with restrictor

Those are some great scans and pictures matv91, thanks for posting!

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Casually looking for a Clifford hyperpak intake for cheap.

with out

Interesting! Removing it sounds like a winner, any suggestions on how I might facilitate removal without tearing something up?

Holy great pictures! Thank you so much. I had noticed that restrictor, I see that it's south of the idle transfer slot. Would that restriction potentially cause my drivability problems? Comparing my oe carb to the 7989, the oe is missing that restriction, though the idle mixture screw on oe is capped. Wonder if it was removed, or if the factory omitted it since there is no option for idle mixture adjustment.

well on the contrary, there IS option for idle adjustment on the original carb.... it's just capped with a steel or lead plug in about the same location as your replacement carb....
has a small head that can be set with an allen, once plug is drilled (carefully) out. there was on the orig carb that came off of my 85 D150 anyway (biggest difference between yours and mine, is mine is an auto trans.)
not that it means anything if you are intent on ditching Lean Burn...... which is far and away the BEST place for the LB....
Take it out, set it under the truck and drive over the old computer.

Right, I knew the screw was in there, Did yours have the restrictor? Since the original carb doesnt have a curb idle setting, thats why I'm moving on to an older pre electric dashpot carb. Running the computer over sounds like a wise move, I'll likely do just that when I swap frames in the spring, as my poor rear bumper is bolted to the bed and ratchet strapped due to frame rot.

Back to the matter at hand, I drilled out the restriction, re-installed the carb, and can now set the idle mixture where its so rich at idle it'll make your eyes water. That being said, I set the timing to 12.5° as that seems to be best performance without detonation, and my lean surge is still there, though not as pronounced. I set the curb idle to 750, and interestingly after driving 2 miles down the freeway I came to a stop off the exit, and found my idle at 500rpms. Evidentially, something is getting warm and sealing, and if I had to take a guess I'd say it's probably the throttle shaft.

Out of frustration, I earlier ordered a reman carb for a light duty 79 D100 (autoline c7500) earlier from RA overnight. If nothing else, this carb should come with good bushings for the throttle plate, as thats one of the things they state they inspect/repair. I'm going to install the replacement out of the box The person I bought this ebay carb from had minimal info listed with it, and it was so clean it didn't look like it had ever been installed, which makes me wonder if the throttle shaft situation is why this one was shelved.

I will report back with my findings, but please feel free to add or make any suggestions in the meantime. This is my winter vehicle, and I need it back running right this week if possible.

the curb idle thing was least of my concerns.... a piece of bent up flat stock and tapped for a #10-32 and that would have gotten me past that issue.
the lack of a proper vac advance fitting and sloppy throttle shaft bushings was the bigger issue.

Also fair points, heh. I considered breaking the dashpot open and using the threaded part for the adjustment screw and putting just a long screw to contact the throttle linkage from there.

The Restriction is about .040 so slowly work your way up

What am I looking at here? Pardon my ignorance

Just for Diagnostic and testing purposes, a few strands of wire down the idle air bleed opening, will make the off idle circuit richer. wrap excess wire around the air cleaner support bracket. If the surge goes away that would suggest a problem in the idle circuit. No change that would suggest it's in the main circuit. Reset curb idle mixture after you do this

Looking at the cutaway image from the manual you posted earlier, do I stick the wire through the idle tube, or down the well towards the transfer slot?