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Dual SU project - $175 shipped

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getting rid of my dual SU setup project I will not be using.

K14 SSS manifold that is bead blasted. Comes with linkage rod and several linkage parts. The 260z carbs are significantly bigger than the regular L18SSS flattops. Bought them locally from a guy who put roundtops on his 260Z and had these sitting in his garage so they might need cleaning. Everything in overall good condition. These carbs get a bad rep from people who don't understand how to sync them properly. I can include a pdf copy of the manual on how to modify these beasts.


$175 shipped to 48 states.



Quote from Xnke


Posted 06 March 2013 - 05:45 PM

they are Far Superior to the round top carbs for performance applications.


The square-mouth tuna-can carburetors FLOW MORE AIR than any of the round top carburetors  they have a real, functional choke system, they have separate idle circuits and main jet circuits, and can accept the same jet needles as the round top SU's. They are not tuned the same, they are not adjusted the same, and many people make the mistake of saying "oh, those are smog carbs, they're junk and you should get some nice, easy-to-work-on round tops!".


They are not junk. They are superior units, but they ARE NOT tuned, adjusted, or modified the same way the round top carbs are...because they are not the same carb! Apply the round top methods to them and they will treat you badly. Set them up the way they are designed to run and they will allow you to run much more power than a round top will without having to drown the engine at idle with a rich jet setting, or fight with the warmup characteristics as sometimes will happen with a rich mix and cold weather that the round tops run into.


As far as de-smogging, you can make cover plates for the extra ports you aren't using, clean them thoroughly, and get a wideband O2 sensor and install it to get the main jet profiled correctly.


Set the carb at bone stock factory settings BY THE FSM FOR THOSE CARBS! Don't use the settings for the round tops  it's not likely to work correctly. Once the main jet is set at the factory location, make sure the choke system is clean and not binding, and set the idle screw 1 turn out and start the car. It *Should* start up at 1 turn out, but should not take any more than 1.5 turns out to get it started. Let the engine warm up, and check the wideband O2 sensor and get the idle circuit dialed in for both airflow synchronization and idle mixture, then step the engine up to 2500RPM and check the airflow sync on them again. Set main jet mixture at 2500RPM, and CHECK the mix against the wideband, at 1500, 2500, 3000, 3500, and make sure it tracks properly.


As long as you don't have any leaks on the smog-ports (three bolt pattern on the top rear of the carbs, IIRC...been a while since I worked on these) when you cover them with blanking plates, you should be able to work through this and not have any major issues.


If you need even more air, these carbs can be 'ported' by smoothing the bridge out (not removing the bridge, but smoothing the sharp edges out) and uniforming the inside of the body forward of the throttle plate. Don't try to port the throttle plate area out bigger, unless you're going to make custom plates and such. Make both carbs as closely matched as you can get, so you don't run into air sync problems later.









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just an fyi those aret the carbs your qoute is about... those are the shitty smog carbs of the 260... these are the ones with the 3 bolt covers that are the good flat tops...Picture136.jpg


more pics found here. http://community.ratsun.net/topic/31627-for-sale-flat-top-sus/


as you can see you have the square opening ones and the good ones are the round opeing ones....

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just an fyi those aret the carbs your qoute is about... those are the shitty smog carbs of the 260... these are the ones with the 3 bolt covers that are the good flat tops...



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that was posted by coolerow, 2nd sentence.  I don't think he was trying to mislead or anything. Read it several times b4, I chimed in.


It also has a quote by Xnke that basically refutes comments by Ztherapy that says:


This is not a carb-It is a boat anchor!


It's generally accepted that the flattops were overly complex, hard to tune and from difficult to rebuild to impossible to rebuild when worn. They were a smog carb that was more interested in mileage. Yes they can probably be modified to work better but earlier round tops are good from the start.

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Not even close, Datzenmike. The roundies are good for being easy to tune...but the squaremouth carbs can consistently deliver more power and better drivability any day of the week. They require different tuning, and different maintenance, and they're ugly. They get a bad rap because people DON'T know how to keep them in good condition and honestly don't care to, since the roundtops are just a few bolts away and they're simpler.


It's the difference in bolting on a holley and bolting on a weber. Both have their merits...but I'm sure you know which carb you'd want to use. It's most likely the one with the most documentation, and the one you're most familiar with...

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I think we are in agreement. Sort of. Like you say, most don't care to go to the bother when the round tops are there. It's easier to find info on the round tops too. I've only once ever before heard that the flattops could be 'de-smogged' but no info provided.


I see you mention a triangle plate that needs blocking. I have a set of late L16SSS or L18SSS flatops that haven't been un smogged. Are the 260 SUs like that? And what does the screw adjust?


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The Z car SU's are not the same, and I have no idea what that screw is supposed to do. The Z SU's are actually a clone of the HIF-6, which in every other car make/group/circle/whatever is UNIVERSALLY preferred over the HS-6 (roundtop style carb) for the seperate idle circuit, power valve/accel enrichment valve, and seperate main jet. Because all three are seperate, but interact, it's much more like tuning a Holley than it is tuning an SU...but you still have to deal with the SU's metering needle.


Basically, you can run a much larger street cam with the Z car flat-tops than you can with the roundtops, and get good drivability and power. When you start getting into the big frumpy street grinds, the roundtops start to sacrifice drivability and idle mix, unless you start re-profiling your needles...which isn't that difficult but I doubt most here would tackle it. with the flat-tops, just slap in a slightly richer needle, and adjust the power valve for accel, and the idle circuit to run the car up to about 2500RPM...no worries about washing down the cylinder walls at idle just to get it rich enough to not bog on hard acceleration. With roundtops, you can work around the bog up to a point...but you're compromising idle mixture severely. With the flat-tops, it's trivial. Even considering the even grumpier, all-out nasty race cams (we're talking 0.570" lift and 320* duration range here) you can get a half-decent idle with the unmodified flat-tops, when the roundies are going to be doing their best to keep the thing ticking over at all!


Don't get me wrong...the roundtop carbs are great little bits of kit...but the flat-top carbs are a superior design, and that's all there is to it. They DO take more work to get right, but once the job is done, it's done...just a tune up every now and then, same as the roundtops.

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Finally some info on them. Not much out there on the flattops. Yes the L16/18SSS are smaller 38mm and two mounting bolt. The screw in the picture looks like it adjusts air flow... maybe an idle thing? There are write ups for disabling them, the simplest is just plugging them with JB.

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