28 minutes ago, Captain Obvious said:

Yeah, I'm measuring including the rounded top portion. Essentially I'm interested in "how far does the valve stick out of the bowl lid", and that includes more than just the hex portion.

So I'm measuring everything from the sealing washer surface to the top of the valve (not including the movable internal bits). Like this:

 

So this is my (cracked body) 72F valve. I get .806 (20.5mm), That makes sense since the TSB mentioned earlier says they lowered the bowl level for the 72 front carb by 2mm. Both the valve and the bowl lid ears got 2mm longer for the 72F, so all the numbers line up to support that:

So when your eyes get back into focus, let me know.   

.806" Exactly what I have. I'll get a picture in a couple of cups.

28 minutes ago, Captain Obvious said:

Oh, and it's clear to me that Datsun really messed around with stuff in 72. The float valves are unique, the lids are unique, everything is different than the previous years. It looks to me like they were chasing minutia. Some engineer realized the slight geometry differences between front and back carb bowls when they mounted on the car and convinced management he could make it better. I'm thinking they should have just left well enough alone.

Also makes it clear why I was having a hard time getting these carbs right... They're all kinds of wrong inside from previous owners.    

The thing for me was the newer valves you get today are the same length, front and rear. They said to use the washers to make up the difference. I never could get it right so I took the rear off another set and now have two rear lids. I went back to "they should have just left well enough alone".

Also I think the DVD shows how to set the height using the Grose valve but you can't do that with the newer style "needle valves". I wish they would add a sheet of paper in the rebuild kit explaing that. It took me a year to figure it out.

Edited April 18, 20213 yr by siteunseen

Well I guess I'm going to test that statement about the new aftermarket valves being the same front and rear. I just put in an order on rockauto for rebuild kits for the 72. They call out two different part numbers for the kits and make it clear there is a different one for front and rear. So I'm going to soon see why they spec different kits for 72 F and R.

If it's not the needle valve length, then I don't know what it's gonna be. I guess I'll let you know in a little while when the kits get here! 

I got the ones that were the same lengths from ztherapy. They're on the car with 2 rear lids, short arms.

Here's the OE front. Looks to be a little more than .806? Could be an eyelash fell on there.

Edited April 18, 20213 yr by siteunseen

7 minutes ago, Captain Obvious said:

Well I guess I'm going to test that statement about the new aftermarket valves being the same front and rear. I just put in an order on rockauto for rebuild kits for the 72. They call out two different part numbers for the kits and make it clear there is a different one for front and rear. So I'm going to soon see why they spec different kits for 72 F and R.

If it's not the needle valve length, then I don't know what it's gonna be. I guess I'll let you know in a little while when the kits get here! 

Here's some aftermarket needle type.

 

 

@Terrapin Z, @siteunseen

When you guys get a chance, could I trouble you both to take a caliper measurement of the short valve going all the way to the top of the valve?

Also, do your short valves have the "R" stamped on them? Looks that way in the pics, but just checking.

59 minutes ago, Captain Obvious said:

 

@Terrapin Z, @siteunseen

When you guys get a chance, could I trouble you both to take a caliper measurement of the short valve going all the way to the top of the valve?

Also, do your short valves have the "R" stamped on them? Looks that way in the pics, but just checking.

👌

@Captain Obvious I hope this is what your after. 

Terp, Awesome. Thanks for the great pics. And your number matches the Hitachi valves I have here.

So assuming site's 72R valve comes in at the same dimension as what's in your pic, here's a summary of what I have so far. Most of this is old news, but just to put it into a form that my little brain understands...

The float valve for the 72F should be 20.5mm. That is 2mm longer than the previous years and Datsun adjusted both the length of the float ears and the depth of the valve recess of the 72F lid to accommodate that change. The intent seems to be "They wanted the front carb float level to be approx 2mm lower than it used to be in previous years."

The float valve for the 72R should be 18.5mm, and it's interesting to note that this is the same length valve Datsun used on the previous round tops in 70 and 71, but a different part number*. And again, Datsun adjusted both the lengths of the float ears of the 72 R lid as well as the depth of the valve recess to change the float level. The intent seems to be "They wanted the rear carb float level to be approx 2mm higher than it used to be".

*An interesting side conversation would be... So if the float valve for 72R was the same length as the previous years, why did Datsun bother to change the part number? Why not just spec the 70-71 valve for use in the 72R lid? I've got two theories about that:

First is that there's a note in the EF section of the 72 FSM about how they changed from a hardened steel tip to a rubber tip for the sealing of the float valve. Second is that I've got (what I believe are) early 70 valves here and they have a different through hole. The 70 valves I have 2.0mm through hole, while the later 72 valves have a 1.7mm through hole.

So while the length may be the same, they may have sprung for a new part number because of those changes. However, despite those changes, it seems to me you could use the same valve for the 70-71 round tops and the 72R. The 72F is still the outlier.

Here's mine.

These Grose valves let way more air pass through. They have a small hole on each side. 6 in all. I can't wait to try them out.

 

7 hours ago, siteunseen said:

Here's mine.

18.5mm and has an "R" on it.  Perfect. You guys are the best!!  @siteunseen  @Terrapin Z

My rebuild kits should be here in a couple days. I sure hope one of them is the long version. I really don't want to have to carve a new one myself.