C9AF-9510-U couple of questions

[Riderjeff]

I think I scored last weekend on this C9AF-U carb.  It's been in storage for 30 years, PO rebuilt it then put it in a plastic bag in the basement.
He drilled a couple of holes in the primary butterflies way back when, claimed it was the "hot ticket" when you had a "lumpy" cam to make it idle without screwing up the idle settings (!).  Anyway, I assume those are available and can be pretty easily replaced.  I have a local carb guy I plan on taking it to, have an ethanol-friendly kit put into it and return it to the factory settings

So, question 1:  66 primary and 79 secondary jets, right?

question 2: This will go on top of a Streetmaster where the exhaust crossover is NOT blocked off.  I thought I could use the standard T-Bird spacer and just not hook up the coolant pre-heat to give it some insulation and level the carb out. (Application is a '65 bird.)

TIA,
Jeff

FWIW, paid $250 but had to drive 150 miles both ways to get it!

[GerryP]

If you are going to run this carb on an open plenum intake, you will have to jet it up.  I don't know what stock jetting is for that carb, but what you're writing seems a little small on the primary.  I know the secondary uses a power valve and that secondary jetting seems about right.  But, again, it's going to be too small with an open plenum intake.

[Riderjeff]

The stock spacer is 4-hole, would that make any difference with the Streetmaster open plenum?

[Gregwill16]

That is the correct factory size jets.

[BruceS]

Jeff, I would also consult Drew Pojedenic who is on this forum and Air Fuel Spark on FB.  He would likely have the original Holley calibration to refer to. 

[Falcon67]

Agree - talk to Drew.  In my Holley experience, that back jetting is for a carb without a rear power valve.  You'd typically see a bump in jetting of 8-10 numbers to cover for the removal of a power valve.  Jet numbers for carbs with dual power valves tend to stay closer together. Used to be a common racer thing because people only cared about WOT but IMHO mostly gave you hassles with fouled plugs because you spend a lot of time not at WOT, even at a drag strip.  Only race carb I have that is missing a power valve is the methanol unit. 

[gt350hr]

   That is a nice "early" ( 1st week of Oct '69)carb. As Greg will said , yes that is stock jetting . You will "probably need to go to  69 pri and 82 secondary on the Streetmaster intake. I suggest you "try" the carb as is ( with the drilled butterflies) this allows the butterflies to be closed more and helps the idle circuit function better. If the idle speed won't go low enough "then" I would change them out.

[rockhouse66]

Just expanding on Randy's observation, an early dated "U" carb like yours has the Cobra Jet correct numbers stamped on the metering blocks.  Later "U" carbs had that number plus the 4609 number stamped on the blocks (two different numbers on each block).  The CJ numbers are desirable and make your carb more valuable than a later dated "U" carb.

[Drew Pojedinec]

Yes 66/79.
No there is no secondary power valve.
yes, 66 primary is stock, but remember you have massive high signal bell boosters from a dumptruck in there.

Yes, with the intake choice, jet 68-69.

Biggest issue with CJ carbs is the idle feed is very lean and idle circuit short.  The bellboosters start early and a small high speed bleed helps it start even sooner, so little idle to speak of.
Idle airbleed is typically .079 and idle feed is .029
This works fine for a stock CJ or any engine that makes 18in at idle.  If a large cam is used, drilling holes isn't the solution, opening up idle feed to .033 is.

yes the plates are available new, they are #172 for both primary and secondary.
One oddity of CJ carbs in general is by their very nature of how the throttle shaft/plates set up, you will expose more transfer slot than normal.  This is part of why the idle feed can be set so lean.  Part of this is the plane in which the throttle shafts are machined, and the thin plates.
A trick to look out for, the secondary plates are 172 and very very thin, this makes setup critical so you don't have an exposed secondary transfer slot.

I like to use the short vs diaphragm with these or often the secondaries will not fully open.

Personally?  for a daily driver, these are exceptional carbs as is.  You can certainly feel more low throttle torque with the bell boosters.

[Riderjeff]

Thanks for the information and advice everyone.  Sounds like some minor changes and careful setup will be all it needs. I still need to plug the engine in, so it will be a while before I can report back.

[thatdarncat]

The gang has you covered in the carb info, so I’ll just make a cautionary comment on the factory carb spacer. Many of the original Ford carb spacers of that era ( including the ‘65 T-Bird ) typically have an extended area at the back where the vacuum port is, and that extended potion is open at the bottom. On the factory application it seals against a matching pad on the cast iron intake manifold, but the Streetmaster intake doesn’t have that extra matching pad on the back to seal that style carb spacer. Unfortunately I can’t take a picture at the moment to illustrate this, hopefully I have it described well enough you get the idea. To use that factory spacer on that intake you have to be sure and seal up that area under the spacer, or you will have a massive vacuum leak, even if you have the port plugged, or hooked up as original. That might seem obvious, and you might have already planned for that, so forgive me if you did, but I’ve seen a lot of people have that issue when they swapped intakes and just overlooked it. The original cast iron FE intakes over the years had a combination of both having a matching pad to seal those spacers, or not having the pad, it just depended on what type of spacer Ford intended to use for the original application, so the issue bites the occasional person even when swapping cast iron intakes. Just a heads up.

[gt350hr]

 Great advice. The spacer deal has bit more than one person!

[rockhouse66]

Drew
I thought you had to expose the tip of the transfer slot in the secondaries to bring them into play at idle?  No?

[Falcon67]

Great advice. The spacer deal has bit more than one person!

Thats a fact!  I have a few Moroso 4 hole spacers with the undersides epoxy filled because of similar issues on aftermarket intakes.  Eyeball your intake/spacer/carb stack and look for mismatch.

[Riderjeff]

OMG!  I totally missed the spacer/manifold mismatch! Big shout out to Kevin for pointing this out.  Back to the drawing board..

I think to get the necessary carb pad angle I'll need to use a '66 Thunderbird (angled) phenolic spacer, with a short aluminum spacer underneath for the PCV port.  Don't like using extra gaskets/sealing but I am looking for some heat insulation as well as a PCV port, which the Holley doesn't have.