Because 'everyone' say so. For years now. Especially Z Therapy and you can understand why they say so. They even suggest you ditch the EFI in favor of their round tops.

Flat tops bad, early round tops good.

flat tops will vapor lock in outside temps above 85. Datsun recalled the 73 and 74 z and installed heat sheilding and an electric fuel pump but it didn't fix it. Here in the south I remeber many a 73 that wouldn't restart afetr they heat soaked for a few minutes.

Keep the oe parts, install the early carbs and enjoy driving the Z

I'll just repeat what I 'typoed' last year when I thought this thread was done as to why flat tops are bad.

Because 'everyone' say so.

Stephen, I'm honored you like my turn of phrase. While I did just think of that while composing that post, I would not be surprised if someone else had not thought of that earlier. Seems sort of obvious to me...:-)

It matches up well with a phrase I am always telling my students. Common sense is not all that common anymore...

Common sense is not all that common anymore...

How did you say that?Common sense mostly help us to solve some problems.

I rest my case.

JayHawk you could be creating a market for the flatops. Got me thinking I need a set - I am a fan of original setups and this is interesting.

All I have seen for years is boat anchor this, boat anchor that, regarding flat top carbs. Fed up with it. I am another fan of flat tops. I see a lot threads on specific items on the early 240z and how people look to have these. Fair enough...you want to keep the car "stock/factory". Why not these carbs, which are a larger stock item than some metal emblem (not knocking these)? They are part of the heritage of the S30. And I thought this site was all about that?

Sure, they take a bit more set up, but you are only metering two components, fuel and air (and a little bit of vaccum). A problem with worn round tops also occurs on the flat tops, worn throttle spindles. Once you understand how the flat top works, you understand correct set up, and how they work, there is no reason why they should not work. Some cars in Japan are still running '73 flat tops and have no problem, and they don't have a different carb.

Stick round top carbs on if you want an easy life, but please consider the boat anchor comments for flat top carbs from the un-informed.