jet sizes
 

does anyone know off hand what size primary and secondary jets come stock on a 1980 carburetor?

I've got an 80 12a in my RX-2 but I'm using the 73 carb with 90/150 jets and I can't get the thing to not run rich as hell. Idle speed and mixture screws aren't helping much. I'm thinking maybe 80 uses smaller jets or something . . . hoping somebody here has a carby they could look at and let me know what size I should be using.

thanks in advance!
Dave

I dont have one open to check, but 90 and 150 is rather small. Stock for 84-85 is 92 and 160. All these carbs are the same size so a 79 should be the same.

I do believe that the '79 to '80 carbs run richer due to the thermal reactor setup, but I'm not sure of the details. I do know that my carb is running 90 primary and 160 secondary jets, and it runs fairly rich.

perhaps it's just the idle circuit then. Metallic_Rock has an 80 carb he's gonna loan me, so I'll rebuild it and see how it idles with that.

Currently it seems to run fine above 1500, but below that it shudders and lopes. We thought it was a vacuum leak for sure, but after pulling the plugs and finding them sooty, now I'm not so sure .. . .

Hmmm....

This could be a long shot, because I don't know anything about the '73 carbs, but when I rebuilt my '79 carb, I put both secondary jets in the one float bowl and both primaries in the other bowl. It did the exact thing you described, idled alright, but had no power and vibrated quite a bit above 1500. I don't know if this is applicable, but I'll pass it on as a guess.

that's actually the opposite symptoms of what I have - thanks for replying though ;-)

Darth Linux (nice handle BTW) :) I just took a look at your yellow RX-2. Man! That's is sweet!

http://12.230.41.37/graphics/mazda/rx2_new_ext2.jpg

The problem is with your emulsion tubes. In the earlier carbs, there are no holes cross drilled in them. Tisk-Tisk.
Replace them with the corresponding later carb E-tubes, and fuel jets, and let us know how it works out.

I R having GR8 readin' SkiLlZ!

can you tell me why a 1980 engine needs cross drilled emulsion tubes and a 1973 engine doesn't? I'm using the 73 carb and intake manifold, no emissions and a 84 log style cast iron exhaust manifold (no thermal reactor).

As much as I wish I did know, I still have more to learn about that. I just don't know yet. But I can tell you that with my modded carb on my DD, when I recieved an Rx-3 carb, I tried swapping the E-tubes to see what would happen.
It was terrible. They suck way too much fuel.

My "self-educated" guess is that the earlier rotaries had much lower fuel pressure deliveries. They may have also had stiffer vacuum secondary diaphragm springs so that the seconds would open really, really only during significant load. (It was, afterall, a family sedan during the 70s.:) )
Also, I believe the primary E-tubes are drilled. Just not the seconds.
Lemme look at the old Haynes Rx-3 manual I picked up at a car show just yesterday about the fuel pressure...

...oh yes,
I'm cool!:)...
Feed Pressure is listed as 2.8 - 3.6 lb/in2.
So I think maybe that's why no cross drilled holes, but I'm not really 100% sure. -

2.5 to 3 psi was the regular fuel pressure for my vintage. Racing beat of course recommends a 6 psi fuel pump with a pressure regulator set to 3 for performance applications.

I know early carbys were jetted over rich to give the thermal reactor unburnt fuel to burn. I removed the 94s I had in the primaries and went to 90s since I no longer have a TR and don't need to waste gas. But this is strictly idle circuit stuff. The primary jets aren't even delivering gas to the e-tubes until you are above 1500 or so right?

So maybe it's just a hogged out idle circuit in the early carbs and a smaller more emission conscience one in the later years. I also heard that later 12A had smaller ports than the early motors, so it stands to reason that they would demand less fuel/air in a general sense.

thanks for the tips - I'm gonna continue playing with it, and I may just put an 80 carb on it and see what happens.

Hey Darth is that Rx2 a 71 and does it have a old Ronald Reagan it's time for a change bumper sticker on the back. Does the center of the rear bumper have a crease in it. If any that sounds familiar it used to be mine. I sold it back in 94 when I was in the army. I used to live out by Chehalis when I sold it. Please let me know I feel a Maury show coming on. Parents reunited with their lost children.

it's a 72, and there's a crease in the trunk.

I will bring that 80 carb by either tonite or tomorrow night... depends on when the Jeep gets fixed. Oh, and you can HAVE it. I'll send the 85 model to Rx7Carl/Sterling when I get the money. That's the only reason I was saving it. If you need it, though, you can have it.

If you aren't home, I'll just leave it on the doorstep.

it's actually a 73 and I bought it from the original owner's son (in his 60's actually) about 3 years ago. Grandma bought it new in 74 in the Tri-cities and drove it till she went blind. Then it sat at sonny's house for about 8 years and then I found it . . .

thanks for the carby Chris!!!

you're welcome... why do I keep thinking it's a 72? Oh, well...