what jetting would be best for a weber 45mm to a 1983 12A stock engine. my future mods are going to be exhaust and headers.

i need 2 sizes for CHOKES, MAIN JETS, AIR CORRECTOR JETS, IDLE JETS, PUMP JETS.

 

depends on actual tuning.

Start with 34mm chokes. 190 air, 145 fuel, emulsion tubes I forgot but I think they were F3s. idle jets are extremely important but unfortunately I don't have my table here, but I once played with them and just screwed up my whole setup. Pump I forget also.


that should get you going. With that combo should be plenty. Whatever you do avoid going to big on the chokes. Also hit the timing to a couple of degrees advanced.

my humble .02 cents... I ran a DCOE for about 4 years great carb!

 

Streetport 12A:

Idle 65F8
Main Jets 185
Air Corrector 220
Emulsion Tube F11
Pump Jet 45
Chokes 40
Auxilliary Chokes 5.0

That is what I am going to be running in my stockport 12a. Hopefully it wont hurt it!

 

too big Jeezus... I don't think it will have power down low, but give it a try.

 

what has to be changed?

 

you're both wrong... f8's are most likely going to be too lean for washington driving.
Personally I'd try
idle: 60f9
aux choke: 3.5mm
main choke: 40mm
Accel jet: 45
main: 180
a/c: 150
e-tube: f-11

You should come to some of the Izzys meet's if you're in WA. there are quite a few weber nerds here. I'm turbo weber'd..

 

What does the A/C do? I noticed a very large difference between what I have and what you put down. Also looking at your 60F9 and my 65F8. Is that still too lean?

 

A/C is the air corrector jet, locaten on top of the emulsion tube under the screw cap. 220 is way too big for a stockport, the bigger the air bleed the less fuel at high rpm, a 160 is what I used on my stockport with a weber 48.

 

F8's have allways been way too big in my experiances. I had 70f8's on my 45doe on a s313b and it was pig rich at idle but horribly lean at the transition onto the idle circut.

 

40mm chokes sound too big for a street driven stock ported 12A motor - the carb will have very poor low rpm performance with those big chokes because there will not be enough air velocity thru them to decently and smoothly suck fuel up out of the float bowl and thru the main jet fuel delivery system at low rpm street driving conditions below 2000 rpm.

 

Yes on that. I use at least a 50 increments between main and air jets plus emulsion tubes will less holes (# is top secret). This is to ensure that the engine runs "rich" on top end. To compensate for that, I like using larger idle jets and modded squirters for aggressive low end.

On the other hand, larger air jets will make it "rich" on low end but "lean" on top end.

But again, DCOE's and IDA's have different driving habits.

 

No they're not. I ran 40mm on my 13b and it had enough toruqu that I could let tehe clutch out up a hill and it would idle up the hilll then i could get into the gas w/o it stalling. The air in the area infront of the carb isn't too turbulant so a big choke could still drive fine. running a small choke on a rotary chokes the hell out of the top end(the only place we really like to drive)

 

http://www.matthewnanney.com/images/Carb/

 

What are the driving characteristics between a DCOE and an IDA?

 

we have a winner!!! right on

 

very nice matt... 10+++

 

alot different, dcoe= street carb, good driveability, ida, max power, less driveability, wacky special

 

coz wacky wants the maximum performance in case of the unexpected...

 

incase you weren't awair the unexpected is a Z06

 

Thanks for the response, but in my search for an intake manifold, i went to mazdatrix and bought a 48 ida manifold. does the same jetting apply?

can i put a 45dcoe on a 48 ida manifold? i doubt it, but i thought i would ask anyways.

Hyper4mance2k- at the moment my rx7 doesn't run below 1500rpm, so i would have to show up in my Impreza.

 

Nice job guys There is very little info out here in the public domain on rotaries and IDA/DCOE jetting. The racers guard their secrets closely, and the only one I know who I consider and "expert" in weber jetting (that will actually openly share) is Robert of Rotary Shack fame. Most of the big names won't even mess with tweeking your carb or any induction issues unless they build an engine for you.


Note to moderator - you need to archive this thread and a few others that come to mind from the past few years that relate to Weber jetting.

Robert if u check back in here...what do you think of Speedturns comment. I agree those chockes seem a little big for a stock port 12a. I'm assuming the users running that must compensate with smaller mains.

 

true, but i dont know many bone stock mazda drivers that putt thier rotarys around town a 2,000 rpm's let alone a rotorhead sporting a weber under the hood...
i have run as big as 42mm venturies on a stock port 12a (with dual exhaust and full MSD ignition) and seen power gains in the upper rpm's.. bottom end did suffer as expected but the results were what we were looking for.. on the other end of the spectrum,for someone that wants great low end, good midrange and dosnt mind the loss in top end power then 37mm venturies is what you want..


on a side note,anything bigger than 45-46mm venturies on a 48 mm carb you loose all bottom end and midrange due to the lack of velocity through the carb, but on a big j-bridge or a peaky p-port in a drag car thats ok, for a street car, thats a no-no = no driveability

 

thanks for the kind words..wacky is definatly in the top 5 when it comes to IDA jetting to

oh and a general rule of thumb is the bigger the venturi you run, the smaller the air jet you use, to compensate for the loss of low pressure area through the carb(thats what pulls the fuel up the jet, through the emulsion tube, aux venturi and eventually down the carb throat)

 

Yes its possible, flanges are the same.

You might get some fuel issues though (sidedraft/downdraft)

 

Since you guys are handing out free jetting advice, I recently picked upa 48 DHLA. Any suggestions for jetting for 1/2sp-1/2bp 12A. I know the Mikuni isn't cutting it.

Also got my grubby little hands on 2 different RE DCDs, one for a 12A, one for a 13B.