a world of difference in being calibrated best for YOUR combination.

    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/

  2. #27

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    Yes I have read up on changing the size of the bleeds and IFR a little and I understand that increasing or decreasing the air bleeds a tiny amount will make the mixture leaner/richer.

    But isn't that essentially what the idle screws are doing...or are these bleeds tuned to get the mixture just right and the screws give the proper idle air/fuel volume (keeping it around the 1.5 turns out etc) ?

    So if I get what your saying this can be used to tune up the just off idle (light cruise) circuit I was talking about while allowing the idle mixture to be tweaked bit richer or leaner etc ?

    I'm a bit confused then where the size for the cruise metering rod comes into play then. I assume it is at some further throttle point where it draws directly from the main jet? And then further throttle yet will lift up the metering rod and you get your power setting ?

    Interesting...I will have to take a good look for these things when I have the lid off my carb next time to try and find these ports.

    Thanks

  3. #28

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    No, and then yes, you're right, the idle mixture screws control and set the idle air:fuel volume that the engine likes best to idle at.

    Yes, the combination of a good size "low speed jet" for the combination, and an idle air bleed sized (usually greater than factory size) for best light part throttle acceleration, cruise, and even further light part throttle acceleration, is where the super-tuning is at, for sometimes pretty astounding cruise fuel mileage and nice crisp part throttle acceleration is at. Each and every idle air bleed change requires adjusting the idle mixture screws with the engine fully warmed up, because what gets to them will change a little bit by changing the idle air bleed size...

    The bottom line is that carburetor manufacturers would like you to believe that there is a 'take it out of the box, bolt it on, shut the hood, and go!" scenario... there isn't any such scenario, a luck of the draw at best... things are always calibrated on the safe-rich mediocre side of things, because they can't predict the potential thousands of different vehicle combinations their carburetor might be going onto... tuning to work best is our job...

    Correct, further/deeper throttle opening acceleration, where there's enough airflow then going through the venturi to begin the booster flowing, the main circuit flowing, is where the larger diameter of the metering rod dictates how much goes through the main jet... and then later, deeper yet into the throttle or wide open throttle is where the smaller diameter of the metering rod dictates how much gets through the main jet...

    No problemo, you're welcome - good luck with it
    Last edited by Walking-Tall; 05-08-2020 at 09:58 AM.
    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/

  4. #29
    FEP Super Member cb84capri's Avatar
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    I haven't heard of anyone modifying air bleed sizes on an afb/avs before. What size set screw do you use? I wonder if there are jets available that could be installed there?

    One day, I would like to get a hold of an AVS2 carb with the annular boosters. Or perhaps install annular boosters into mine.

    Cale

  5. #30

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    Ok gotcha...slowly the big picture sinking in

    If i were to try to lean up the very light throttle a bit (which I do think is a bit rich currently) which idle bleed would you enlarge...is there a preference between the 1st and 2nd etc ?

    Also if I analyze right then enlarging the idle air bleeds (leaner mixture) for very light throttle AFR adjustment would then cause the idle screws to need to back out a bit (become richer) to maintain the same idle AFR ?

    What AFR's do you typically go for in this very light area ?

    I think currently my idle screws are set around 1.25 turns so perhaps this is telling me I could go leaner etc. It seems at this point that my very light throttle AFR is almost same as where i set my idle.

    Sorry for all the questions. Appreciate the info !!

  6. #31

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    Quote Originally Posted by cb84capri View Post
    I haven't heard of anyone modifying air bleed sizes on an afb/avs before. What size set screw do you use? I wonder if there are jets available that could be installed there?

    One day, I would like to get a hold of an AVS2 carb with the annular boosters. Or perhaps install annular boosters into mine.

    Cale
    You'd have to check the existing hole size to be sure, but I believe 6-32, which would allow up to a 0.0625" (1/16") maximum size air bleed hole...

    - 6-32 = tap drill size #36 (0.107") = 1/16" flat-to-flat brass socket setscrew hex drive, so up to a 0.063" maximum bleed hole (most likely sufficient in an Edelbrock)

    - 8-32 = tap drill size #29 (0.136") = 5/64" flat-to-flat brass socket setscrew hex drive, so up to a 0.078" maximum bleed hole (potential possible need...)

    - 10-32 = tap drill size #21 (0.159") = 3/32" flat-to-flat brass socket setscrew hex drive, so up to a 0.094" maximum bleed hole (nice and bigger to deal with for tuning, what I put into a Holley if it has the larger bleed bosses... but the need for such a bleed hole size in an Edelbrock is not likely...)

    Also, anybody wanting to go this route of super-tuning, get brass (FAR easier to drill through than steel/other, especially with the smaller, precision, more fragile smaller size drill bits) cup-point socket setscrews, because it makes drilling the bleed hole nicely centered when drilled from the cup point end... PLUS, there's never anything good can come out of steel or something else by chance getting swallowed into an engine...
    Last edited by Walking-Tall; 05-08-2020 at 11:33 AM.
    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/

  7. #32

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    Quote Originally Posted by at_the_junkyard View Post
    Ok gotcha...slowly the big picture sinking in

    If i were to try to lean up the very light throttle a bit (which I do think is a bit rich currently) which idle bleed would you enlarge...is there a preference between the 1st and 2nd etc ?

    Also if I analyze right then enlarging the idle air bleeds (leaner mixture) for very light throttle AFR adjustment would then cause the idle screws to need to back out a bit (become richer) to maintain the same idle AFR ?

    What AFR's do you typically go for in this very light area ?

    I think currently my idle screws are set around 1.25 turns so perhaps this is telling me I could go leaner etc. It seems at this point that my very light throttle AFR is almost same as where i set my idle.

    Sorry for all the questions. Appreciate the info !!
    As you can see in the diagram and photo above, the 2nd would be easiest to add adjust-ability to and get to to tune.

    Yes, usually, idle mix screws would need to be turned out a tad if idle air bleed is enlarged, and as a rule the idle mixture screws should always be readjusted with the engine fully warmed up after an idle air bleed change.

    AFR's - super-tuning involves finding the point in light part throttle acceleration that is too lean, where the vehicle will surge or "trailer hitch" (and there's no cause to be concerned about this light amount of load on the engine), and then work back the other direction in small steps reducing the bleed size until there is no protest from the vehicle under those conditions... then you've found darn near to absolute perfection for the combination...

    The idle mixture screws will end up wherever they end up. That can be an indication but it's far less important than all of the vehicle's carburetor's off-idle/transition function, which is most normal/regular driving.

    I appreciate the questions.
    Last edited by Walking-Tall; 05-08-2020 at 11:27 AM.
    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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    Well I got to take a break from working on this for a week or two...wife says other projects more important LOL

    I ordered the new step up spring kit in the meantime and will update with what I find.

    Cheers

  9. #34
    FEP Super Member cb84capri's Avatar
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    Is there an echo in here? I think my wife tells me that every time I go near my Capri or Camaro, haha!

    Keep us posted with how those work out for you!

    Cale

  10. #35

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    Well I finally got my spring kits last week and a bit of time to work on it. The cross border mail is extremely slow these days

    I put in the blue springs which should give me enrichment from 12" to 8" range. I verified the brass tubes (IFR) on the carb are the same size. The 2nd IAB in the booster measures about 0.055" with a number drill bit but I never modified it yet. Thinking of going a bit bigger to get the transition circuit a bit leaner yet.

    Also put in the 1425 jets in my secondary to try and lean up the WOT. I think the blue springs will richen it up sooner and I may find the AFR a bit rich still in the power mode. Hopefully go for a drive tonight to see.

  11. #36

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    Well i did some testing last night and the blue spring appears to be worse

    They are acting more like an 8" or 7" spring vs 12". The lean spot is worse and lasts longer at light throttle (seeing AFR 17 at times) so I went back to the silver edelbrock springs which seem to behave much better.

    Kind of baffling why the higher rated springs seem to go the other way with the enrichment. Perhaps this quadrajet spring kit is not really interchangeable with the edelbrock for some reason (slight differences in the carb/power pistons etc?) Not sure...looking like a $50 mistake LOL.

    The smaller secondary jets (1425) did improve the WOT to AFR 12.4 at 6K in third so could probably go one more size smaller. I also moved the accel pump linkage to the bottom hole which seemed to provide better response too.

    Overall the driveability is pretty good. The more I play with it the more I feel that running a bit lean on the light throttle is probably fine, maybe even better for cruising fuel economy.

  12. #37

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    So latest update I decided to put in some 1418 rods (0.070 X 0.057) to further lean up the power mode keeping cruise the same. The very light throttle lean spot is still there but it does not seem to present any driveability issues at all so I think its fine. When you step on it further it richens up quickly and way you go.

    I realized I mistakenly moved the accelerator pump linkage to the wrong spot (farthest from pivot) which was less shot so I put it on the top hole closest to pivot which is supposed to be more shot. I was also going to increase the idle bleeds for the transition a bit but decided it was probably good as is.

    Still seeing very low 12's or high 11's for AFR on WOT so I think I could try going smaller yet on the secondary jets. Waiting for parts

    All this certainly leaned things up from original that's for sure. I need to put some miles on it to see what kind of mileage I'm getting and what the plugs look like longer term.

    So this is what I have installed now and it is working quite well in my opinion for the combo.

    1426 primary jet - 1418 metering rods (0.070 X 0.057) with silver step up springs (highest), Acellerator pump link on top hole closest to pivot
    1425 secondary jets

  13. #38

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    Well I went for a couple of longer drives with the car to test my tuning out.

    For the first 100 miles I kind of beat on it testing things on the back roads and then headed out on the highway for a longer trip trying to burn off a full tank of gas. Driving at a steady 75 mph and 2300 RPM for a couple hour trip it was cruising AFR around high 14's and low 15's for the most part and still responded well to throttle if you wanted to speed up or when climbing a hill etc.

    To my surprise when it was all said and done I went 260 miles on about 12 US gallons of gas for a mileage of 21.6 mpg...or 11L/100km for us Canadians I am pretty sure I never got anything close to that kind of mileage before. If I hadn't beat on it for the first hundred I'm sure it would have been much better...so needless to say I'm happy with that !!.

    Obviously the effort to tune and lean up the carb has improved the economy and I am happy with the way the car runs overall...so I think I'm done making any more major changes and calling it a victory for now. As a bonus and I learned a lot in the process too.

    Thanks for everyone's help and comments !!

  14. #39
    FEP Super Member cb84capri's Avatar
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    Thanks for posting up your experiences! I'l steer clear of the quadrajet spring kit. I wonder what effect (if any) shimming the silver springs inside the piston would have. That is some pretty great fuel economy. I can't get my car to cruise that lean at 75mph with the 4.10 gears, but it runs about that afr at 55mph in 5th. Problem for me is keeping my foot out of it. I did get mine to hit 19.8 mpg coming home from NC through flat Ohio last year.

    You might want to try enlarging the accelerator squirter nozzzles next if the lean tip in starts to create a stumble. Then you may want to take some stroke out.

    Good job!

    Cale

  15. #40

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    Thanks will have to kind of monitor what different conditions bring. Its probably time to think about changing the cam so I can start all over haha !!

    The WOT is still rich in my opinion so will probably still re-jet secondary lower to see if I can get it a little closer to 13 or so. Without the wideband for feedback I would probably not have been confident to just keep leaning it out that far from the stock calibration. It seems to me the stock calibration is set quite rich for the mass market with more radical engines and I guess to be on the safe side opposed to lean.

    I have 3.08's in the rear so it is geared more for speed than low end for sure but my 5th gear is the 0.72 set I think. Anyway it works out to 2300 rpm at 75 but seems to be a lean burning machine at that spot. Not sure what pure city driving will yield for mileage yet but can't imagine why that won't be much better too.

    However I will say it is nicer to be wondering why your gas guage doesn't seem to be moving as opposed to wondering if you have a hole in your tank

  16. #41
    FEP Super Member cb84capri's Avatar
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    I wouldn't target 13:1 with a carb. Multi port injection sure, but the fuel distribution isn't even enough for that with a carb in my opinion, and what is being communicated at the gauge is an average of a bank of cylinders. If I ever see over 12.8 at wot, I put a bigger set of jets in the secondaries. Then again, my engine is 10:1 compression with iron heads so your engine is probably a lot less likely to hurt anything.

    It's a nice feeling to get reasonable mileage out of a carb for sure, lot of people out there nowadays make it sound like it's impossible.

    Cale

  17. #42

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    The most radical of engine combinations can also be dialed in to achieve real efficient lean-best idle, off-idle, cruise, and even leaner light part throttle transition as a stock or mild combination, with the addition of one more tuning variable. MUCH easier with a Holley... it might take some extra creativity to add to an Edelbrock or Carter carburetor, but the addition of PTSR's (primary transfer slot restrictions) is where surprisingly efficient running can also be found with even the most radical of combinations... because of the opposite amount/levels of manifold vacuum at idle versus off-idle/cruise/transition that a more radical combination produces.

    For instance - a rumpity-rump idle radical combination might have say 6"Hg at idle, requiring a comparatively richer idle feed / idle air bleed calibration... but at off-idle, cruise, and light part-throttle transition, the manifold vacuum will usually double or even triple, pulling that much harder on the idle/transition circuit (= richer - the opposite of what we want for those high vacuum, low load situations (which are also the product of higher rear axle gearing))... so the ability added to be able to "pinch off" and adjust the amount of idle/transition air:fuel that gets to the transfer slots is where the same surprisingly good fuel efficiency and crisp snappy light part-throttle response can be had.

    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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