Seeking proper choke function with the 4 screw type

[inline6]

I've started driving the 240Z which I have been restoring since 2018.  Many years ago, when I had SU's on my 12/70 240Z, the choke didn't work particularly well.  I only needed to use the choke when it was actually cold out, like temperatures under 40, let's say.  When I would operate the lever, the nozzles would drop.  That would help the engine fire up, no problem.  But, within a matter of a few seconds, the engine was "choking" on too rich a mixture, running really rough.  I would, of course, push the choke cable towards the closed position.  However, the engine would not run without me pressing the gas pedal - push the choke all the way in, it would die, leave it partially out, it would run very rough - way too rich.  

Fast forward about 30 years, and now I want to get the choke working properly on my newly restored 6/71 240Z.  Referencing the factory workshop manual:

 

"For the adjustment of the starting interlock opening, bend the connecting rod (4) as shown in Figure EF-45 with an appropriate tool such as radio pinchers to change its length."  

 

I have done this.  When I did, the carburetors idle set screws had already been set properly, and the carbs synchronized.  With the choke lever in the closed position, the lever that the connecting rod operates is not in contact with the throttle plate linkage. 

When the choke lever is pulled the connecting rod pulls on the lever, and the tab at the other end of the lever contacts the throttle plate linkage.

 

To set the clearance of the throttle plate59 to .62 mm "throttle valve" to the carburetor body "throttle chamber" to the proper specification, ".59 to .62 mm (.0232 - .0271 in)", I flattened a piece of annealed wire with a hammer and the flat portion of my vise.  I measured it with vernier calipers.  When it was the right thickness, I used it as a custom feeler gauge.  I inserted it in the carburetor port between the throttle plate and bore and adjusted the length of the connecting rod to set the gap.  Now, when I pull on the choke lever, both linkages activate and open the throttle plates from their previous open location (as set by the idle set screws for proper idle when the chokes are not operating) to the correct specification. 

During operation of the choke lever, there is a finite amount of movement of the connecting rod and lever.  As you pull the lever, there is some "dead area" where the lever moves, but where the linkage has not yet moved.  Additionally, if I recall correctly, the choke lever requires a lot of movement from fully closed... to fully open, whereupon the connecting rod and linkage has then fully operated.  To say it another way, when one pulls the choke lever to operate the choke, there is a small amount of movement where nothing in the choke linkage "has done anything", and then, as one pulls the choke lever more, the connecting rod engages the lever, and the lever engages the throttle plate linkage, causing the throttle plate to open further.  

So far, I have only been describing what happens to the connecting rod/lever/throttle plate when one operates the choke.  However, there is another part which is important in the functionality of the system: the nozzle.  As the choke lever is operated from closed to open, there is a point in that travel where the (1) "Connecting plate A engages.  When it does, it pulls the jet nozzle downward.  As explained in the workshop manual:

Here is the problem I have right now with my car.  When I pull the choke cable as far as it will go, the nozzles bind in the nozzle sleeves.  Pushing choke lever forward, to disengage the starters is not sufficient to put the nozzles fully back into the nozzle sleeve.  Instead, I have to tap on the bottoms of the nozzles with my fingers to get them to unstick and return. 

To address this problem, I am now focused on this: 

 

According to the workshop manual, that (2) stopper nut is supposed to be set so the idling adjust nuts can only be turned out 1/2 of a turn (from their operating position which is 2.2 turns down).  One half a turn, is only .5 mm!  

If that was set properly on my car, that means the nozzles would only drop .5 mm when the choke lever is pulled.  Can that be right?  

I have another question.  This is something I can't find an answer for in the factory workshop manual.  When securing the choke cables to the carburetor linkage with the set screw, do you push the choke lever as far forward as it will go?  If you do that, there is some amount of "dead space" when pulling the choke lever before anything happens at the linkage.  Does one pull the linkage up by hand until the lever contacts the throttle shaft and tighten the screw to affix the choke cable at that point instead?  If done this way, there would be little to no dead space when pulling on the lever.  Or, does one tight the screw to affix the cable when the starter linkages are fully relaxed? 

And how do you ensure that both linkages activate the same amount?

 

Edited Monday at 12:58 AM by inline6

[Captain Obvious]

Let's start with the simple... That 0.5 mm (half turn of the knob) will not limit the amount of nozzle drop when you pull the choke lever. That 0.5 mm limit is simply an attempt by the factory to prevent you from adjusting your carb nozzles four or five turns down and driving around like that. It's an emissions stop limit so you don't accidentally (or on purpose) set your nozzle operation way too rich.

The other easy question... When you pull the choke cable, there is nothing wrong with having a little dead space before the nozzle starts to drop. The last thing you want is for everything to be all cinched up tight and you're driving around with your choke on a little bit when you don't want it.

Push the lever all the way "off". Tighten the set screws. You're done. As far as balancing the choke, I've never worried about that. Seems to work just fine even if they are a tiny bit difference between the two.

[Captain Obvious]

Now, the more complicated...

2 hours ago, inline6 said:

When I pull the choke cable as far as it will go, the nozzles bind in the nozzle sleeves.  Pushing choke lever forward, to disengage the starters is not sufficient to put the nozzles fully back into the nozzle sleeve.  Instead, I have to tap on the bottoms of the nozzles with my fingers to get them to unstick and return.

The nozzles should not ever stick in the holder. If they are doing that, you need to figure out what is going on with that before you move forward.

I've seen grit in the nozzle holes. Grit in the actuating mechanism. Burrs on stuff. Varnish on stuff. Plating too thick interfering with stuff that should rotate. Plating flaking off and becoming grit. Lack of lube where necessary. Incorrect needle alignment. Incorrect assembly of the little springs...

But the point is, you need to make sure the nozzles return to full UP home when the choke cable isn't pushing them down.

And can we work on the adjustment of the throttle plate opening amount when you get the rest of the stuff under control?

[inline6]

34 minutes ago, Captain Obvious said:

Let's start with the simple... That 0.5 mm (half turn of the knob) will not limit the amount of nozzle drop when you pull the choke lever. That 0.5 mm limit is simply an attempt by the factory to prevent you from adjusting your carb nozzles four or five turns down and driving around like that. It's an emissions stop limit so you don't accidentally (or on purpose) set your nozzle operation way too rich.

Ah, yeah right.  The nozzle and the connecting plate A are the only parts that drop... not the idling mixture nut.  So the stopper is not in play.
 

26 minutes ago, Captain Obvious said:

The nozzles should not ever stick in the holder. If they are doing that, you need to figure out what is going on with that before you move forward.

The nozzles are new genuine Nissan units.  Everything was/is clean.  They only stick when they are pulled down "a long distance" by the choke cables. 

It is this distance that they drop that I keep thinking about.  I am fairly certain that they are dropping as much as an inch or more.  I have found it to be excessive - it isn't necessary to pull the choke lever fully to enrichen the mixture for starting.  

When I pull the choke lever fully, then the nozzles drop much further.  With the choke lever pulled fully, the nozzles are possibly more out of the nozzle sleeve than in at that point.  That is when they bind against the nozzle sleeve.  As soon as I touch the bottom of either nozzle, it snaps upwards (the linkage is spring loaded) returning to the normal position.  

I will try to measure the amount of movement of the nozzle when pulling the choke lever and report back. 

Edited Monday at 02:38 AM by inline6

[Patcon]

It is my understanding that the bar #1 that is connected to the bottom of the jet need to be bent to make the needles not stick. Although I am not totally certain which way to bend it to prevent binding when the choke is applied

[Captain Obvious]

10 hours ago, inline6 said:

I will try to measure the amount of movement of the nozzle when pulling the choke lever and report back. 

There is no real adjustability on the max amount that the nozzle drops. Sure, you could bend the #1 lever to potentially change it, but it will put things out of alignment and potentially bind. Maybe someone tweaked yours at some time in the past?

You should be able rotate the choke actuation lever all the way to it's stop, and when you release it, the springs involved should be enough to pull the nozzle back up. It should come back up and "snap" against the bottom of the holder nut.

I will measure the amount of nozzle drop on a carb here and we can compare notes.

[Mark Maras]

 When my nozzles started sticking in the down position, I removed the carbs and found the #1 bar warped. The ends were not parallel to their attachment points. A slight twist with two pairs of pliers on the bar realigned the ends of bar #1 with their mounting points. That ended the problem with the nozzles.

[Patcon]

I believe the idea of bending the bar (#1) originated from Ztherapy IINM

[Captain Obvious]

I measured the nozzle drop on a set of four screw carbs here and (with the nozzle nuts turned all the way up "home") I get about about 1/2 inch.

If you're really getting 1" drop on your troublesome nozzles, then there's something weird going on.

[Captain Obvious]

And by "something weird", I mean, maybe the annoyingly complicated nugget of springs and levers and stops etc. has an issue: