260z round top conversion: a couple questions

[ConchZ]

I think you also need to consider the vacuum line for the power brake booster.  It's a preformed rubber hose and the routing is slightly different for a 73/74 than an older balance tube.   I have a 73 with round tops.  My PO kept the original intake and balance tube, but I have a really nice polished set of intakes and matching balance tube that I want to swap on there this winter.  However, I'll have to buy a different vacuum line.  

[Cooper260z]

noted. Thank you guys so much. I don’t know why this change of carburetors seemed so daunting before. Guess I just got psyched out by reading about the problems people ran into. 
 

If there’s anything you think I should know about this, I’d love to hear it!

Thanks again!

[Zup]

On ‎9‎/‎9‎/‎2020 at 10:25 PM, Cooper260z said:

But what about that blocked off thermostat port?

You are in truly GREAT hands using the Captain's explanations and advice, but I will chirp in here with some comment.

This is all dependent on a "given" that you intend to convert to round top carbs from the flat tops.

The lower thermostat housing that you have with the blocked off port is interchangeable in mounting with the earlier lower thermostat housing. The upper housing caps are the same. You could swap out the lower housing, install an earlier manifold water fitting and reduce some of the clutter and previous owner damage. When and if you decide to change over to the earlier balance tube you will also have the opportunity to change to the earlier type water piping at the rear of the engine block. This would eliminate capping off the now un-necessary water lines on the water piping used on the later flat tops in that area.

The routing of the water lines with the "Y" connection shown in your lower photo is on the wrong side of the block/ valve cover.  It should be on the opposite side ---mounted below the spark plugs. It reduces in diameter and converts to a hard metal pipe the wraps behind the engine and connects to the rubber coupling shown above the heat shield on the lower photo.

If you have on hand all of the parts shown in your photos you have most everything you need to make a complete proper conversion. I don't know if you have on hand the earlier metal water pipe that wraps around the rear of the engine.

On ‎9‎/‎8‎/‎2020 at 8:53 PM, Cooper260z said:

The l24 balance tube has one port at the end of it but that port is currently blocked off and I don’t know what would’ve been there originally, if it would’ve been water or gone to the exhaust manifold like the 260 one.

The capped port on the balance tube shown in your third photo should be plugged just like it is on the very end. Just a plug, instead of a fitting with rubber hose and a bolt. The remaining  fitting is where you obtain vacuum for your brake booster and can be left there (vertically) or moved to the end (horizontally) depending on which hose type you have coming from the brake booster. 

I did the complete round top conversion on my 73, but then later made the decision to return to the "original" flat tops with all the associated air/ water/ vacuum plumbing in going back to a "stock" configuration.

[siteunseen]

Is this the pipe @Zup?

Not sure about my position for the pic but I'm pretty sure this is the one off my '72. I deleted the coolant flow through mine so I would be willing to provide this to a good cause. I.E, if it will be used?

Cliff

Okay, walked my lazy arse downstairs and it is the pipe off a '72.

Edited September 13, 2020 by siteunseen

[Cooper260z]

@Zup I do have the other thermostat housing and early water line. The water pipe you see in the bottom picture is just an extra one that’s sitting on the engine. The guy I got the engine from just threw that in there and I don’t usually say no to free parts. That whole l24 was free. 
 

So then to change the balance tube I’d just have to figure out how to block the hole in the exhaust manifold I think. 

 

Also I’m planning on to use the heat shield from the l24 because it has the hooks for the rerun springs for the round tops which I think my current heat shield lacks 

Edited September 13, 2020 by Cooper260z

[Zup]

Right on Site!!

 

Coop----sounds like this is under your control now. Best of luck with your conversion!

[w3wilkes]

5 hours ago, Cooper260z said:

I’d just have to figure out how to block the hole in the exhaust manifold I think. 

The MSA 6 to 1 ceramic coated headers do a pretty good job of that. ?

[Cooper260z]

On 9/13/2020 at 8:51 PM, w3wilkes said:

The MSA 6 to 1 ceramic coated headers do a pretty good job of that. ?

The thought had crossed my mind. Might do

[Cooper260z]

I’ve finally started the process of taking things off to put the round tops on, and I have another question that I don’t THINK I’ve asked yet. 

What should I do with this diaphragm? Not exactly sure what it does but from what I can tell, earlier 240Zs at least don’t seem to have them so I’m guessing it isn’t necessary and I’m not sure if the aftermarket air filters I bought (but haven’t received yet) will allow for it to plug in. 
 

So really the question is do I add that port in the balance tube to the list of things to plug? And also what does that diaphragm do, just so I have that knowledge. 
 

Also what is that vacuum hose for and can I plug that? Because I’m not sure if the new air filters will have a port for that either 

[Captain Obvious]

That diaphragm device is your anti-backfire valve. The round top cars used something similar. Not located in the exact same spot, but pretty close.

As for the vacuum line, that went to your "idle compensator" device built into the air cleaner. It's job was to lean out the idle mixture a little bit when the engine got hot. The round top cars didn't have anything like that and you can just pull the hose off the balance tube and put a cap over the nipple.

[dutchzcarguy]

On 9/13/2020 at 6:10 AM, Cooper260z said:

If there’s anything you think I should know

I wanted to ad.. why all those gardenhose clamps, get yourself some good (original) clamps.  they are much better. Those are used in planes for good reason.

[Cooper260z]

thanks again!

 

@dutchzcarguy I thought the same thing! That’s how I got the car, they’re are so many I thought that they might've been Original. I change them out every time I take one off