Characterizing and Tuning BJ/BK Dual Quad Clones

[Thumperbird]

Starting a new thread just for fun to more specifically address playing with a set of Carl's BJ/BK dual quads.  For those new to this build, I have a set of replica (or so I thought) BJ/BK carbs mounted on an Edelbrock RPM Air Gap Dual Quad Manifold with some custom offset spacers.  Carbs are facing forward, BK is in the rear.  Build is a moderate 445 stroker with quality internals, hydraulic roller, moderately worked Edelbrock heads, headers, sitting in a 1965 Thunderbird with C6 and gears midway between street and strip.  I will try and keep this thread more to the form of the DMAIC process though I don't have a ton of measurement tools to work with in the way of performance measurements (no dyno for one).

Basically out of the box I am struggling with very rich idle, decent smooth cruise, rich pulse followed by lean on moderate to heavy acceleration.  My intention is to work these carbs over as hard as needed over the winter and through next summer to maximize proper response at all throttle positions and rates of change.

Below please find some baseline carb setup data for BK.
My numbers should be within a thou. of actual, used high precision QB pins to mic holes.
Not super impressed with casting quality and machining, a bit of minor flash here and there on some of the ports and channels.  If you happen to read this Drew, might still take you up on sending to you for review, just playing myself for now, I like to roll my own as much as I can.

Thanks and here are my numbers:

List number        Set came from Carl's Ford
C3AF-9510-BK List 2804 and C3AF-9510-BJ List 2805
Type            2x4 4160's

Primary   
Float            non-metallic, side hung
Booster            .142 Straight leg
Pump nozzle          shipped 0.025, 0.032 now
Pump type and cam      Don't recall as shipped, White #1 now
Idle air bleed         .067
High speed bleed      .034
Metering block#         Nor sure on this, casting id is 34R 12683B
Main Jet         60
Power valve         6.5
PVCR            .032
Emulsion         2 @ .027+ in each airwell
2 @ .027 in upper dogleg (1 in each) feeding emulsion tubes
Kill Bleed         Not sure
Idle Feed restriction      .027 in idle well
Needle and seat         .097
Venturi size         1.20"
Throttle plate size      1.50"

Secondary 
Metering plate marked as 34R 9716B #6 stamped in it
Mechanical or Vacuum?      VS
Spring color         Don't recall shipped, lightest now
Diaphragm length      1.95" (to rod pin hole center)
Float            non-metallic, side hung
Booster            .142 Straight leg
Pump Nozzle         na
Pump type and cam      na
Idle air bleed         .027
High speed bleed      .032
Metering block/plate#      #6?
Idle Feed Restriction      .030
Jet size or Main restriction   .065
Needle and seat         .097

[Drew Pojedinec]

Cool, you used my form. Makes it easier to go line by line. My comments will be in parentheses.

Thanks and here are my numbers:

List number        Set came from Carl's Ford
C3AF-9510-BK List 2804 and C3AF-9510-BJ List 2805
Type            2x4 4160's

Primary   
Float            non-metallic, side hung
Booster            .142 Straight leg
Pump nozzle          shipped 0.025, 0.032 now. (This is fine)
Pump type and cam      Don't recall as shipped, White #1 now
Idle air bleed         .067
High speed bleed      .034 (I use .032 but this shouldnt be too crazy, being larger does put a larger blast or air into the main well which encourages low throttle position booster flow that is sloppy. Aka the rich at part throttle/ lean later. I generally run .031 max)
Metering block#         Nor sure on this, casting id is 34R 12683B
Main Jet         60 (main jet of 60 is pretty small for a 600, 66 is more normal)
Power valve         6.5
PVCR            .032 (small pvcr as well. Makes me wonder if they really are smaller than originals)
Emulsion         2 @ .027+ in each airwell
2 @ .027 in upper dogleg (1 in each) feeding emulsion tubes (do these have emulsion tubes?  Would be nice to know what kind they used. See originally the bk/bj and other carbs of the era used ones with four .026 holes all level just barely at float level. The only emulsion tubes now are 1970’s and later emissions carb stuff. These have waaaay more holes lower which does a fine job of frothing the heck out of the main well.  I typically dip the tubes in solder to make the old type)
Kill Bleed         Not sure
Idle Feed restriction      .027 in idle well
Needle and seat         .097
Venturi size         1.20"
Throttle plate size      1.50"

Secondary 
Metering plate marked as 34R 9716B #6 stamped in it
Mechanical or Vacuum?      VS
Spring color         Don't recall shipped, lightest now
Diaphragm length      1.95" (to rod pin hole center)
Float            non-metallic, side hung
Booster            .142 Straight leg
Pump Nozzle         na
Pump type and cam      na
Idle air bleed         .027 (typically this Iab and hsab numbers are switched,still no major red flag)
High speed bleed      .032
Metering block/plate#      #6?
Idle Feed Restriction      .030 (again very small as well as the jet. I’m gonna wager these only flow 525)
Jet size or Main restriction   .065
Needle and seat         .097

No huge red flags in the calibration. My main concern is that you are running offset spacers on that edelbrock intake while running the carbs facing forward. If you are running 1:1 I could see that being alright, but with the spacers that makes for a long circuitous route to the back cylinders.

Next tip is to hide the transfer slot under the primary plates and see how it runs.

[gt350hr]

  I agree with Drew , the offset spacers ( though a necessary item for the Eddy manifold) are causing your issue especially since they are facing forward. "I" believe you would see a difference with the carbs facing backwards and the "primary" carb in the front position. This would cause the least flow disruption IMHO helping the idle issues . I will also say what you are experiencing is not unique to the Eddy manifold. FEs commonly have a rich idle situation. Just My Personal Experience of over 50 years of "tinkering".

[427LX]

Did those carbs come with a 60 Main jet? Seems on the lean side for a 600 cfm sized carb even in a dual quad setup.
Do you have an A/F gauge to use during your road test? You WILL need one.

[Drew Pojedinec]

No they came with 66’s.

I’ve seen two types of Carl’s reproductions it seems. I haven’t check the calibration of one.
One looks like the standard 600 and one has the smooth Venturi like an 1849. An 1849 would run a 60-62 jet so that seems reasonable.

[Thumperbird]

Came with 60 mains, both carbs.  I have read where people state they are actually 550's?
Main carb primary transition slot was a little over exposed as removed, all others not visible.
I had messed with second carb and secondaries to expose slots slightly but always had too much idle but it did seem to smooth out a bit.

Pulled passenger side plugs, front 2 pretty dark gray/blackish, 3rd back medium brown/tan, back somewhere in between/medium brown.  Lots of idle and low speed operation before shutting down for the winter though.

Here are some images of the spacer/carb geometry from the intakes view.
I don't consider it that out of line, rear carb is primary and facing forward, that puts the main primaries fairly close to intake centerline.  I see it as sort of a hybrid with a tunnel ram aspect if you will.  The longer run prior to the 90 degree bends should jam air fairly well I would think and the spacer walls slope towards the center line if you will.  What I don't like is the 2 small air cleaners inside my scoop, going to bump size 1" taller to maximize area and might chop the horns, want all the fresh air supply I can get yet retain the bug catcher.  Main carb in the back is a drawback in this aspect.