Stevenola

No, in response to the caps tending to be loose on the 123

Bend the cap springs inward to increase the arch, this will tighten them up and hold the cap on better.

Vacuum leak?

What kind of carb? If it is leaning out at that rpm under light load it could also be the idle jet running out of gas before the mains take over and you have a lean gap between the 2 circuits. So either get your mains in sooner (larger main or smaller air corrector or smaller choke-depends on severity of change required) or a larger idle jet. What AFR does it idle at and WOT at?

Mine are not noisy at all and I am coming from a modern set of Michelins - no difference. Great in the rain too (unfortunately found this out also). Mine arrived in 3 days from Longstone. Oh, and they're awesome to look at

there were 2 on ebay germany recently, try a saved search and be patient.

I've used a single barrel for vacuum on my 123 and it shows no ill effects of any pulsing. Rumor has it that it has a smoothing software built in. I also have an anti-pulse valve just for this reason, but it didn't seem to matter to the 123 but perhaps get one if you're concerned: https://www.dellorto.co.uk/shop/vw-carburettor-kits-parts/vw-aircooled-manifolds-linkages-parts/other-parts-vw-aircooled-manifolds-linkages-parts/anti-pulse-valve-vacuum/ Otherwise, see for yourself and hook up a single runner and watch the 123 software vacuum display to see any unusual behavior. I wouldn't use an array of check valves for multiple ports linking as this seems awkward, and I wouldn't link the ports together from each carb (I tried this also) as it can mess up your mixture by pulling from an adjacent cylinder.

spray some starting fluid down the throat, if it fires up, it's the carb most likely.

I'm visiting Vermont and there is a beautiful Agave 02 on the same lake, anyone here? Has a distinctive name on the license plate. Lovely car, would like to see it up close if you're around this weekend.

Ask Longstone for a tracking number tonight and they will liely have it to you when you wake up.

Those are going to look insane on your car and you won't be able to stop looking at them. I haven't in the 3 weeks I've had them on. Given the approachability price-wise of these tires, we may see a trend towards original rim size, we've forgotton how cool they look. Not to mention the smooth ride with the extra sidewall.

make a set of base gaskets from material from local autoparts store. Trace the pattern on the manifold then trim out the shape and insides.

Wow this is frustrating to read, i feel your pain as i went through the same hellish path. Here's what i would do: -lose the soft mounts in favor of regular base gaskets from Pierce. This will eliminate the leak potential from these which are notorious. You can always go back to them later if you need to but for now go straight gasket. -confirm valve adjustment. What you may be seeing is reversion forcing fuel back out the throats. Confirm exhaust gaskets arent leaking too. -your carbs sound lean at idle in the video, what does your afr meter say? Remember, webers won't idle well untill warmed up, you will have to hold down the accel pedal to keep the engine from dying until they warm up. Mine will die until a few minutes have passed. Once you do the above we can jet and synch correctly, no sense trying unless your gaskets, valves, and ignition are confirmed stable as fiddling with the mix screws, air bypass scews, and throttle position is moot until this is done. I have never seen the synchronmeter affect idle speed like that so you must have a massive leak there, i suspect the soft mounts!

When I got mine there were 2 sources: Longstone in the UK, and Lucas Classic in USA. It was significantly cheaper from Longstone and they arrived in 3 days. @John S - yes, the bulldog won't do anything without a bribe

I just did 1800 miles on mine, and 4 hours in torrential rain on the highway leaving the Vintage. They felt great. And I think the Cinturatos look amazing on these era cars. I previously ran 15" Alpina replicas and Michelin tires.