SU Carb Re-Plumbing Question

[ApexArbitrage]

Hi everyone!

I'm working with Dyme PSI ( https://dymepsi.com/) to replumb some of the hoses in my Datsun. This has led me to a few questions regarding the SU carb lines that I hope someone can answer.

overviewS.jpg

Brendan at Dyme sketched out how the new plumbing would look like with individual feed and return lines for each carb instead of the current loop so we can go to all standard AN fittings and eliminate the need for any rubber hoses:

diagram.jpg

(sorry for our highly technical diagram, basically pressure relief banjo bolts take in the fuel and the banjos take the return)

So my questions are -
1. What's the size and thread pitch of the current banjo bolt?
2. Does the over-engineered looking banjo at the back of the engine bay (i.e. left side in the below photo) that currently takes the return line have any special function like regulating the fuel pressure?

banjoS.jpg

3. What are the right adapters to fit onto the fuel and return tube (the hoses will be AN4 feed and AN6 return)?

lines.jpg

BONUS ROUND!
The other fitting I'm having some trouble figuring out is the breather on top of the valve cover:

breather.jpg

Is there an adapter to convert it to AN fitting?

Lots more pictures here if the above are not sufficient.

Thank you everyone!
Max

[unklpat]

You must have a pump in-line? I would replace lines as they are oriented now, unless You want a more cluttered look. Where are you going to route the PCV line to? That fitting on the valve cover has value, so it would be best to make a new plate, then adapt your AN fitting to it(90 degree threaded).I will trade you a less desirable short nipple, for that long one, then You could Tap in whatever threads you want, after cutting the nipple off. Pat

[ApexArbitrage]

Where are you going to route the PCV line to? That fitting on the valve cover has value, so it would be best to make a new plate, then adapt your AN fitting to it(90 degree threaded).

The PCV line is already routed to a catch can with an AN10 inlet and a breather filter, you can see here. No issues with that, just don't like how bulky it has to be. I don't have any tapping tools otherwise your idea of getting a new plate (I'd still want to keep my original one) sounds very clean.

[unklpat]

I'd still encourage you to keep the routing as is, It's cleaner, and factory. I think the only difficult part is the short piece between the carbs. By the way, you don't have the recall brace on your first carbs' banjo bolt. I, or anyone could make you a plate for a 90 degree fitting. If you let me know the threads you would want to screw into it, I'll make you one. I have both versions of the nipple, so I don't need yours. Pat

[ApexArbitrage]

I'd still encourage you to keep the routing as is, It's cleaner, and factory. I think the only difficult part is the short piece between the carbs.

I completely agree and, yes, that short bit was the reason for doing the more cluttered layout. I will have to think of how to keep the routing stock but still upgrade the plumbing.

By the way, you don't have the recall brace on your first carbs' banjo bolt.

Sorry for the stupid question, but what is the recall brace?

I, or anyone could make you a plate for a 90 degree fitting. If you let me know the threads you would want to screw into it, I'll make you one.

That'd be great! I'd like an AN10 thread, since my catch can has male AN10 terminals.

[unklpat]

The recall brace comes up from the front fuel bowl, 2 screws towards motor, and supports the hard line into the banjo bolt on the front carb. It is like a "t" support, keeps it from coming loose. the rear carb apparatus is for safety in case of? I don't know the story on that. I would leave it alone, if you can make the lines. I need a fitting for the valve cover, if you want a threaded replacement plate. Does anyone have one to donate? PM me for address, give me a week. Pat

[ApexArbitrage]

Pat - sent you a PM.

To keep routing stock for the fuel lines then could I use these AN to tube fittings (1/4" feed and 5/16" return) and this short hose for the connecting the two? A bit of a compromise but a lot more straightforward.

[unklpat]

Won't give an opinion, for obvious reasons. You've already bypassed the front fuel line configuration, what you have can be very clean. Hope you keep your fuel pressure low, and have an inertia cutoff switch. Pat

[JT68]

I'm just trying to make some sense of this thread, if you are trying to clean up the fuel line routing, eliminate the return and use a 67 fuel T. Way cleaner than a bunch of AN, and much more desirable in the long run.

There are lots of photos of the correct T on 311's. We have a kit for that too.

If you don't want to eliminate the tank return, you need the valve for proper function. The tank return is a good thing in very hot climates.

[ApexArbitrage]

JT - All I wanted to do was replace my old rubber hoses with high-quality ones and the owner of the company that makes the ones I wanted suggested the individual line configuration in the sketch. I thought it'd be best to talk to the experts here on the forum, hence the thread. It seems like the consensus is keep it as-is.
Not sure if you remember me calling on you last year when rebuilding the engine, but if you do then you'll recall that I basically have no idea what I'm doing and that I was very grateful for all your help!

[JT68]

Your very welcome Max. Right, I would not go with the plumbing in the sketch-if you run the return, you need the rear valve or something similar.

If you want to simplify the plumbing, run it 67 style.

[keith0alan]

On the race car we went with AN hose and fitting. The VARA tech people gave us no end of grief. What made them happy? Conventional hose and hose clamps. Most of the fuel system is AN fitting and braid covered hose but the last bit to the carbs is old school. The transition from AN to rubber hose was a problem. I ended up fabricating a fitting to do it.