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

[MoPar~Man]

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:

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?

 

[CBODY67]

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