Since the #6 Diaphragm (and #3 control valve) has been removed on your car the #13 screw does nothing. The zip tie is just to keep the bar the #6 diaphragm and #13 screw attach to from flopping around since it no longer is used to slightly hold the throttle open during deceleration.

Here's an alternative view on the function of the missing screw (#13). Its purpose is to adjust/manage the effect of the servo (#6). The servo is an emissions control device to slow the rate of deceleration of the carbs when the accelerator pedal is suddenly lifted and avoid a dump of raw fuel into the intake. That's why the decals on the air filter say "don't touch". With the servo deleted from the balance tube, this screw either missing or present makes no difference. The zip tie on the linkage can be left in place or removed, same answer - no difference.

I noticed the effect of this servo very soon after taking delivery of my car back in '71 - the car was not providing any engine braking when I lifted off the accelerator. This was really a PITA to someone active in the local autocross scene! It didn't take a lot of investigation to trace the culprit and perform a bit of "civil disobedience" with an adjustment to the offending screw. Tailpipe emissions tests of that era did not detect the change and the car was more responsive to spirited driving.

Ok, this is good stuff. So, #10 for air flow balancing. In going back and forth between that other article and the service manual I have, the same terms are not always used for each adjusting screw/nut.

Btw, I do have a screw to put in the vacant hole ... From my flat top linkage "junk pile".

The screw will do nothing without the other components. I would just leave it zip tied.

7 minutes ago, w3wilkes said:

The screw will do nothing without the other components. I would just leave it zip tied.

True, but the screw will draw less attention  than the zip tie on close examination and look more OE.

Edited January 19, 20214 yr by jfa.series1

But without a zip-tie, that linkage piece will still be in there flopping around and buzzing with engine RPM. Even if there is a screw in it.

Does someone have a picture of the carburetor linkage on a Euro or other non-USA 240Z? Is that piece of the linkage not there?

Here is a pic of a non emissions set up It looks like that pice is not in the linkage.

 

Here is another pic that looks like the piece is there but no screw hole.

21 hours ago, w3wilkes said:

Does someone have a picture of the carburetor linkage on a Euro or other non-USA 240Z?

Here some pic's of my 240z euro version carbs. for as far i know..

 

The black damper was a non orig. part (orig was a little bigger.. and passified sink.)

Interesting. I don't think we ever got that damper device in the US. We got the throttle opener system instead. And the linkages are clearly different between the two systems.

I wonder which worked better.