carb help

[grimdame]

hi yall i was told by a friend to come here and that someone here may be able to help

ok im havening trouble mounting a carb i was giving to try out on my 61 cad, it is a Rochester 4b carb. i bought a adapter kit for it, but with the back plate on the engine the screws are not long enough to work, do i need that black plate on there? or am i supposed to replace that piece with the adapter plate?
here are some pics



also im not too good with engines, body work yes, engines no. so i have no clue what hooks up to what, is there any online manuals that would tell me?

any help would be great

[TJ Hopland]

The adapter in your top picture is called a spread bore carb to square bore manifold (most commonly Quadeajet carb on a Holley manifold).   Your manifold looks to be spread bore which should be what the quadrajet in your second picture fits on.   What is the issue?  The black plate looks to just be a straight through spacer perhaps installed to try and lower temps and prevent vapor lock.  You dont need that new adaptor.

[grimdame]

the bottom back holes on the carb are bigger then the bottom holes on the manifold, thats why i thought i needed the adaptor

[dadscad]

TJH is correct, the black plastic spacer is there as an insulator and to allow exhaust gases to circulate around the front of the carb to help with cold engine operation. The heat riser closes when cold and forces exhaust gases through the intake manifold and under the carbureter until temperatures rise enough to open the heat riser.

If the carbureter has larger rear bores and the rear throttle plates hit the black insulator, you can remove the black plastic spacer and install the Aluminum adapter in it's place. Be sure to use proper gaskets on the bottom next to the manifold so they will be suitable for the high heat of the exhaust gasses that will run in the channel in the manifold under the spacer.

Enjoy that Caddy!
David

[greg surfas-15364]

1967 was the first year that Cadillac used a Quadrajet on any of it's engines, so I believe something is amiss here.  Was that the carbeuretor that came off the engine? I think not.  A Carter "AFB" would be more likely and my guess is that all the "bolt-up" connections would then be correct.
The Bakelite insulator between the Manifold and the carbueretor is for reduction of heat transfer to the Aluminum carb.  There should be a stainless steel shim with just four, carb barrel holes placed between this insulator and the carb.  No shim, no idle.
Go back to the shop manual for your car, get the correct carb number and get that carb.
Greg

[The Tassie Devil(le)]

I hope I am not too late coming in on this one, but putting a Rochester Quadrajet Spreadbore Carburettor on a Manifold designed for the early '60's Rochester and Carter Carbies does require the Aluminium Adaptor, because of the size of the Secondary throats.

The use of a good gasket between the Manifold and the Adaptor is vital to keep the Exhaust Gasses in check as they flow across the front of the Manifold.

But, as far as the bolts not fitting, you will simply require longer ones to attach the Carby to the Manifold, through the Adaptor, as the mounting holes in both the Original Carby, and the Spreadbore are in the same location.

Bruce.

[grimdame]

ok so i bought a cater afb carb and it lines up perfectly no problem, but does anyone know where i can find some information on how to hook it up like what hoses go where?

[TJ Hopland]

I dont have any good manuals that go that far back so I cant help with the hookup.

Bruce, I assume there is a special adapter for that purpose? The one he had in the picture looked like a square to Q one which I would think would not work that well if at all.   Didnt the early 4bbls still have a fairly wide spread on the primaries, at least compared to the holley square style?

[The Tassie Devil(le)]

G'day TJH,

The Cadillac Manifolds, after the mid '50's style with the Carter WCFB's and their 4 holes the same, the Secondaries were larger than the Primaries, but not as large as the full later Spread-bores.

Before using any of these adaptors, one must check each side to ensure that the holes in the carby, and the Manifold will be satisfactorily not blocked.

In the past, I have "Massaged" adaptors to ensure that there is no compromise in air-flow, and in cases where I have done Carby Changes, I have milled out the guts of the manifolds to accept the replacement carby.

Bruce. 

[greg surfas 15634]

Okay,
Now that you have the original (type) carb.  Go back to what I said about the carburetor insulator and stainless steel shim between the insulator and the carb.  It goes, in order from bottom to top, manifold, gasket, insulator, shim, gasket, and finally carburetor.
The vacuum lines you should have would be the vacuum advance which is on the distributor and the vacuum port on the left, front of the carb.
The carb base has a large port in the rear, and the power brake booster vacuum and the transmission modulator vacuum lines go to this port, via fittings.
The intake manifold has a port behind the carburetor for auxiliary vacuum to the AC system.
This should cover all the vacuum connections.
The AFB is a very simple and highly efficient carb when jetted and adjusted correctly.  That is why Cadillac stuck with it.
Greg

[Roger Zimmermann]

Okay,
Now that you have the original (type) carb.  Go back to what I said about the carburetor insulator and stainless steel shim between the insulator and the carb.  It goes, in order from bottom to top, manifold, gasket, insulator, shim, gasket, and finally carburetor.
Greg

Greg, I believe that the shim sould be cemented at the bottom of the carb...Maybe somebody else will confirm.

Roger

[greg surfas 15634]

Cementing or using a sealing agent between the carb and the stainless steel shim was an expedient way to get around buying a second base gasket when overhauling an AFB. Most gasket kits had only one base gasket, and buying a second seemed inconvenient to some mechanics.  A second gasket is correct, cementing only leaves a mess on the shim and carb bottom when you have to rebuild the carb in the future.
That's my story and I'm sticking to it.
Greg

[Roger Zimmermann]

Cementing or using a sealing agent between the carb and the stainless steel shim was an expedient way to get around buying a second base gasket when overhauling an AFB. Most gasket kits had only one base gasket, and buying a second seemed inconvenient to some mechanics.  A second gasket is correct, cementing only leaves a mess on the shim and carb bottom when you have to rebuild the carb in the future.
That's my story and I'm sticking to it.
Greg

Your solution seems to be logical. However, it's not what the shop manual is saying. They had maybe good reasons to specify: manifold - gasket - insulator - gasket - tin plate, coat top of surface with gasket cement - carb. (from the '59 shop manual)
As you install the tin plate directly over the insulator, are you sure that there is no air leak at this point? Logically, you would need a third gasket here!

[The Tassie Devil(le)]

By the time I ever get to do any Carby Work on these Manifolds with the Exhaust Passage, the area is ALWAYS totally blocked with crud, and I therefore seal up the vertical passages, and seal them off completely, and then, if it hasn't been done already, remove the Exhaust Butterfly from the Exhaust Manifold to Engine Pipe, thus freeing up the whole Exhaust System.

One can simply remove the butterfly and leave the Counterweight in place, but solid so it looks original, and improved all-round performance.   Especially in areas where the Choke isn't that necessary.

Bruce.

PS.   The Engineers that describe the repair operations in the Workshop Manual, would be thinking that the repairers are using pristine replacement parts, and not re-used, and old parts.

[dadscad]

The 63 shop manual indicates the following sequence to install the carburetor.

Gasket on the manifold, insulator block, gasket, stainless steel shim, carter carburetor.

The shop manual states the Carter AFB used that year, I assume other years also, will not idle properly if the stainless shim is not installed directly under the carburetor. The shim is supposed to be coated with a spray on sealant.

David