round top conversion linkage geometry

[Zsomething]

I finally got the round top su's on this evening. I've plugged all the hoses to the extra stuff on the balance tube, for now. The pieces are intact. The egr is still present and hooked up. But since I removed its vacuum source, I don't think it will be opened.

I turned the key and it started running. It is popping gas out the carburetors a bit. But, I think this is expected for being completely unbalanced? So, I am feeling good and the rpm's start to rise to 4,000 with choke and 3,000 without. So, I attempted to adjust the ilde screw. It didn't seem to have an effect -- all the way in or all the way out.

Looking a little closer, I realized that the tab that should oppose the idle screw is about 1/4" away from the carburetor body with the screw all the way out!

The throttle linkage that goes from the balance tube to the carburetors is the same length. But, the angle between the ball joint to the pad appears to be something like 10 deg. difference (just guessing).

So, it looks like I will have to adjust the screw on the firewall linkage. Hopefully, I have enough extra room to make it work.

Are there any other places that I will be able to add slop? Should I try those first?

[beandip]

I would like to help but I can't figure out what you are talking about. If you could take a picture this would help greatly. Gary

[Zsomething]

I would like to help but I can't figure out what you are talking about. If you could take a picture this would help greatly. Gary

I'll see if I can get a picture tonight.

After thinking about it a bit. I think the problem is basically that the round top su setup had thick spacers, and the angle on linkage between "the ball shaft" and "the opener" was appropriate for the bigger spacers. But, the small spacers moved the carburetors closer.

Basically, the carburetors moved closer with the smaller spacers. So, the throttle linkage is no longer correct.

Anyway, a picture is worth a thousand words (or a million of my words). So, I'll get those up.

[Zsomething]

Basically, the problem was that I was using the short linkage from the round tops (second picture). The shorter linkage had two problems. First, it allowed too much axial movement. Second, it did not allow the existing maintenance screw to be used (fourth picture). Third, it did not allow the carburetor to return to full close, because the angle is incorrect.

The third problem was unacceptable. So, I fixed it by combining the round top lower linkage (which matches the carburetors) with the flat top upper linkage (which matches the balance tube). After doing this, I adjusted the threaded rod on the firewall to be the correct length with no slop, and now all three problems are fixed.

The first picture is the flat top carburetor linkage, which does not fit the round top carburetors. The third picture is an axial picture of the flat top linkage. The angle between the ball end and the screw that pushes the carburetor butterfly open appears to be greater than the linkage for the round top carburetors. The fifth picture is the round top linkage that is on the car now.

[Exdamyankee]

I had the same problem when I switched from flats to roundtops. You need to use the thick spacers from the old roundtop setup, it won't line up right with the flattop spacers.

[Zs-ondabrain]

I don't know exactly what comes with a Z-THERAPY kit but I know that they charge about $600 for just 2 carbs and linkage.

I am selling these. they are 4 screw S.U.'s that I've completely bebuilt. They have been torn down and rebuilt using only the BEST parts I had. ANything that was not complete clean with the original plating was bead blasted and clearcoated using 500 degree clear coat. Everything else was cleaned, inspected, readjusted, or replaced.

All new studs, washers and nuts on the intake manifolds, which were cleaned and glass bead basted. I also polished a few things that needed it. Everything was set back to OEM specs, like the floats and needle placement. New gaskets on the floats, filters were cleaned inspected and replaced if needed.

This complete intake and SU set-uip with linkage is FOR SALE I'm asking $450 plus $25 for shipping (2-3 day Priority Mail thru USPS) with insurance and tracking. for a total of $475 out the door.

First come, first serve. I've spent a good 40 hours rebuilding and assembling them and we ALL know that they (in this good of condition) are worth A LOT more than the asking price. They WILL need to be adjusted upon installing them onto your motor. the mixture nuts are set at 2 turns out and the throttle and ballance screws will need to be adjusted accordingly. There is NO egr Valve and a new one should be purchased and installed before start-up. There is no water lines connecting the 2 intakes. There IS the 2 water line nuts and line fittings, that go on the outer edges of the intakes.

Those are only needed in cold climates for heating up the carbs and are usually bypassed by most 240Z owners. 4 screw SU's don't have the coolant resevoir to accept coolant like the 3-screws do. The intakes are E88 and the ballance tube is an E46. I will include a heat sheild for $25 more if needed.

If you are interested in the set. Please contact me at wolfin32z@yahoo.com

Sorry to Jack this thread but it seemed apropriate because of the photos below, which may come in handy when looking for info on the linkage set-up.

Dave.

[Zs-ondabrain]

I put it in the classified section.

http://www.classiczcars.com/classifieds/showproduct.php?product=2122

As is for $450

Heatsheild is additional $25

Shipping Via USPS priority Mail (2-3 Day) $25

Thanks for looking,

Dave

[Zsomething]

I had the same problem when I switched from flats to roundtops. You need to use the thick spacers from the old roundtop setup, it won't line up right with the flattop spacers.

I tried to avoid using the thick spacers because I heard that they don't allow the proper flat washer-lock washer-nut, although I did not try it. I am sure that lots of people have had this exact problem. But, I didn't find much info on it searching. So, hopefully the next person will find the two solutions: use thick spacers, or experiment with a combination linkage setup.

This complete intake and SU set-uip with linkage is FOR SALE I'm asking $450 plus $25 for shipping (2-3 day Priority Mail thru USPS) with insurance and tracking. for a total of $475 out the door.

Sounds like a pretty good deal to me.

[Tony D]

This is a common problem with people who do this conversion, or if you use DOUBLE spacers (and 75mm threaded studs to compensate for the extra length of double spacers) for more mid range torque with the SU's.

What the common fix for these situations entails is either finding the correct linkage for the setup you have, or to take the linkage that goes from the pedal to the first bellcrank---it has a threaded end on it. You can cut it to 'close enough' length, and then make final adjustment with the threaded ball end, and lock it down.

What is dangerous on both these conversions is that you DO have the possibility of making up a linkage that is too short (what it sounds like you have)---with a longer shaft it may still be too short, and if the linkage goes over-center you will LOCK the carburettor throttle shafts at about 1/2 throttle---BAD NEWS!

Make sure your linkage is LONG ENOUGH and CAN NOT be pushed over-center to lock the linkage open. This is why I suggest the threaded solution---you can get it just right, and keep all the slop out of the linkages by having two adjustable links in the system.

I have been running the double-insulators on my car for close to 7 years now, and it works flawlessly!

Oh yeah, and you do have to be careful with putting on the lockwashers and nuts...if you use jam nuts it's easier, but you can still do it with the standard nuts and lockwashers if you put it together a piece at a time, and start all the nuts together, and tighten them down evenly. You have to remove them the same way.

Good Luck with the project.

[Exdamyankee]

I tried to avoid using the thick spacers because I heard that they don't allow the proper flat washer-lock washer-nut, although I did not try it. I am sure that lots of people have had this exact problem. But, I didn't find much info on it searching. So, hopefully the next person will find the two solutions: use thick spacers, or experiment with a combination linkage setup.

Yes, you need to use the longer studs as well. And I was a dumbazz for not figuring that out until after I already had the carbs on. Had a bear of a time pulling the studs from the old manifold, there were a couple that would just not let go. So, I went down to the local Screwz-R-Us and found a bin with the correct length studs. All is well now, I'm pleased to report!

[Zs-ondabrain]

I think they are 8mm 1.25 studs X 45 or 50mm long

I just bought new studs for the intake I just built, pictured above.

Dave