First off, I absolutely agree with your assessment. Now let me tell you a story:
I have a Weber 32/36 DGV, base specs with the only change being the idle jets (60 and 55). 1-1/2 turns in, 1-1/2 turns out on the Mixture, idles at 850 and drives well with my main quip being how slow first gear is, but its first gear.
Zero on Ported Vacuum. Beyond the exhaust having some hunting, it's a happy albeit slightly loud car.
This Weber is an original, built in Spain with all the original tags. From the 60's and one of the two that came with the engines my Alpines had. When I changed the head gasket, I had ordered a rebuild kit and figured why not just clean it, rebuild it and install it. The other developed a nasty crack in it and I'm working with a welder to try and save it.
And then we come to the Redline Weber 32/36 DGV 5A. Base specs from Redline on the Alpine. 1-1/2 in, 2 turns out and it sits steady at 5 inches on the vacuum gauge for the motor to run ok but absolutely inefficient. This is the one that choke made run better, that would occasionally cough from the Carb, etc. I figured it's the jets, let me change the idle jets one size and drive. It ran worse and stalled. No problem, I thought, tuning just means spending lots of time and lots of driving to get the condition right, no problem.
Each time I changed something, a jet, a twist of the screws, whatever, I wrote down the specs on a separate line on a sheet of lined paper to keep track. Each time, richer or leaner, the car would run oddly, and I could never, ever, get the idle speed to ported vacuum at zero without the screw being 1/2 a turn in to all the way out. The best I could get, with the motor absolutely hating life, is 1" ported vacuum with the car running at 500-600 RPM and it would drive. This became an experiment that I bought several jet kits for and went through in a process of 3-6 months. I finally decided to just rebuild the original Weber I had and the problems went away. So, is there a problem with the current base design?
And for the sake of full disclosure, I have been chasing a vacuum leak for a long while and ended up sanding the intake manifold on a wood block and painting the gaskets with blue Hylomar, which happened after swapping the Webers, but even with the slight leak ( now rectified ), the car ran infinitely better with the old Carb and the only issue I had was an occasional 100 RPM surge that annoyed me.
I recently read on other forums about the Vacuum Unit while reading up and learning more about timing and distributors and other things and was interested if this was snake oil or something that had been researched and developed by folks. I found this site, who is probably the supplier of these Vacuum Units to Moss:
https://www.britishvacuumunit.com/our-products.html
For the situation I went through it made perfect sense. But the fact that folks have ran this Carb on the log manifold for decades and ran fine for the most part, didn't. Thus the question I posted.
So the idea that the problem is the Carb is bang-on. Tuning can mean a lot of things and I would think each type of Carb installed on a manifold would offer its own unique set of tuning issues. I am absolutely the farthest thing of an expert and trying to acquire some Weber guru chops, but as a control in a experiment, this Redline Weber (genuine, ordered directly from Redline) was one that I hadn't messed with but had these very problems that this Vacuum Unit is advertised as a solution for.
And since I'm sure quite a few of us are running them on a Lucas 25D, I figured this would be a good discussion. As for Moss, I get the feeling they look down on us as second-class citizens and just throw things on their site with little regard in general if you don't own a 'more popular' marque.
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