Any Weber guys here?
 

As some of you know, I've been getting ready to do a 5-8 PSI blow-through setup with a 45 DCOE and S5 turbo on my streetported R5 13B, and I've got a couple of questions.

First: I have two options as far as which carb to use. The first one is an old-style "made in Italy" 45 DCOE. It looks to have pretty high mileage and the throttle shaft seems like it's a little tweaked, and doesn't close fully without an external throttle return spring. Seems to work okay otherwise. The other carb is a newer "made in Spain" model that seems to be in a little better shape overall, though it's a bit dirty. It also has some weird brown/orange sand-like gunk in the float bowls, which will have to get cleaned out. I have heard the Italian ones are better somehow, but I can't find details as to why. Which one do you guys think I should use? I'll probably use the plastic floats out of the Spanish one either way.

Second: I'm currently having a very choppy cruise at less than about 1/4 throttle. More than that and it's smooth and has decent power. Deceleration is smooth, idle is acceptable. I read one post that suggested that the float levels might not be set right, which is possible since I haven't checked them yet. Any other probable causes? Current settings are listed below:

Main venturi: 40mm
Aux. venturi: 4.5mm
Idle jet: 65F9
Main jet: 180
Emulsion tube: F11
Air corrector: 175
Accel. pump jet: 60

Since I'm still NA, I'm not going to bother trying to get it perfect yet. I'd just like to solve the cruise problem for now and get it tuned for real once I have boost and an air/fuel gauge.

It sounds to me like your float level is off a little causing your stumble. All else seems to be good.

Be careful not to exceed the 8 psi. The floats will crush under anything much more than that. No one makes any metal floats for the Webers to get decent boost.

Don't let a little dirt & varnish throw you off. A bent shaft is bad news.
As far as I know, there should be no difference in quality/craftsmanship.

I have a 48DCO in the REPU. In my experience if the floats are set too high you get fuel dripping inside the throttle bodies. Just look in there and you can see some dripping going on. It will even flow back out the intake side and drip on the motor. Too low and you will run out of fuel quickly on a full throttle run.

The first thing I would do is stick a wide band in there if you dont have one already. I had the REPU running somewhat OK for 5 years, but with my recent rebuild I installed a wide band and in about 15 minutes of jetting I have it running way better than it ever did in all the time I owned it before! Its really quite a chore to get things right without one, and I suggest you have it tuned perfectly before you even start working on your blow through setup.

Dont make a decision based on how clean the carb is. These can be completely torn down, cleaned and rebuilt in an hour.

Yeah, I know a dirty carb is not necessarily a bad carb. In fact, often the dirt and grime help preserve it. :)

But after looking at them again, both carbs are in about equal condition, including the throttle shafts. I'll probably use the Italian one with the plastic floats since the linkage is already set up.

No drippage in the throttle bodies as far as I can tell. I swapped in the plastic floats and it feels like it might have improved slightly, but the problem is still there. I haven't noticed fuel starvation issues on full-throttle runs. What should the level be for the plastic floats?

Yes, a wideband would be nice, but they're too expensive for me. :) A narrowband will have to do, as non-ideal as that may be.

when you run a 45mm carb with 40mm venturies its going to be choppy at part throttle. install a 36mm venturi and she will drive much smoother. the choppyness is the carb switching back and forth from idle circut to main circut.

Accel pumps could be as high as 90's

Hmm, this thread is back, eh? May as well update. As it turned out, the problem was that my idle jets were just way too big. I'm using 50F9s now, and it's nearly perfect. Go figure.

Took a bit of a detour to play with superchargers and 4-barrels for a while, but I'm back on track to finally get the turbo installed, probably over the winter.

Robert: I may try some smaller main venturis, but not because of drivability problems (because I don't really have any anymore). I'd just like some extra low-end. Under 4K there's just not that much there. The turbo should help with that, though. :)

Really? Let's do an order from that pipe place soon. Let's also start fabbing up a carb hat. It'll be winter before you know it.

I am having a similar problem. Choppy at cruising speeds. But on a long deceleration, it seems to "build up" or something, cuz when I get back on the throttle, it bogs and then farts a huge backfire out the exhaust and sometimes dies. Most of the time I have to pull over and wait a few minutes then fire back up. I do have a wideband, but it is digital and not sure how accurate. (question, i had to install a switch on my wideband guage to go back and forth from each rotor because I am using 2 0xy sensors. has anyone solved that problem?)
here are my jetting settings:
Weber 48 IDA on a 13b street port. (4 port)
250 MAIN ( I know this is big, but my problem is at lower RPMs. Ordered a 190 and 220)
70 Idle
50 Pump Jet
F-11 emulsion tubes
160 Air Corrector Jet

Please help if you can! Thanks

what is the acc. bypass jet in the bottom of the float? it has to be a zero

can't seem to find what you are talking about. can you refer to this schematic and let me know what you're talking about? Also, how important are the air horns? (number 58 on the schematic)
http://webernorthamerica.com/pdffiles/48IDA.pdf

Also, I just measure and found out I have 47mm venturis. Seems huge, but thats what the carb came with on this car. Also, I am not running the airhorns. Is that bad? what do they...and the venturis do exactly. And what is affected by their size??

Are you worried about the O2 sensors failing when one isn't being used (up to temperature)? or are they working and you are just not reading one of the outputs?

It's just annoying cuz I can only read 1 output at a time. I have to flick the switch to read the other one. This makes it hard to tune and read while driving

"Pump exhaust valve", number 11 in the diagram. Its purpose is to bleed off some of the accelerator pump shot. A "zero" bypass jet indicates that it has no bypass hole in the side.

The air horns smooth the airflow into the carb, increasing power. They come in different sizes so you can fine-tune the length of your intake system.

Also, are you sure you have 47mm main venturis in a 48 IDA? That doesn't even seem possible, and certainly not recommended.

you're right. I did not measure the venturi correctly. I measured at the bottom. When I measured that narrowest part, it measured 42mm, which I understand is still big. But venturi size should not affect a rich or lean condition.

also, I have been told to increase my pump jets from 50 to 90, which is only possible by drilling. I'm not gonna do that. But it's funny how so many opinions and advice can contradict others. Either way, I have learned a lot from everyone.
By the way, F#@k RX7club.com and their rules. This forum is 100x better

42mm venturis sound fine.

What exactly does your wideband do when it bogs? Does it go rich briefly and then go lean, or the opposite, or just lean, or what?

Ok, so I got some new jets. I just swapped in a 60 idle and 220 mains. And now my problem seems worse. And my wideband is reading richer than before at idle. The choppyness is worse too. How can it be richer with smaller jets? AARRGGHHH!!

I actually think my condition is lean. There is a huge "cutout" when gassing it from low rpm to midrange and higher. Plus my wideband is saying lean as well. But I don't know how that's possible with 70 idle jets and 250 mains. wtf???
I have heard about drilling out a 3rd progression hole. But I don't have the ballz to do that...and am unsure if that would solve anything anyway