modifying/de-smogging Z Flat-top SU carbs? yea those..

[coolerow]

Building a budget SU setup for the wagon and came across some Z squaremouth flat tops on the cheap. Already have a K14 manifold, was just wondering if anyone had any info on mods to make these things a better carb application.There has to be some knowledgable people out there that has personal experience with these that can say good things and may know a few mods that can be done. That's what I'm looking for. Snooping around Z forums but not getting good results, thought I would try here.

I've owned SSS roundtops, mikunis, webers, dellortos, and even SK racing carbs so I know there's "better" options here. Just want to see if there some old school guys out there that can feel me in on any mods for these Z tuna cans. Let's try to keep the "throw those in the dumpster because ZTherapy says so" comments outta here. :)

 

Any info would be appreciated

 

Thank you.

 

 

[DISLEXICDIME]

if you want flat tops you need the 38mm flat top off a jdm l18 those can be de smogged and ran like a round top . not the  z flat top

[Skib]

tie a rope to them and toss em over the bow lol

[FiveSeventyZee]

let the record state: he didn't say to throw em in a dumpster....lol

[Xnke]

If you don't want them, you can send them to me...they are Far Superior to the roundtop carbs for performance applications.

 

I mean...they are garbage and you should put them in a flat rate box and pay me to take them off your hands, really...yeah.

 

The square-mouth tuna-can carburators FLOW MORE AIR than any of the roundtop carburators, 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 roundtop 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 roundtops!".

 

They are not junk. They are superior units, but they ARE NOT tuned, adjusted, or modified the same way the roundtop carbs are...because they are not the same carb! Apply the roundtop 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 roundtop 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 roundtops 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 roundtops, 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.

[coolerow]

If you don't want them, you can send them to me...they are Far Superior to the roundtop carbs for performance applications.

 

I mean...they are garbage and you should put them in a flat rate box and pay me to take them off your hands, really...yeah.

 

The square-mouth tuna-can carburators FLOW MORE AIR than any of the roundtop carburators, 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 roundtop 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 roundtops!".

 

They are not junk. They are superior units, but they ARE NOT tuned, adjusted, or modified the same way the roundtop carbs are...because they are not the same carb! Apply the roundtop 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 roundtop 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 roundtops 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 roundtops, 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.

 

Holy crap THANKS! This info is greatly appreciated. I knew there would be some knowledgeable people in here.