'73 240z flat top carbs dilemma

[Dadsun]

Thanks for the honest feedback. The build date appears to be 10/72. 

So, next question is, do I wait it out for the Ztherapy round tops? (They are saying August at earliest) or pick up some at places like this:

ZCarDepot

Or new/used on eBay? Where are the best bets to source them?

 

 

[Captain Obvious]

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.     Haha!!

[Dadsun]

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. 

[Mark Maras]

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.

[Zup]

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.

 

 

 

[7tooZ]

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

[Dadsun]

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. 

[Zup]

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.

 

[Dadsun]

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 May 10, 2020 by Dadsun

[Zup]

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 May 11, 2020 by Zup

[Zup]

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.

[Dadsun]

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.