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We're bringin' back the Flat Tops!

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Good to see flat tops being utilised, I've heard they are actually superior to the early round top SUs as the idle circuit can be set independently of the rest of the throttle range. I think the flat tops suffered from the old grape vine, in that a lot of folks never actually took the time to understand them, restore or fix them so they work properly and just ditched them based on what "other people said". But many of these people would not have verified the facts for themselves.

I would be very interested in the opinions of those who have had experience with them and got them running right!

The only downside I see with them is that they make the engine bay look a lot more complex than the earlier simpler carbs. 

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There are several technological advances built into the flat tops, but as always... With more technology, comes more complexity. And attention to detail is paramount.

I'll never expect a huge groundswell of flat top love and people ditching their round tops to replace them with flat tops, but I do believe that if they are working properly, the flat tops are better carbs. However, because of the additional complexity, you must be willing to put in the time and effort to set them up right and keep them that way.

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Makes sense to me, which is why it sort of upsets me that so many were likely thrown out over the years. What a waste.

Interestingly this 260z 2+2 came onto the market in Australia a while ago and 1 of the things that appealed most to me about it, was the fact it still had the original flat tops and steel wheels and caps!

https://photos.app.goo.gl/CWdhoXxY9WjdXoKE2

All the emissions gear was there and in place too. Beautiful.

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Agreed. And the damage to the reputation is already done, and (I believe) is irreversible.

So, that 2+2 you posted about... I don't know anything about cars that were stock gear in other countries, but that 2+2 would not have had all the pollution equipment in the US. If it were here, it would have had EGR, and throttle opener, just at quick glance. And air injection with the pump.  So if you think flat tops were complicated in your part of the world, you aint seen nothing!  LOL

So how long did the flat tops run in Australia? I assume they started in 73 just like they did in the US, but here they stopped in 74. In Australia (and elsewhere in the world), they ran the flat tops for a number of years beyond 74, didn't they?

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Sorry, but I think the fact that so many tossed the 73 flat tops in the 70’s speaks for itself.....flat tops just were a major step down from the earlier carbs.....glad you folks are going for originality, but I wouldn’t even think about trying to make them work. I just picked up a 73 for one of my friends who bought an original 73......had to use starter fluid to get it started.  No thanks.....and good luck to you for trying!

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34 minutes ago, Diseazd said:

Sorry, but I think the fact that so many tossed the 73 flat tops in the 70’s speaks for itself.....flat tops just were a major step down from the earlier carbs.....glad you folks are going for originality, but I wouldn’t even think about trying to make them work. I just picked up a 73 for one of my friends who bought an original 73......had to use starter fluid to get it started.  No thanks.....and good luck to you for trying!

Maybe @Zup will take you for a ride in his 73 in Oct. He is running flat tops from Paltech and I don't think he has any issues with them

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Flat tops got to the place and reputation for three reasons.  IMHO

1. Complexity. When they wear out, and they all do, rebuilding them was difficult. Kinda the same, keeping them in tune was also tricky.

2. Availability of the earlier simpler round tops. Why bother when something simpler and better is available, barring some polution law in your kneck of the kwoods that made you do it.

3. Rebuild kits were NLA for a long time. MSA has them again, I bought a set. 

I have a bushel of flat top cores if someone is wanting some....  Crickets......

I have previously expressed my admiration for the design of the flattops.  While I threatened to build a set and show the na sayers some time slips, well, you know what happened. Too complex, time consuming and there are these fantastic folks at ztherapy....

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20 hours ago, Gav240z said:

I would be very interested in the opinions of those who have had experience with them and got them running right!

My only experience with the flat tops is that I had a '73 with them on and they ran great, even in bad traffic on the 5 Freeway.  Hard for me to complain when I have only had a good experience with them.

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3 hours ago, Diseazd said:

flat tops just were a major step down from the earlier carbs....

LOL.  And it's exactly this kind of claim that I'm talking about when I said the damage to the reputation is already done, and (I believe) is irreversible.

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20 hours ago, Diseazd said:

Sorry, but I think the fact that so many tossed the 73 flat tops in the 70’s speaks for itself.....flat tops just were a major step down from the earlier carbs.....glad you folks are going for originality, but I wouldn’t even think about trying to make them work. I just picked up a 73 for one of my friends who bought an original 73......had to use starter fluid to get it started.  No thanks.....and good luck to you for trying!

So you had a hard time starting a 45 year old car, and from that you concluded the flat tops were a "major step down"? Hmm.  My flat tops ran just fine during the 70s while commuting and making sales calls all over southern California, but like many of us, I was convinced by a 1980 mechanic's presentation at the Orange County Z club meeting that the round tops were so superior, and paid him over $500 to replace my carbs.  Funny thing, he (and zTherapy) made a lot of money, but I had NO performance or drive-ability improvements. 

One can only speculate why mechanics (and zTherapy) love to disparage the flattops...

 

 

 

June 2007 004.jpg

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Jayhawk, That's a beautiful flat top pic. Is that yours some many years ago? I looked it over pretty closely, and the only fault I can find is the failed insulation on the throttle opener and EGR solenoids. That's the only little nit-picking issue I could come up with!   LOL 

1 hour ago, 240260280 said:

I thought it was the extra pollution stuff on the 73 manifold that caused the complexity and problems which painted the flat tops with the same brush.

I think it's a whole bunch of things. The extra pollution controls, the more complex throttle opener system, the more complex idle mixture adjustments, the power valve, the water running through the carb bodies. All the extra plumbing associated with all that stuff. A whole host of things.

Capped off by the fact that you can't compensate for faults elsewhere by adjusting the nozzle depth like you could on the round tops. You have to get things right... You can't just cover them up like you could with the round tops.

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The pic is of a '73 that I saw in Portland OR a few years ago.  The owner had 3 1973 Zs all restored like that.  I don't plan on polishing/chrome the valve cover like that one.

I agree that the extra pollution controls and other complexity (plus the early vapor lock issues) were the real cause of the problems ascribed to the flat tops.  To me the complexity is a learning curve issue from the features of the flattops like the power circuit and idle adjustments that (in theory) allow the carbs to be tuned for both power and idle.  

I wonder if anyone has ever run a dyno test on a single Z using both the round tops and the flat tops.  With everything else as equal as possible and the carbs mounted on the same intake, with the same pollution equipment (if possible), etc.  Might be fun to do that and see what the differences are that are just due to the carbs.

 

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Yeah, I'm not a fan of the polishing either, but I couldn't rightly flag that as a "flaw" since it's a style choice. Valve cover, oil fill cap, carb bodies, backfire valve polished...  I personally don't care for any of that.

I'd love to participate in that dyno test to compare round tops to flat tops, so if you hear of something like that brewing, let me know!   LOL

It's not necessarily going to show anything though since the dyno test is just running full bore output at WOT. Under those conditions, you're not using many of the technological improvements of the flat tops and both sets of carbs should easily be able to be tuned to produce the same results. It's kind of a "static" test.

In theory, the flat tops should shine in other areas like idle cleanliness, mixture consistency under varying operating conditions, gas mileage, and transition power on pedal stab. None of that would show up on a dyno test.

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On 7/2/2018 at 7:33 PM, jayhawk said:

Hi, I’m the “gentleman” (Rich may be a little too generous 😀) that is the original owner of the ‘73 Z of this thread.  I’m happy I managed to hang on to my Z this long and yet ashamed I have let it sit so long.  I bought it new from Gubrud Valley Datsun in Mt Vernon Washington shortly after returning from an 11 month deployment with my US Navy A6 Intruder squadron aboard the USS Kitty Hawk.  ( which was a great way for a young ensign to save his pay to buy a Z!).

I’ll post more info about the history of this car when I get back home after the 4th.

 

Hello Jayhawk,

we are about  in  the same position except no one ever called me a "gentleman".  I've got a '73 I bought in '76.  I was lusting for one ever since the RT article in 70?  Anyway, I had to graduate with an EE degree and get a job before I could buy mine.  I kept mine garaged until 2000 when the garage got filled with inherited stuff which eventually got pitched.  Sadly my Z suffered for it with the rust.  It sat the last 3 years with a broken clutch  and the wife threatened to haul it off I didn't move it.  So I said no problem, decided to change the broken pressure plate, of course exhaust studs broke off, long story short.  The engine is now pulled out and I"m going to paint at least the engine bay so I can get it running again.  Its a sin for someone like me to abuse a perfectly good car like I did.  Good thing I'm retired.  btw, I've got round tops.

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9 hours ago, Patcon said:

You could include some O2 datalogging to pick up those qualities

True, but the only thing most people would care about is peak HP. Maybe you could convince them that the power stab transition is important, but other than that?

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17 minutes ago, Captain Obvious said:

True, but the only thing most people would care about is peak HP. Maybe you could convince them that the power stab transition is important, but other than that?

Maybe, but an engine that runs closer to stoich requires a lot less maintenance and responds better to fuel inputs

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Haha! Well if someone wants to set something up, I'd be happy to participate! Not sure I'm qualified, but I can twiddle some knobs and stuff!   LOL 

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Looking at your photos I see what must be a universal problem regarding these restorations, that battery platform.  Mine is also rusty.  I can clean out the visible part but I am wondering what it looks like on the reverse side (the part you can't see)  of the battery platform and what to do about it.  Is the paint ok there if the rust did not eat thru?  Do you clean that reverse surface and repaint it?  fwiw, mine is simply rusty no holes thru it.  So I'm not sure what to do about it.

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39 minutes ago, hls3073z said:

Looking at your photos I see what must be a universal problem regarding these restorations, that battery platform.  Mine is also rusty.  I can clean out the visible part but I am wondering what it looks like on the reverse side (the part you can't see)  of the battery platform and what to do about it.  Is the paint ok there if the rust did not eat thru?  Do you clean that reverse surface and repaint it?  fwiw, mine is simply rusty no holes thru it.  So I'm not sure what to do about it.

It is very difficult to deal with the underside of the battery tray and an OEM type replacement panel is unavailable. I believe the factory assembled the car and sprayed it the same way we try to do it today. After having done this, I can tell you it is almost impossible to get paint up in there. Even treating the underside of the tray is difficult

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Got a lot of stuff removed last Thursday and today.  Got the Fuel tank, fuel pump, hoses, diff, half-shafts, trans tunnel fuel and brake lines, seats and steering column removed, among other things.  Took some good pics of the fuel pump since that is unique to the '73 (as opposed to the '70-72).  Also took some good pics of the steering column wires because, as we know, the green wire connects to the white wire.  Now  I just have to remove the dash, front and rear glass and interior vinyl and that will be it for the part removal.  I will clean things up and get most of the grease and dirt off before I  transport the body to Miguel.  I am hoping I can get this to the paint shop this Thursday.  The underside was pretty dirty with caked oil, so that may take a bit of time.  

It's interesting to follow all the Flat Top 'banter'.  It will make the final results all the more exciting once it is complete.

@CHL240Z, Yes,  I am keeping Miguel busy.  My white Z is down there already.  Now it will have company.

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If I recall correctly, that electric fuel pump by the gas tank was installed by the dealer as part of the V3 fuel system mod/kit that also added the fuel line insulation and maybe a 5 bladed fan. 

So there are two fuel pumps on this Z: the original mechanical fuel pump in the engine bay, and an electric pump at the fuel tank that was added as part of the factory V3 mod/kit (installed on this car by the dealer) to solve some of the vapor lock problems. My logbook entry shows it was installed on this car on 11 Jul 1974, mileage 11,022 miles.

I think that later '73s (and 74s?) may have had the V3 mod done before delivery, either at the dealer or maybe the factory.

 

 

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Hi Jayhawk,  are you saying that you have access to Nissan records so if I give you a s/n for my 73  you can tell me  how/where it was installed?

I don't remember how mine was electrically connected, but it never worked.  I made it come on with the keyswitch but  then would go off if I lost oil pressure so if I had an accident and the  motor stopped  it would stop pumping gas.  Mine does not have any fuel line insulation.  Was the insulation applied inside the engine bay?

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