Jump to content
Dadsun

'73 240z flat top carbs dilemma

Recommended Posts

Yeah, that's early alright! I bet those are the original carbs that came on that 240. Even if you do change to something different, keep those in a box on a shelf somewhere.

If it were me, I'd pick up a set of cheap round tops and do the refurb work to them myself. But I've been into them before and I ain't skeered. If you got the money and want someone else to stand behind the work, then ZT seem to be the go-to guys.

One thing to remember... If you decide to go with round tops, you'll also need the linkage bits that connect the front carb to the back carb. The round tops are narrower than the flat-tops and your original flat-top linkage will be too short.

But in all honesty, I'd pick up a pair of later generation flat tops and go down with the ship.   :victorious:  Haha!!

  • Like 2

Share this post


Link to post
Share on other sites

There look to be several options for buying round tops out there, ranging from bad shape/need attention, to the ZTherapy ones. 

Several on eBay in the $325-600 range, but I don't have the experience yet to wade through those, so I may go the ZTherapy route, if I can wait that long. 

Btw, the original owner had this in a box of stuff. Anyone used one of these to tune a flat top successfully? Something tells me I'm going to run into several vac leaks in the process, and now I'm considering replacing with some MSA headers. My head is swimming. 

IMG_20200509_160617.jpg

Share this post


Link to post
Share on other sites

A Uni-Syn is a great tool for balancing SUs. I still have my 47 year old original one that I bought for my first adventure in tuning SUs. It still works great.

  • Like 1

Share this post


Link to post
Share on other sites

Hi Dadsun--

Mark is right. You will need the Uni-syn  as an aid to balance the airflow in your carbs regardless of flat top or round top.

I wouldn't be spending money on a header until I found a true need for it. The header is immaterial to vacuum leaks. It might help with engine compartment temperatures, but until you've driven the Z hard enough and long enough to reach those temperatures how do you know it needs that as a remedy?

The real issue with servicing the flat tops in any meaningful way lies in the fact you must completely remove them from the car to open them up, replace gaskets and adjust the internal floats and fuel nozzles. That involves dis-assembling a lot of air and water connections just to get to the point of faithfully adhering to the Factory Service Manual step by step so that the required adjustments are made . No shortcuts. No kidding.

Once you go through this process the flat tops are reliable and perform very well for extended periods of time with no issues. I've driven my flat top powered Z round trip from NW Arkansas to Austin, TX in 2017 and Atlanta, GA. in 2018 with no problems. I couldn't be happier with them, really like that they are original to the model year and take some pride that they are rarely seen in proper operating condition.

 

 

 

  • Thanks 1

Share this post


Link to post
Share on other sites
15 hours ago, 7tooZ said:

I would not buy carbs on eBay or any other Unknown source

Anyone had experience with these ZStore round tops? Link.  Less expensive than ZTherapy and probably could get them much sooner. 

Share this post


Link to post
Share on other sites

Unless something has changed, the ZStore gets their carbs from ZTherapy, so you may as well deal with ZT directly.

Many times the ZStore lists items as available when they really aren't and you place an order and are subjected to long wait times for fulfillment.

Don't order until you call them first and they confirm all your questions.

 

  • Like 1

Share this post


Link to post
Share on other sites
Posted (edited)

I'll contact the ZStore and see what's the scoop. 

In the meantime, I ordered the $40 flat top rebuild kit, also. It does not come with the needles or floats. Those would add about $50 per carb. In your experience, should I go ahead and order those too?

And, yes, I've got two parallel tracks going here. :-) I figure spending another $100-200 for the sake of possibly salvaging the flat tops and building my confidence to tune them is a worthy near-term investment. 

Edited by Dadsun

Share this post


Link to post
Share on other sites

Posted (edited)

The ZStore probably won't have the correct floats or the right needles for your flat tops. There are no immediate sources for them.

Chances are that your floats are good but need adjusting. More likely they just need freeing up on their pivot pins from years of varnish and gum accumulation.

If your needles have not been bent and the fuel nozzle orifices have not been rubbed out of round by them they are likely OK.(shiny areas on the needle and close inspection of the nozzle orifice under magnification will reveal this)

If and when you disassemble the flat tops, be very careful and try to not damage the rubber seal that is in the channel between the lower fuel bowl cover and the carb body. Most rebuild kits contain both types of this seal ( one for the early and one for later iterations of these carbs)  but there has been some discussion that they are not as well made in some of the kits as the originals. You may want to re-use the originals in that case, if you get them out without distorting them badly. They usually come out fairly easily if you are careful.

Edited by Zup

Share this post


Link to post
Share on other sites
3 hours ago, Dadsun said:

building my confidence to tune them

Exactly what is required------I didn't know $hit from Shinola when I ventured into them. If an Arkie  like me can do it, you and anyone else willing to put effort and time into them can be successful in bringing them back to life.

CO, Motorman7 and a few others on these forums are with me in swimming against the current.

  • Haha 1

Share this post


Link to post
Share on other sites
21 hours ago, Zup said:

Unless something has changed, the ZStore gets their carbs from ZTherapy, so you may as well deal with ZT directly.

Many times the ZStore lists items as available when they really aren't and you place an order and are subjected to long wait times for fulfillment.

Don't order until you call them first and they confirm all your questions.

 

Yep. This was precisely the case. The Z store still gets them from ZTherapy, and they are having to wait a few months right now, too. Looks like I'll have time to try my hand at tuning the flat tops.

Share this post


Link to post
Share on other sites
On 5/9/2020 at 8:06 PM, Zup said:

 

I wouldn't be spending money on a header until I found a true need for it. The header is immaterial to vacuum leaks. It might help with engine compartment temperatures, but until you've driven the Z hard enough and long enough to reach those temperatures how do you know it needs that as a remedy?

It did exhibit a little bit of dieseling after I turned it off the other day, this was after about 25 minutes of spirited driving. 

I noticed the ZStore also sells heat shields (pic) and I'm curious if those are helpful. Also, what's the purpose of an insulation block between the carb and engine?

Screenshot_20200511-152344.png

Share this post


Link to post
Share on other sites
Posted (edited)

The insulation blocks on the carbs and mechanical fuel pumps help prevent direct heat transfer from the head. The heat shield does a similar thing - a barrier between the exhaust and the carbs. If your car is relatively unmolested, you probably have a heat shield already in place.

BTW - if you ever decide to tart up your ride a bit, I have a replated fuel rail looking for a good flat tops project!

 

Rail 73 A.jpg

Rail 73 B.jpg

Edited by jfa.series1

Share this post


Link to post
Share on other sites

23 hours ago, jfa.series1 said:

The insulation blocks on the carbs and mechanical fuel pumps help prevent direct heat transfer from the head. The heat shield does a similar thing - a barrier between the exhaust and the carbs. If your car is relatively unmolested, you probably have a heat shield already in place.

BTW - if you ever decide to tart up your ride a bit, I have a replated fuel rail looking for a good flat tops project!

 

Rail 73 A.jpg

Rail 73 B.jpg

That's beautiful, JFA. If you've seen the earlier pics from under my hood, you know it needs some prettying up. I may take you up on that at some point this summer. 

No heat shield currently. See pic.

IMG_20200512_093719.jpg

Share this post


Link to post
Share on other sites
18 hours ago, Dadsun said:

IMG_20200512_093719.jpg

From this picture it looks like you already have headers and the air ports have bolts in them? If I remember correctly back in the mid 70's MSA had headers with the ports in addition to "comp" headers without the ports with a warning that they may not be legal in your state. If those are headers, are they 6 to 1 or 3 to 2 with a "Y" connector and do you have 2.5" exhaust?

As for heat shield it looks like ZCarDepot has them;

https://zcardepot.com/products/carburetor-manifold-heat-shield-stainless-240z

 

Share this post


Link to post
Share on other sites

The headers appear to be 3 to 2. And then the two remaining send through the muffler and then two stacked tailpipes. 

IMG_20200513_172020.jpg

IMG_20200513_172059.jpg

IMG_20200513_171934.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.