I’ve been working on the tune most of the weekend.
Here’s where I’m at.
Idle 12.5:1 AFR
Light accel 12 – 11:1 AFR
Hard accel 9.5 – 10:1 AFR
Cruise at 35 mph 15:1 AFR
Anything over 45mph starts going lean. 17+:1 AFR

Looking like fuel starvation at this point. I installed a new fuel filter today which seemed to help. Tomorrow I will test it with an electric fuel pump and see what happens. I hooked up a fuel pressure gauge today, but it is for fuel injection and didn’t even register, though I got a good stream of fuel when I pressed the pressure release

To answer your questions-
I don’t know the origin of the carbs, but this model was stock on early Datsun 240Z’s and some other Japanese domestic & import cars (early ‘70s).
I have watched those videos several times over the past few months, they’re good, but are based on a properly configured engine/fuel set-up.
The springs have no markings so I don’t know what they are.
I have installed a set of KD needles, the Hitachi and SU’s are interchangeable. But, just to complicate matters, have a different numbering system.

I spoke to Eric/Planetman, who recommended DX needles, I graphed out the KD’s and the DX’s and both are just about overlapping in the range where I am having problems.
Yes, pulling out the choke does richen the mixture, though I didn’t have time to try it at higher speeds.

Thanks for your input.
I will make run well, it’s my ride to Davis!

-Tracy