Captain Obvious

Word on the street is that the tapered pipe threads used (everywhere?) on the Z's was British standard... BPT. So the 14 TPI would be correct, but the thread profile is a little different than NPT.

Haha! Maybe they wanted some scratches in there to hold oil like piston ring cross hatch marks? Seals like a little lube,

Haha! I try! So as scary looking as that integral equation is, it is basically means "average". As in "Roughness average". And to make matters simpler, I think a surface finish of Ra at 8 u-in can be achieved with something around 400 grit sandpaper*. The typical (and best) means for achieving the appropriate surface finish would be by grinding the shafts and again... A well tooled machine shop should have that capability. * Note that I did see some indication that the UK numbering system for sanding paper grit is different than the US, so be aware of that.

Hardened and polished throttle shafts paired with bearings would be best. Those bearings are designed to run against a pretty high quality surface finish. For example, the versions offered by McMaster recommend a surface finish of Ra = 8 microinches Where... That said... Even without hardening, new stainless shafts with a good polished finish will be worlds better than worn soft brass.

I'm no carb expert, but on the ones I've messed with the wear appeared to be on the shaft. the chrome plating had been worn through, and once that happens, it exposes the (even softer) brass underneath, and things spiral quickly from there. billgtp posted a pic of one of his shafts, and it might be a trick of the camera, but I think I can see the brass color peeking out at both ends. Between the bearings and the marker lines? As for availability of new, I have no idea. Certainly any well tooled machine shop could make them, but at what cost?

As a matter of fact.... Yes. There's no way I'm moving that old oil into the new motor.

Yup. That's the closed end version I was referring to. Using those on the outboard ends of the carbs would eliminate two of the four leaks:

Haha! I was serious about the intent. The joke part is the value of that mod on our (mostly stock) Z cars.

Unbelievable.

That looks reasonable. Hope that's the end of the issue!

I don't know about your side of the border, but on the US side, I'd get 'em from McMaster. Here's the through version with seals on both sides https://www.mcmaster.com/5905K586/

Hahahahaha!!!

Thinking about this a little... Most of those drawn cup needle roller bearings are available in a configuration where one side is closed off. Totally blind. If one finds that the vacuum leak past the bearings is objectionable, they could use that closed end variety on the outboard ends of the carbs. That would completely eliminate two of the four potential leak locations.

Didn't Madonna wear those?

It looks like they "thinned" the web on the original throttle shafts. You can see the underlying brass where they cut the shaft down. You know.... For higher performance because it reduces air resistance at WOT.

That is clearly not the way things are supposed to work and the first thing I would do is put the vapor tank back in. Only thing that confuses me is you said you were getting liquid in the vent line even before you took the vapor tank out? So you were getting liquid in the vent line with a stock configuration vent tank and hoses?

Neat modification. I don't think the seals on those bearings are rated for vacuum or pressure though. I think the seals are only intended to keep grease in and dust out. That said, I wonder if the ensuing leak would be any more or less than the original sleeve bearings. I'm also pretty sure the chrome plating on the shafts would not be recommended by the bearing manufacturer. And if the chrome plating has already been worn off in spots exposing the soft brass underneath (as is so common with used shafts), there's no way it would be recommended for those rollers. However, with another "that said" here... At low speeds you will see in this application, would the rollers still be better than the original sleeves running on the soft brass? I'm no bearing expert.

When you get gas, do you top off the tank to the very top or something? Just looking for theories.

Excellent. Well, not the "forget' part, but the part that it works well.

Have you made changes to the way your tank venting is done? Anything other than replacing failed / leaky hoses? I don't remember what you have done back there. And I think you are supposed to have the "check valve" device installed in the vent line running from rear to front. You're saying you don't have one?

And everything works as intended?

I don't know anything about knock sensors other than they are piezoelectric. Piezoelectric materials change shape when a voltage is applied to them, and conversely... when a piezoelectric material is subjected to a shape change, it generates a voltage. That's about all I know. Do you have any links or learning sites that do a good job of explaining more detail than that? How this pertains to knock sensors?

There should not be liquid fuel in that vent line. Wonder how that happened.

Maybe if I put it a different way? Where Does that help?