Carter BBD for 318 - vacuum port identification on clone "Super 6" carb

MoPar~Man

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I'm getting happier about how this carb is working on my 318, cold start performance is pretty much tuned up but I still need to work on getting better early choke pull-off. This is a china clone of I think the Super-6 carb, which I think came out in '77. I might get more / better answers from FABO on the following questions, and I get that, but for what it's worth:

dromodary-bbd..jpg


Even when I look at all sorts of diagrams, parts diagrams for the Carter BBD's, those diagrams never show the carb from the back-side, and hence they never ID these back-side ports. I have most of them plugged, like 7, 3 and 8.

1 goes to the PCV. 5 goes to the distributor advance. 6 comes off the top of the air horn "tin hat" and it's open but there's really no vacuum from it, I think it's for the charcoal evap canister.

Now my current question concerns port 4, which comes off the throttle body and for which there is no equivalent on the 2 or 3 actual late-60's early-70's Carter BBD's that I have. I've been using port 4 to measure manifold vacuum to help tune the mixture screw and set timing. I can easily get 18 inches, sometimes 20 inches at idle. But otherwise I plug port 4. But today while the engine was idling I removed the plug and the RPM's went up a little. And that's what I'm wondering about. Is this port 4 supposed to be open? The underside of my air cleaner housing does have a nipple for a small hose, I seem to recall that a small line once was connected to it from the carb. There's also port 8, which I'm wondering about what it's for.

Another question. For those that might know about the Carter "Super 6", were those ever put on 318's back in the day? Did Carter ever come up with a "Super 8" BBD for the 318?

If in the late 70's / early 80's the slant-six's were getting the Super 6 carb, what were 318's getting?
 
As you might know, the "Super 6" was an upgraded-performance Slant 6, which included the BBD. Seems like it was the 1.44" throttle bore 318 size?

The S6 had more emissions controls than YOUR 318 has. EGR, Evap Emissions, and other similar things the later engines had on them. Many of those would have required ported vac ports, I suspect.

When I go through and finesse-tune the choke mechanism, I first make sure the basic choke thermostat is set to specs. Then I check the choke pull-off specs, too.

I will also see where on the fast idle cam the fast idle speed screw hits. I like to have my chokes come off as soon as possible. For my cars, that generally mean in 45* F weather, it starts quickly on fast idle. Then after that fast idle speed stabilizes, I'll touch the accel pedal to reduce the fast idle speed, and back out of the driveway. Then proceed to the end of the block, slow down, then turn and proceed to the next stop sign 1/2 block away. When I get to the next stop sign, about 3 blocks away, the engine is at base idle speed.

As to the fast idle cam phasing, I set the lowest step on the cam to just move the fast idle speed screw, probably about 1/4 turn from the base idle speed.

As to the choke pull-off adjustment . . . the big "V" in the linkage is there for this adjustment. A wide blade screwdriver is just right to widen the "V" slightly as a pair or pliers can close it up a bit, too. If the engine seems a bit "wanting to die when put into gear", a bit more choke closing might fix that, but not much. Tweaking with finesse is the desire, rather than larger changes.

As to "lean choke mixtures", NGK V-Power spark plugs' electrode design will be more prone to fire a leaner mixture than other electrode styles will. With the spark being motivated to happen at the edge of the ground electrode (which is also cut-back from the center electrode), more of the spark is exposed to the air/fuel mixture. Their fine-wire Iridiums would be the best is this respect.

What this means is that with a learner choke mixture, if the engine wants to falter when put in gear for the first time, a pat of the accel pedal for a bit of pump shot to cover the initial leanness of the mixture will get the rpm back so you can proceed on.

This is a HUGE "cut and try" method situation! Starting with factory specs, then tweaking to get the choke function minimized a bit so the engine is at normal base idle sooner. When it works well, it is neat! Of course, multi-weight motor oil (especially synthetic motor oil) will help things along in the cooler climates.

PCV gets full manifold vac, the larger hose. Choke pull-off gets full manifold vac. Distributor gets ported manifold vac (according to factory instructions). Any air cleaner snorkel vac motors get full manifold vac to the snorkel temp sensor, which then sends it to the snorkel motor as appropriate. Anything else should be capped with a rubber vac port plug.

As to choke thermostat specs, at about 65* F, the choke plate should just close (not a hard close, but a gentle one) by itself when the throttle is opened to let the automatic choke do its thing. If the thermostat in the divorced choke is stronger than this, adjust the coil one notch leaner to let the close be soft rather than hard.

In another forum years ago, it was revealed that the OEM choke thermostats will tighten with age. So setting them to factory specs, when aged many decades, can lead to the choke coming off slower in current times. Loosening the lock nut and setting them 1-2 notches leaner than the orig OEM spec can do the trick, usually. Only going just far enough to get that gentle/barely closed at 65* F. Again, cut and try is needed.

NOW, as to the 65* F temperature, that is AMBIENT temperatures for the air around the engine, but ALSO the metal temp of the engine and its components. Which means it might take several days to tweak before things happen as desired!

Have fun!
CBODY67
 
Although you have identified much and more description has been added, following it a listing of function by port number in your pictures:

1. Manifold vacuum: Connect to PCV valve; alternatively connect to brake booster if not otherwise connected to manifold fitting. Okay to plug if not used.
2. Metered vacuum: Connect to choke pull-off as shown in picture.
3. Manifold vacuum: Connect to brake booster if not otherwise connected to manifold fitting; alternatively connect to PCV valve. Okay to plug if not used.
4. Vacuum for EGR or Air Pump, or for the heated air inlet: Connect to ported EGR system if used; or connect to air pump diverter valve if used; alternatively, connect to the air temperature sensor in the air cleaner on 1970 and later air cleaners, if used; or can be used for a manifold vacuum source. Okay to plug if not used.
5. Ported vacuum: Connect to distributor vacuum advance unit, or OSAC valve if used.
6. Fuel bowl Vent: Connect to the crankcase breather if using the 3-port breather; or connect to the charcoal canister if used; otherwise left open, but advisable to add a screen cover. Do not plug.
7. Vapor canister purge port: Connect to charcoal canister if using one, except for 1972 style canister. Okay to plug if not used. NOTE: The port in the picture looks larger than the OEM 1/4" fitting.
8. Venturi sense port: Connect to EGR vacuum amplifier if used. Okay to plug if not used.

NOTE: The foregoing port assignments based on OEM function, which vary to some extent over the years. This aftermarket copy of the Carter BBD 1-1/4 looks be semi-universal in application coverage and to match the assignments listed, but might differ some internally. Also, other ports such as Idle Enrichment are not visible in the picture, but may not be present.

The Carter BBD 1-1/4 two barrel carburetor was used from 1955 until 1984 on Chrysler product cars and trucks with 318 engines and 1964-1969 273 engines. Although export market six cylinder engines started using a Carter BBD 1-1/4 in 1967, the American market use of the BBD 1-1/4 debuted in 1977 on the 225 Slant Six, "Super Six". The Super Six two barrel was essentially the 318 BBD 1-1/4 adjusted for use on the 225 with a two barrel manifold. The BBD 1-1/4 was used in American cars with the 225 through 1979, and on Canadian cars through 1983, and on Dodge trucks through 1983.

Following is a description for the "new" 225 two barrel carburetor from the 1977 Service Highlights:
PXL_20250206_035619052.jpg


A useful manual in addition to the factory service manuals(s):
PXL_20250206_035635923.jpg
 
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Hey @Vaanth thanks for the info. I guess I would like to figure out if this clone bbd carb that I bought off e-bay (as shown in the first post) was copied from the 318 or slant-6 designs. I guess I can measure the venturi diameter and the thickness of the front wall. Here's a look at the carb with the air horn removed:

2146.jpg


One thing I noticed is that port #4 (copper or brass tube) that I normally had capped, if I uncap it, engine RPM goes up. I wonder if it has anything to do with the idle by-pass passage mentioned here (note that this passage is not present on my carb - maybe that's what that port #4 is for?)

idle-bypass-assist.JPG
 
Hey @Vaanth thanks for the info. I guess I would like to figure out if this clone bbd carb that I bought off e-bay (as shown in the first post) was copied from the 318 or slant-6 designs. I guess I can measure the venturi diameter and the thickness of the front wall. Here's a look at the carb with the air horn removed:

View attachment 705163

One thing I noticed is that port #4 (copper or brass tube) that I normally had capped, if I uncap it, engine RPM goes up. I wonder if it has anything to do with the idle by-pass passage mentioned here (note that this passage is not present on my carb - maybe that's what that port #4 is for?)

View attachment 705164

Measuring the venturi and/or the wall thickness (comparing to a 318 version) should reveal which it may be patterned after. However, it appears that this carburetor has been crafted for a broad coverage of applications, hence there is a blend of features. I have not seen one in person to compare things to real Carter BBD 1-1/4 carburetors. I also have done very little with a BBD in a while. I do a little more with Therm-Quads. I can't see the top, but it does look like a basic copy of a 1974 and later solid fuel type, but has the external vent used in 1971-1973 rather than internal venting implemented in 1974. The base shows the notches connecting the plenum opening to the groove indicating a 1977 and later carburetor. The dual ~3/8" ports on the back for full manifold vacuum point to a ~1979 and later version. There might be more features blended.

The idle bypass assist, as described in the text in that photo, does allow fuller closure of the throttle plates, reducing air flow in the venturi, but keeping the same total flow that appears below the throttle plates. This reduces or eliminates nozzle drip. The fact that your casting has the notch shows a version late enough to be capable of bypass it if was machined. If machined, the air bypass is done internally from the area above and to the side of the venturi with filtered air to beneath the throttle plates, bypassing the venturi area.

The number 4 port is not involved as a replacement for the unmachined idle bypass assist feature. That port is a source of full manifold vacuum. Uncapping it does allow more air flow to the engine, leading to an idle increase (to a point). It is essentially a vacuum leak to unfiltered air if uncapped and not connected to something that uses it such as the uses detailed in my list. Looking at the bottom of the carburetor, that port fitting is connected to the nearby hole opening in the grooved area.
 
Here's a couple more pics of the carb. One thing I'd like to solve - is a pretty loud whisle when I set the idle down to where I'd like it to be (so I have to back it up a little to stop the whistle). I've got this idea that drilling a small hole in the throttle plate might be able to help with that?

carb-5.jpg


carb-6.jpg


I got this off Amazon in October 2023, $76 USD. The exact Amazon listing was written as "Dromedary Carburetor Carb For Dodge Chrysler 318 Engine Carter BBD Lowtop 2 Barrel V8 5.2L MB-172-HCY (Manual Choke)"

From what I read, the BBD came as either 1.25 or 1.5 inch throttle bore. The 3 old BBD's I have, and this clone, all measure 1 7/16 bore.
 
The whistle might be air passing the throttle plates as the space between the plate and bore narrows with lowering the idle. In that case, drilling a hole in the plates could alleviate the whistle. Start with a 1/16" hole. Prior to that try lightly flexing the plates either by twisting the throttle linkage by hand, or pressing on the upper edges of a plate with a wood dowel. If that alters the whistle, the hole should be used, or lightly breaking the sharp edge of the plate near the wall with a stone or sand paper. It could be air passing over any of the areas in the bore/venturi area though including bleeds, etc.

The BBD was available as BBD 1-1/4, and BBD 1-1/2. The BBD 1-1/4 was used on the 273, 318 and 225. The BBD 1-1/2 was used on the 361 and 383.

The 1-1/4 and 1-1/2 designation are the S.A.E. naming convention for carburetor flange sizes.
- The "1-1/4 inch" flange size carburetor generally has a 1-7/16 inch bore. Also known as size 2.
- The "1-1/2 inch" flange size carburetor generally has a 1-11/16 inch bore. Also known as size 3.

Also, for some more information about the Super Six BBD, and how it compares to the 318 BBD, See '76 November Reference Book: Two Barrels for Six Cylinders.
 
Did the 1-1/4 and 1-1/2 BBD (the 2 different BBD's, size 2 and 3) have the same manifold mounting hole pattern / dimensions? Did they have similar external appearance?

Even if it required some machining / drilling etc, was it ever "a thing" to install the 1-1/2 inch size-3 BBD on a 318?

Were 2-bbl Carter BBD's ever used on the small block 340 and 360? I guess I'm wondering what other 2-bbl carb with higher CFM will bolt to my current 2-BBL 318 intake manifold.
 
Did the 1-1/4 and 1-1/2 BBD (the 2 different BBD's, size 2 and 3) have the same manifold mounting hole pattern / dimensions? Did they have similar external appearance?

The BBD 1-1/2 flange is larger than the BBD 1-1/4, and the bolt pattern/size is different.

BBD 1-1/4 on the left, BBD 1-1/2 on the right:
PXL_20250207_171856686.jpg


BBD 1-1/2, rear view and front view:
PXL_20250207_173156671.jpg


BBD 1-1/4 on the left, BBD 1-1/2 on the right:
PXL_20250207_173235311.jpg


BBD 1-1/2 on the left, BBD 1-1/4 on the right:
PXL_20250207_173709231.jpg


Even if it required some machining / drilling etc, was it ever "a thing" to install the 1-1/2 inch size-3 BBD on a 318?
I've heard people mention wanting to do it and I may have seen an adapter in the late 70s, but it was not made by the "regular" adapter companies, Cal Custom, CP Products, Mr. Gasket, and probably not Trans-Dapt. I never looked into it myself. One of the Holley 2300 to Rochester 2GC/BBD adapters might be modified to do it.

BBD 1-1/4 compared to Holley 2300:
PXL_20250207_171905438.jpg


Were 2-bbl Carter BBD's ever used on the small block 340 and 360?
360 two barrel carburetors were Holley 2210 and 2245. These are the same base flange bolt pattern as the BBD 1-1/2 which can bolt onto a 360. Similarly for the 400 two barrel engines.

Holley 2210:
PXL_20250207_183155916.jpg


The only two barrel carburetors on the 340 engines were Holley 2300 and three of these were mounted on the Six Pak/Six Barrel engines. All other 340s were four barrel, Carter AVS in 1968-1970, and Thermo-Quad 1971-1973.

One of my 340 Six Paks:
PXL_20210420_171942914.jpg

PXL_20210418_185827054.jpg


I guess I'm wondering what other 2-bbl carb with higher CFM will bolt to my current 2-BBL 318 intake manifold.
Carburetors with the same flange pattern as the BBD 1-1/4 include the Holley 2280 used on later 318s, the Stromberg WW used on 318 Poly engines and others, and the Rochester 2GC small bore, which is typically a GM carburetor but was factory equipped on 1971 318s. There may be others. None these listed will flow much if any more than the BBD and the BBD is effectively better. The Aisan staged two barrel used on some Toyotas is a similar bolt pattern, but with smaller throttle bores.

A Holley 2300 to Rochester 2GC small bore adapter will allow mounting a 2300 series, Autolite/Motorcraft 2100, or similar two barrels. This involves linkage and other changes and adapters are not really a good idea. To run the larger factory BBD or Holley two barrel, swapping to a 360 intake and carburetor with related linkages, etc. is better. There will be a port mismatch, but it's of no real consequence. Swapping to a factory style four barrel setup will yield better results in general.

Stromberg WW (left rear), Holley 2280 (right rear), BBD 1-1/4 (front), (I don't have a Rochester 2GC to show):
PXL_20250207_173529474.jpg


Three BBD 1-1/4 - 1970 and earlier (left rear), 1971-1973 (right rear), 1974-~1980 (front):
PXL_20250207_173551030.jpg
 
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