Like TonyD, I'll be happy to help you eliminate the pollution in your garage by taking the flat tops off your hands. (I really need the linkage actually..)

But Weasel, you might want to look a little deeper into the whole flat top story than the oft repeated "boat anchor" or "emission carb" claims by posters who believe that round tops are "SUs" and flat tops are not. Or who believe that only the flat tops were made by Hitachi.

I'm going to try and scan into PDF format a copy of the "mythical" and "impossible to find" 1975 Nissan 240Z and 260Z Fuel Modification Plus manual that turns out not to be very difficult to find (2 have sold on eBay in just the last couple of months). It has all of the service bulletins, fixes, and tuning information on the flat tops in one manual (that should have been in the FSM, but wasn't....)

Conventional Wisdom may be conventional, but it is not always wisdom.

--Bob

Original Owner of 1973 240Z HLS30-125678, who drank the Conventional Z Wisdom kool aid and paid a lot of money to replace the flat tops with round tops. And now regrets that....

Weasel73, First off the intake on the engine right now is a vary good intake. Leave it on and just remove the flat tops . Like all before me here save the old emissions parts. If ever you want to bring the car back to original you will need the stuff. As Escanlon said just zip lock the stuff and put it away. Find a good set of SUs , either 4 screws or 3 screws. Either will work the same. At the same time pick up a early air cleaner and heat shield. '70-'72 vintage. You will also need the thicker insulators that go between the SUs and the intake also the linkage that goes between the SUs. the flat top linkage is a different length. Gary

Thanks to everybody for the input. I think what I'll do is get the car running with the flats on it. The lady I bought it from said it ran fine when it was parked, so I plan to get the motor running before changing anything. Then I think I'll probably store the flats, and install a set of earlier rounds. I'll store everything from the flat tops (and the smog stuff), but in the end, I want to drive this car, not show it.

I want the most reliable carbs I can use, and I want the car to perform the way a 240Z should. And it seems to be the concensus that rounds tops are the best way to get there.

You might want to at least give some consideration to jayhawk's post. (#13). I hope he doesn't mind me quoting him in my signature.

Since I'm going to get the car running with the flats on, I guess there is always a chance I could keep them. If the car runs well with them, I suppose I wouldn't necessarily change them. If I do decide to keep the flats, will removing all the smog stuff affect them much?

My friend and I used to 'de-smog' them back in the 70s-80s when I had carbed cars. I haven't worked on a set of them (flat or round) in years but they did run better without the smog equipment.

Like TonyD, I'll be happy to help you eliminate the pollution in your garage by taking the flat tops off your hands. (I really need the linkage actually..)

But Weasel, you might want to look a little deeper into the whole flat top story than the oft repeated "boat anchor" or "emission carb" claims by posters who believe that round tops are "SUs" and flat tops are not. Or who believe that only the flat tops were made by Hitachi.

I'm going to try and scan into PDF format a copy of the "mythical" and "impossible to find" 1975 Nissan 240Z and 260Z Fuel Modification Plus manual that turns out not to be very difficult to find (2 have sold on eBay in just the last couple of months). It has all of the service bulletins, fixes, and tuning information on the flat tops in one manual (that should have been in the FSM, but wasn't....)

Conventional Wisdom may be conventional, but it is not always wisdom.

--Bob

Original Owner of 1973 240Z HLS30-125678, who drank the Conventional Z Wisdom kool aid and paid a lot of money to replace the flat tops with round tops. And now regrets that....

While the performance of "flattops/Hitachis/whatever"can be dramatically improved,they are still inferior(completely) to a PROPERLY set up pair of "roundtops/SUs/Three screws/whatever".

Performance. Well the JECS system used on the 280Z/ZX/810/RWD Maxima etc. is inferior to an EFI system with a MAF sensor and modern engine management, but that doesn't mean it can't be made to perform adequately. I.E. decent fuel mileage and drivabality, etc. Flattops can be setup to do that. If we're talking about building race cars that would be another story though some of the hi performance carbs available through Datsun Comp/Nissan Motorsports, though different from the emission carbs, were flat tops. The only thing that makes round tops more desirable is that no one has commercially put any effort into the maintainence, refurbishing, or improvement of flat tops. I have run satisfactorily performing flat tops in the past so I refuse to jump on the 'boat anchor' bandwagon. And PROPERLY set up is the key. I've seen a few cars with badly performing round tops.

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...:-)

Z train, you said "While the performance of "flattops/Hitachis/whatever"can be dramatically improved,they are still inferior(completely) to a PROPERLY set up pair of "roundtops/SUs/Three screws/whatever".

OK, why?

ie, what specific design features of the flat tops make them inferior? It seems to me that "properly set up" the flat tops ought to be better than round tops, since we know they have some nifty features that the round tops do not (separate idle circuit, power valve).

I don't know that they are better, but I cannot find any posts by any knowledgeable posters that point out the actual features or faults other than very generalized and incorrect claims that they are "emission" carbs and somehow cause all kinds of problems that they do not. (like the higher underhood temps of the '73s and '74s)

I look forward to your information.

Thanks --Bob

I have to ask the exact same question: Why, what makes the earlier carbs "Superior"? The fact that their full throttle and idle miztures are inexorably linked, so that you can't adjust one from the other without custom retapering of the needle? The fact that the earlier carbs have no provisions for extra enrichment under load, so you have to adjust them for worst case scenario and then live with sub-optimal miztures the rest of the time?

Or is it simply the fact that you can screw the knob on the bottom of the carburettor to make a jet adjustment? How often are you doing that...really?

A main jet adjustment is not something that normally requires resetting at every turn if it's close to the correct range...

So what, exactly makes them 'inferior (completely)' compared to the earlier carbs? Have you ever even worked on a set of Flat-Tops?

Are you aware that the HIF-6 Flat Top is a preferred carburettor to the round tops when available for the application? Separate circuits for idle and main jet are the primary reason there, and jet adjustment on those is via screwdriver instead of pin spanner. The hitachi Flat Tops are a Hybrid HIF6 Carburettor. But again, I'm awaiting exactly why you claim the things you are claiming. Give us examples. We have given you two good reasons as to why they are not inferior.

O.K.maybe i shoulda left out the "completely".And ,sorry to dis-appoint but i can't give you any technical info only personal experience and some info passed on from Bob Sharp racing.

And the obvious question-if the Flats are so bitchin' why does "everybody" ditch when they are able to?