Today I did a carb swap on my truck. Didn't use the super six manifold that I have,just an adaptor plate. All went well and the truck seems to run fine except for a couple of issues. 1) I can't idle the truck down any lower. I'm not sure of the rpm but by ear it seems a little high. The adjustment screw is out pretty far.
The truck also runs strong through the first three gears but from 55 mph on up it's a dog. It didn't run this way with the 1 barrel. I have it adjusted, I think. It holds a steady 21 inches with a guage on the manifold and except for a slight miss runs smooth.
The carb is a bbd and I believe for a 318. Anyone have any tips? Will this still be a problem when I put the other manifold on?

If the carb was for a 318 it will have holes in the throttle plates. This are because the V-8 needs more air when idling than a slant six. This might explain your high idle speed. See if you can locate an original Supersix carb or fill in the holes in the throttle blades. Also, since it is a V-8 carb, it is more than likely jetted incorrectly for your application. What do the plugs look like? Are they black and sooty? I don't have much experience with Carters but hopefully this will help.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

That's correct, the V8 BBDs need to be reworked (throttle plate holes closed up and resized, smaller) for slant-6 use. And those 2bbl-to-1bbl manifold adaptor plates frequently cause pretty severe driveability problems.

i dont know about other people's experiences with the bbd swap, but in my case i put the 318 bbd on and havent had any problems. i didnt change anything.

thats what i know about the deal, but if i were you, id be looking for a 2 bbl intake. i cant see how those adapter plates could be very condusive to a well running car.

A 318 BBD will not necessarily have holes in the throttle blades. The one I am using dosen't. If I remember rightly, the BBD with the holes were for a special emissions package.

The BBD I have, is pre-emissions, it only has PCV and ported spark. I picked it out of a junkyard carb pile because it was still shiny, and still had the rebuild stickers attached. To make it work properly, I had to set the float level, change the choke arm to the \6 one, adjust the needle drop and set the accelerator pump shot. Basically what you have to do with any parts store rebuild. Once that was done, the carb has worked beatifully.