Carburetor Conundrum (260Z)

[DadAndLadZ]

Just now, Captain Obvious said:

I'm thinking it was a misinterpretation of the procedures. Something like maybe you read "loosen the linkage between the two carbs" and your interpretation was to loosen those two nuts?  If that's the case, then it was a misinterpretation, and you should get those tightened back up.

That was exactly my interpretation. What other linkage connects them, or what is the appropriate way to loosen said linkage?

[Captain Obvious]

18 hours ago, DadAndLadZ said:

That was exactly my interpretation. What other linkage connects them, or what is the appropriate way to loosen said linkage?

Haha!! Figured. And don't feel bad about it. If you have no experience with those carbs, you just have no experience. So when they said to loosen the linkage, the intent is "Make sure the center linkage is not actuating either of the two carburetors."

Or put another way... "Loosen enough of the adjustment screws to make sure the linkage is not holding the carbs open at all."

So in the interest of teaching a man to fish... You currently have four adjustment screws. The original system had five, but because of the previous carb conversion that has been done to the car, one of the five original screws does not exist. The one that does not exist is the "fast idle adjustment". Don't get worked up about the non-existence of that screw as I believe it's only function is to temporarily raise the engine speed while checking carb sync. Once the carbs are synced, you loosen that screw and it does nothing until the next time you want to check the carbs.

So the remaining four screws... Two of them are idle speed screws (labeled in my pic above) and then there are two others.

The front screw of the two others - You will notice that since you removed that front top spring, the piece that screw is attached to is loose and flopping around. The reason for that is it originally connected to a piece of emissions equipment which has been removed from your car. That screw and the floppy linkage piece it threads into now do nothing. Forget about it. Many people zip-tie it to the linkage between the two carbs so it isn't in there flopping around, but even that is not necessary.

Then the fourth screw - The one on the center linkage towards the rear. That one is your sync screw. AFTER you get your car idling properly, you use that screw (in conjunction with the fast idle screw) to make sure the carbs are sycned ABOVE idle.

KInda hard to describe some of this with just words. If you want, I can add some more annotations to the pics.

[DadAndLadZ]

1 minute ago, Captain Obvious said:

Then the fourth screw - The one on the center linkage towards the rear. That one is your sync screw. AFTER you get your car idling properly, you use that screw (in conjunction with the fast idle screw) to make sure the carbs are sycned ABOVE idle.

KInda hard to describe some of this with just words. If you want, I can add some more annotations to the pics.

Thanks for clarifying, I finally figured out the layout of those four screws, but not until after I had jacked them all up lol…

I have owned numerous motorcycles with twin carbs, and had little trouble adjusting or even rebuilding them, but the only other car I ever had with them was my old ‘68 Mercedes 220, which had dual Solexes. Strangely they always worked perfectly and I never touched them once in the couple years I had the car.

From everything I read, these SUs are an improvement over the original carbs that came on this car, and I am sure once I figure out what’s up here, they will serve us well. I truly appreciate the kindness and patience of you folks in this forum. It’s easy to be disheartened, but you are making me feel less stupid. lol 

 

 

[Captain Obvious]

So getting back to the current issue at hand of your idle being high even with the adjustment screws being turned out.

Another remnant of your previous carb conversion is the (vertical) linkage rod that pushes down on the center linkage... That rod used on your original carbs (flat tops) is a different length than the rod used for your current round tops. Most people replace the original longer rod with a correct one, but it appears your previous owner modified your original rod instead. Looks like he cut one end off and attached a loop to the top. "Welded" maybe? 

In any event, it looks like from your pics that linkage is already slack, but just to make double dog sure, you can pop the plastic ball off the linkage at the bottom. That way the center linkage between the two carbs should be guaranteed to be loose and not affected by anything else upstream.

Here's a pic of what I'm talking about. You should be able to use a small screwdriver and pop the plastic female end off the male ball:

[Captain Obvious]

6 minutes ago, DadAndLadZ said:

From everything I read, these SUs are an improvement over the original carbs that came on this car

Well then you haven't read many of the things I've written.  Haha!! 

But regardless, it's clearly an experience issue here, not ability. You'll get it!    

[Patcon]

There are a number of members here who are fans of the flat top carbs. Captain Obvious being one of them, but we don't hold that against him! 🤣

The flat tops are tremendously more complicated than the SUs you have. You'll get it sorted...

[Captain Obvious]

Haha!! I've heard is said that it's one of my many endearing flaws.   

[DadAndLadZ]

Still banging my head against the wall. It’s 105 out today and a pleasant 92 in the garage with the AC going so I give up for the day. Here is some action video for you to peruse should you choose to go down the path of madness with me… 

[SteveJ]

16 minutes ago, DadAndLadZ said:

Still banging my head against the wall. It’s 105 out today and a pleasant 92 in the garage with the AC going so I give up for the day. Here is some action video for you to peruse should you choose to go down the path of madness with me… 

IMG_6405.MOV

I can't download the MOV file. There's something wrong. Can you upload it to YouTube?

[DadAndLadZ]

4 minutes ago, SteveJ said:

I can't download the MOV file. There's something wrong. Can you upload it to YouTube?

Here ya go, shoulda done that in the first place, sorry. 
 

 

[SteveJ]

What type oil did you use in the dashpots? Is the oil staying in the dashpots?

[240Znomad]

In my experience, with the idle adjust screws completely unscrewed the engine should barely if not even idle(ie. the throttle plates are basically fully closed and there isn't enough air/fuel mixture to run the engine).  It seems to me that that front carburetor is letting a ton of air (and fuel) into the engine which suggest that the throttle plate at the back of the front carb has a problem (bent, wrong part, installed incorrectly, who knows) or that something in the linkage is holding the throttle partially open (bent part, incorrect installation).  I think I'd start by removing that front carb and checking the throttle plate to make sure it's installed correctly and closing fully.   It's easy to take off, just remove the choke cable, fuel line, and 4 screws that hold it to the intake manifold.  If that looks ok, I'd start looking at the throttle linkage.  You should be able to remove the dashpot on the front carb and with a flashlight and maybe small mirror you could make sure that the throttle plate on the front carb is closing completely in the "no throttle" position.