Specs on AC,AD carbs

[jcarlson]

I have a set of 2x4 carbs C8OF-9510-AC/AD carbs. I'm looking for some info on jetting, plates, secondary springs, etc. Hoping someone here has the original specs. I looked at MustangTek website and they have them listed, but there is an error in that they say they have a power valve and these do not. I know Ford listed these as 652's for drag racing only. Holley tech has no information.

[thatdarncat]

The Holley Illustrated Parts & Spec’s Book shows those Holley List 4201 & List 4202 carbs with #70 Primary Jets, Primary metering block # 5764, Secondary metering plate # 28.

[GerryP]

The Holley Illustrated Parts & Spec’s Book shows those Holley List 4201 & List 4202 carbs with #70 Primary Jets, Primary metering block # 5764, Secondary metering plate # 28.

I was curious about this post since I had never heard of these carburetors -and that's not unique since I am familiar with only a handful of Ford Holley carbs.  I did find an old publication of a 427 build using these carburetors on a tunnel wedge.  In the story, Ford said to begin tuning with the primary jets at 77, rather than the 70.  I thought that made sense as a minimum jet for a 650cfm carb without a power valve channel running on an open plenum intake.  Here's the story:  http://wildaboutcarsonline.com/members/AardvarkPublisherAttachments/9990398697818/1968-02_HR_Ford_427_Performance_Tips_1-3.pdf

[jcarlson]

Thanks. 
Those are the specs I’m looking for. These are original carbs and I tried the 77 jets and is too rich. I’ll go down in size since they came with 70’s. I suspect the 77’s are what Ford suggested to be safe. I’m running them on a BT dual plane intake so the signal is probably stronger.
I’ll play with the secondary springs.
One day of racing left here in Buffalo !!

[Drew Pojedinec]

I’m plating right now....
7th time I’ve done a throttle shaft, for a GT40, so has to be perfect.
Lemme get to my laptop later and I’ll post the whole calibration

[Drew Pojedinec]

List number         4201/4202
Date
Type            4160
Primary
Float            Side hung brass
Booster            .160 small bellbooster
Angle Channel         .139
Pump nozzle         .031
Pump type and cam      white#1 30cc
Idle air bleed         .070
High speed bleed      .030
Metering block#         5764
Main Jet         70
Power valve         na
PVCR            na
Emulsion         2@.027
Kill Bleed         .028 emulsion tube feed
Idle Feed restriction      .033
Mixture screw hole      .064
Venturi size         1 5/16 1 3/8
Throttle plate size      1 11/16 172/173

Secondary
Mechanical or Vacuum?      VS
Spring color         Plain
Diapghram length      2.2
Float            Side hung brass
Booster            .160 Large bellbooster
Idle air bleed         .028
High speed bleed      .024
Metering block/plate#      plate #28
Angle Channel         na
Emulsion         na
Idle Feed Restriction      .040
Jet size         .075

[Drew Pojedinec]

On another note, 1 5/16, 1 3/8 venturi and 1 11/16 throttle plates are a really really awesome combo.

No you cannot replicate it by using a different baseplate on a carved up 1850, the entrance and exit angles of the venturi are different.
This is the same main body casting as BC/BD carbs but obviously different boosters.

Yes yes 70 *should* be too small. You ignore the boosters pull. A Bell provides a different signal than a straight leg, it pulls harder on the jet.
Same reason a CJ runs a 66 main jet and a 79 secondary jet

[GJCAT427]

Hey Jim, What took so long to get on this site! Haven`t heard from you in a while. I see Lancaster reopened. I think you will like this site better than the old forum. Lots of info. Garry

[427LX]

Interesting carb specs.! 

So how would these carbs compare power wise to a pair of 650 Holley carbs using the familiar 1 1/4 and 1 5/16 venturi
combo using the 1 11/16 throttle plates?
For street/strip use would not the smaller venturi give a bit better throttle response?

[Drew Pojedinec]

Not just the venturi on the AC/AD but that booster will pull fuel hard.

I cannot say “powerwise” as I lack a dyno, but most of Ford’s SK carbs had this style booster. I tend to think they did not install them to go slower.

[Drew Pojedinec]

AC/AD

IMG_1828[1] by Drew Pojedinec, on Flickr

Boosters:

IMG_1831[1] by Drew Pojedinec, on Flickr

-BD carb for reference:

IMG_1833[1] by Drew Pojedinec, on Flickr

[jcarlson]

Drew,
This is awesome stuff. Thanks.
I've always wanted these carbs and so I'm excited to play with them. I know they are probably "tuned" for the TW intake, but I'm trying them on the dual plane. The old Muscle Parts books say to use them on either intake. The bell boosters are the key for me as I have a heavy car with only 4000 stall converter. I have the pink cams and 28 squirters for longer shot of fuel off the line and it seems to be working with a best so far of a 1.52 60ft. The car leaves much harder than with the 1850's I ran previously.
The idle seems a bit rich, but maybe jetting down will help. I'm not familiar with the idle circuits on other carbs so it is hard for me to compare.
I'm going to start with the plain spring in the secondaries.
Hopefully, the weather on the 19th will give some good results!
 

[Drew Pojedinec]

Rich idle?
Close primary throttle shafts and open secondaries.
It'll let in more air and less fuel assuming that you do NOT expose the secondary transfer slot (that'd be a mistake).


Thanks for appreciating the info, I have data on almost every FE carb.  I detail a lot of it, and multicarb tuning tricks on my FB page "AirFuelSpark"

Plain spring "seems" stiff for 2x4's, but if you notice, these have a vacuum secondary amplifier tube in the venturi, so it'll have a stronger opening signal.  As with jetting, VS springs are engine dependent, go weaker till you feel it, and back up one. 

[jcarlson]

Thanks Drew,
I'll visit your FB page later today.
I'm going to jet down from the 77's and see if the car likes it.
I ran the light yellow springs in the 1850's and it seemed pretty good, although to be honest it is hard to tell unless you make big changes to these springs. It seems to affect when the secondaries pull in, not how much they open.
Of course making ignition timing changes also affects the carbs....almost too many tuning parameters!! The car likes around 40 degrees total, but it starts too hard as I have the timing locked out. So I have it set at 36 for the moment. I'm going to re-curve/unlock the Duraspark distributor before the 19th to cure that problem.

[427LX]

Great carb info and thanks for the pictures Drew! 
Now that BD carb pictured...They used the extended secondary squirter setup along with the vacuum secondary action??
Thought those were a mechanical secondary like the Holley 4224.