The port under the fuel inlet/fuel bowl is like the EGR vacc. port and the Vapor canister purge port... The ESA/spark control vacc. source is off the side of the carb in the middle (on 1978 carbs it's pointing the same way as the bowl vent tube), aka. same side as the vaccuum assist for the choke pulloff...


Reroute and lets see if that helps a little (I know I helped a guy a long time back that had this same problem, his car would drive very well when 'HOT', but be gutless when cold...checked the manual and he used the EGR port for spark advance...sheesh).

-D.Idiot

All good advice, but electrical issues are not causing the low vacuum readings or the idle speed misbehaviour.
Really close: Step-up rods.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan. I need those kinds of memory jogs. After sleeping on this post I awoke suspecting the carb is the real isue, but as my Grandad used to say, it isn;t what you don;t know that hurts you, it's what you know for sure. What he was saying was, don;t assume anything. So those checks are not a bad idea.

So with that said, I think since the problems showed up with the carb change, it is likely carb related. Simplest fix will be if using the correct port for vacuum advance fixes things. Let's hope. Some other carb issues are float height, and condition of needle and seat. You might be running a little high on the resevoir fill height, which throws all of the calibrations off in your carb. You really need a manual on how to adjust this carb for your vehicle. The adjustment on the step up rods is very important, and easy to do, but I cannot remember how it is done. It's one of those things where you loosen a screw, perform another step, and then retighten the screw.

Does your model have a removable inspection plate on the top of the carb right in front of the air horn? Not all BBD's had this adjustment, but if yours has the inspection plate over top of them, then yours is adjustable and will need to be set up properly. Maybe Dan or DI can point us towards an instruction sheet on line. But I think we will need a carb number to get the correct instructions. Did your new or rebuilt carb come with an instruction sheet? It seems to me maybe it should have. It has been a long time since I bought a carb, but I can recall a sheet being in new carb boxes that had specs for each adjustments for each application.

Sam

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Don't have a sheet (singular), but how 'bout this 40-page PDF I just put together:

http://u225.torque.net/cars/SL6/docs/BBD_Manuals.pdf

It consists of Carter's operation and service manual for the 1¼" BBD (which covers all variants used on all makes) plus a Chrysler publication covering adjustments and differences between 6-cylinder and V8 BBDs. Both manuals are very adamant that the step-up rod adjustments not be touched. There is an interesting altitude-compensation adjustment mentioned on page 9 (right below the warning about the step-up rod adjustment) and page 22. This is a new one on me...I've never gone looking for that adjustment. Wonder how many cases of improper idle and screwy driveability have been caused by improper adjustment of the altitude compensator...?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

But if you rebuild the carb, you take those rods out, and you have to put them back correctly somehow. So I think this admonition is intended to keep neophytes from fouling things up. I know that in a rebuild sheet they tell you how to adjust them correctly, and I think I remember them being a little different for different applications. I think I remember that they are set to their final height after the idle speed and throttle blade adjustments are set.

There is a plastic cam under the cover that is rotated on a shaft actuated by a link from the throttle shaft. This cam has a screw that fastens it to it's shaft. The hole in the cam that the screw goes through is slotted, so the rods sit in the jets at a height that is somewhat variable, spending on where the screw is in the slot when it is tightened. As the throttle blades are opened, and the shaft rotates, the metering rods are lifted slightly. Since the rods are tapered, the mixture will depend upon where the screw is tightened in the slot. I think there is a step down in the rod about half way down that allows even more fuel through the jet when the blades open to a certain specified amount.

When I ran a BBD I played with that adjustment all the time, and could change the mixture in effect without changing the jets or the rods. I thought it was pretty trick. I thought it was great feature of the BBD.

Of course you know carburetor is French for "don;t mess with this".
So maybe we should take up cross word puzzles. I guess I would be worse at that anyway. So I will stick to "messing with this", no matter what "this" is on a car.
Sam

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Mmm...being as how the admonitions were both directed at professional, trained mechanics, I don't agree with you on this point.
I don't remember seeing adjustment instructions for the step-up rods in the "TechLit®" instruction sheets that ship with carb kits for BBDs, but I could be wrong. I'll have a look; we've spent a lot of time lately cleaning up my stockroom, so I know where the carb kits are now!
And French is a language composed of 26 letters, of which 118 are silent! Actually, carburetors work on the FM principle (that stands for "Magic").

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Too many people who were born on third base actually believe they've hit a triple.

The 1978 FSM has an adjustment called [ Qualifying Step-Up piston ] that the 1976 and 1977 do not mention.

Thank you MatvV91. I guess that is the version I had. I liked it. I think that is the conversion I sold to Newpopop (Chris) when I went EFI. It was a junk yard item when I bought it, and I paid little attention to what car it came off of. I am pretty sure it was a Volare, but I never learned the spotting features of the Volares and Aspens.

Sam

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Well I moved the vacuum hose that comes from the distributor to the port on the passenger side of the carb. I didn't get a change at all in idling. I'm going to pull the distributor in a couple days and get the timing closer to 10 or so to see if it idles better.