xcmav66

GAAAAAAAAAAAAHHH!!! The frustration of owning an '80 model is starting to get to me. Are all parts from all first gen stock Nikki carbs the same? I need replacement parts, but many of the places I order from say that a substantial portion of 79-80 parts are "no longer available." I can understand with the redesign in '81 how suspension parts etc. may not be compatible, but why should parts like carbs and manual shifters be different? Please enlighten me, and if anyone knows exactly which parts I can NOT swap (without significant modification) from other 1st gens into my '80, that would be a huge help. Thanks.

TurboIIGuy

haaahha...........I was once there, when I got in to rotarys about 6 years ago.
Okay as far as carbs go, you can swap a whole carb from any 12a to any 12a.
That's why so many backyard budget guys, such as myself, are using an RX2 carb on my 1985 RX7. Mechanical secondaries as well as more throttle response and better top end power are the result there.
The main difference with a carb from the 79-80 when compared to the 1981 and later years are that the older ones have mechanical secondaries and the newer ones have vacuum actuated secondaries. Also if you look into the secondaries of your 79-80 carb notice that the venturis are a couple of millimeters larger than the newer ones.
So if its easier why don't you just look for another carb from a newer 1st gen RX7 and rebuild that and convert it to mechanical secondary operation.
I am not sure about the fuel jetting between the different years, so I can't offer any info on that.........Maybe somebody else could jumop in here with that info.

Siraniko

iTrader: (13)

nm

xcmav66

Thanks, that was enlightening. What I would also like to know is if I can buy individual parts (like float needles, etc) designed for a later carb (81-85) and drop them in mine.

TurboIIGuy

Actually the older carb give better performance......this is because they were not trying to be smog frindly.
The newer carbs are less fun to drive on in the respects that the throttle response and upper RPM power band is a bit weaker.
On every popular upgrade to an RX7 is to run a carb from an old RX2.
it has mechanical secondaries just like yours but dumps a bit more fuel for a stronger feeling power band.
Right now I am using a 1984 carb with a 1979 bottom piece, you know, the part that has the throttle flaps.
and it has RX2 jetting inside. I did this beacuse I don't realy want to spend money on my 1st gen until my 1987 TurboII is done and complete.
So this was a cheap trick.
I am running the carb with out a Racing beat air filter assemply and a full racing beat exhaust system and I am smoking new honda civic SI's and keeping up with automatic tranny G35s. Mustang GT's are a joke, they can't even keep up. And I am still running A/C and a full interior but all the emmissions have been striped from under the hood. AHAHAHA
hope this info helps you make a decision....Peace....

Sterling

Since I KNOW for a FACT that wacky KNOWS for a FACT how wrong you are, I have to assume you're either a friend of his..... or he just hates Nikkis so much that he doesn't give a crap when someone with Nikki trouble is ill-advised right in front of him.

What has mech. secs.?






What carb parts are you having a problem with, specifically? Most generic Nikki rebuild kits for the 12a carbs contain some extra gaskets so that the kit can accomidate a wide range (like pretty much all of them).

TurboIIGuy

okay if I am wrong I am open to being proven wrong........thats no big deal.
But the thing is I have about 5 carbs in my garage right now.
2 of them are from 79-80 RX7's and the venturis in the secondarys are clearly larger than the ones in the other carbs that are 84-85 models.
Also the 79-80 carbs have secondaries that open up on full throttle by hand just turning it.
The 84-85 Carbs don't have that.
SO from my experience the older carbs feel much better especially over 5k Rpm...........
Am I wrong about the jetting???
The venturis???
All of it even??????
ahaAAaHAHAah
Clue me in man...........

Sterling

Venturis are the same.
Jetting is minimally different with no assometer with the ability to tell any differnce. In fact, the most difference in jetting is in the idle.

Now, if you have such carbs, then they are absolutely defective, and I demand that you send the modif...er, I mean "defective"...carbs to me at once!

They may even be Yaw modded carbies.
Where did you get them?

And yes, most everything you put on a 12a will make it come alive somewhere after 4500 RPM.

TurboIIGuy

I will take pix of the carbs for you to all see.
one of the 79 carbs came from a buddy when he swapped in a 13b motor.
It has larger secondaries. It is very, very obbvious when you look down the throats of the carb as compared to the 84-85 carbs I have. They are probably about 2-3 mm larger than the 84-85 carb venturis. only the secondaries though.
The other 79 carb came as a spare with a parts car...the car came from a guy that used to SCCA it about once a month...or so he said.......
I have had them both for over a year and its is clear that they were rebuilt in more recent years. They were super clean when I got them compared to any other carb I have ever gotten my hands on. and the edges of the gaskets that stuck out were not all dirty and cooked like you would expect.
And the 84-85 carbs I have came from all the RX7's I have owned in the past 3 years.
I usually pull them off in favor of an RX2 carb for the simple reduction in vacuums and crap.

Am I wrong regarding the mechanical secondaries V.s the vacuum ones???
Are not the 84-85 carbs vacuum operated and the older ones mechanical????
Someone pass some info if I am wrong. SOLID INFO!!!

Sterling

They're all vac. sec.s.
They're all the same venturi bore size.
You have modded carbys, that's all. -Though I can't understand why someone would bore only the secondaries. I leave them stock in diameter and only change the profile. Much larger and they lose their ability to create vacuum to the main circuit at mid RPM.

If you look at the mech. sec.s carbys you have you'll see that the linkage on the secondary shaft on the accelerator pump side of the carb is wired together. Diagonal to that on the opposite corner you'll find either that the orifice for the vacuum secondary diaphragm is blocked off with a plug, or that they left the vac box on and simply disconnected the linkage to the shaft. (Sometimes they'll leave the box and linkage on but remove the diaphragm spring. No advantages either way.)

Jetting is roughly the same for all of them fuel wise. The idle circuits are different mostly because they did away with the air adjust screw on the T-body in 81, and replaced the valve with a big press-in jet. Then the only major difference are the primary idle cuircuit air bleeds that go from 150s on the early carbs (1.5mm) to to 170 & 180 on the later ones. (Big jets. The 2ndaries all use 60s [.6mm] idle bleeds. If you accidently tweak a primary shaft and gap a throttle valve, you can pop in a set of 60s (.6mm jets) in the primary air bleeds for more fuel in idle to compensate for the resulting high idle problem.)

Linkages are the same in their very basic form, but not interchangeable without modification and reconfiguring.
Some of 80s and most 79s had a power valve in the floatbowl. This replaced the power valve found on the throttle body of a few early 79s and previous years.
Either the computer interface replaced that utilizing the richer solenoid, or emissions standards crunched it, I'm not certain, but it disapeared altogether in 81.
The power valve of the 79-80 carbs required a reconfigured moulding of the floats that they continued to use...Each float has a dimple in the side to accomidate the valve, and there simply was no reason to change them back to the old style fat floats found in earlier Rx-"X" carbs.

Carb bodies and throttle bodies and airhorns can all be mixed and matched provided you know what you're doing, you're prepared for some modification of linkage, you will never need a functioning emissions system, and you enjoy migranes.
But i can be done.
I do it myself, but then I'm completely reconfiguring the linkages as a matter of course anyway, so what's the difference? The Sterling carb ressembles an earler Rx-"X" carb even with the later housing and airhorn. All linkages are minimized for the sake of simplicity.

The biggest pitfall to the carb modder is underestimating the sensivity of the idle circuit while focusing on the hi-flow modding. A very important part of the modding Carl and I do is slimming the throttle shafts for better flow. But once you disassemble the shaft and valve set, that throttle body has about a 10% chance of ever going back together as tight as it was before it was taken apart. That has been the source of many idle woes for me. It took dozens of carb mods for me to realize just how super-sensitive the throttle body set-up is, and as a result I've had a forced education in idle circuit correction jetting!
I've since learned to approach that portion of the carb modding as if I were doing surgery. It's truly the most delicate part. I used to think it was the venturi turning and e-tube tapping, but though that requires special attention, a lathe does the precision work.
I do use a milling machine for the shafts, but the actual precision is in the installation and assembly.

Another big difference you'll find in the Rx-"X" carbs is the emulsion circuitry; Particularly, the emulsion tubes. Some even have no cross-drilled holes in the tubes themselves and are simply open ended. This provides terrible atomization but ensures a rich mixture at lower air flow. The bleed sizes are much smaller on Rx-"X" carbs and are desireable for performance carbs. They give great performance by sucking more fuel.
One can really see the evolution of the Nikki carburetor as it was fine tuned for both performance and fuel efficiency for the 12a rotary engine just by lining up the various models of emulsion tubes in chronological order.
-However, one can also see how quality gave way to profit by lining up the castings that were used throughout the years, such as the booster venturis. The older Rx-"X" Nikkis were of a much better manufacturing quality.

TurboIIGuy

I need to find a digital camera to take a clean pic of these, a web cam just won't cut it......
I showed one of the carbs with mechanical secondaries to a buddy.
Before I asked him my question he saw it and said "oh....you put an RX2 bottom plate on this carb for mech. secondaries??"
So aparently thats where the mech. secondaries comes form because there is no wire holind anything together.
I know what that looks like I have done it several times before.
I work on RX7's every week, just not everyday. So I am pretty familiar with most anything you can imagine but somethings come along that are new to me completely.
Anyway my buddy also told me that another way to make some speed on a stock 12a carb is to pop in the 13b 4 port carb jetting and pull out the secondary venturis all together or something like that. He's going to do one up for me to try it out. I'll take pix and see if this ghetto redneck frankenstein of a carb is worth mentioning.......
sounds interesting.......
I have had holley carbs and side drafts before so I know what they feel like.
Nothing compares to the low end response of a stock carb in my opinion. Under 3k rpm stock rules. So yeah, this is interesting, I am learning some new cra about crap carbs......hahah....