Interesting Weber jetting

[Gaz64]

You're on the money, and I guess that's how Weber decided on the final small sizes.
Sounds like 35s will fix your issue, I'd be itching to get the lids off.

[jimf]

Eljaro, looking forward to the results of your new modifications.
After reading all the info here in this thread, I decided to increase the chokes from 37 to 40 before I even install the conversion on my 393 w stroker. When I recieved my new 40's they looked as rough as the 37's did, so I decided to machine them internally. Made up a profile tool bit the same as the contour of the 40 and machined away. Well the 40's had to be machine to 41.5 mm before they would all clean up round and true. These castings are very poorly made and not consistant. Some of them would have cleaned up to about 40.75 mm and the others had to go as far as 41.5 to clean up. This will give you an idea of how much different one of your carb bores could be different from the other, right from factory. So now my delema is ....do I use the 41.5's or do I machine out the set of 37 mm chokes to 40 mm like I was going to try? Would you think the 41.5's might be too big?.....Anyone have comments?

[Cal Metal]

Percentage wise, that is a pretty small jump from 40mm to 41.5mm. I would be inclined to try it with the 41.5. Were these chokes just recently purchased? I have used a polishing compound mounted on a drill bit that cleaned them up to the point that they were as smooth as glass. These must have been pretty rough.

CM

[Gaz64]

I have polished every Weber venturi I have purchased over the last 25 years.
DCD, DCOE and IDF, they all polish up like a mirror with minimal metal removal.

41.5 is a about 7.5% larger than 40 in cross sectional area.

You can only try your 41.5s and see what happens.

[Eljaro]

I did machine my 37mm chokes to 39mm, and ended up having to go to 40mm because of the final finishing. Make them all 41,5mm, or take your 37mm and make them 40mm.
I have been working on my new KC 487 sideoiler, where all the settings I had did not work any more. I tried the new F14 tubes I got and they were too lean in the low range. I did turn the outer diameter from 8.2mm to 7.9 and it was much better, but still probably needed some more holes below the top row to work well.
Before going to drilling the F14 tube I did take the F11 tubes, soldered the lowest row of holes shut so as to make an F15 tube out of it and it seems to be the best so far. I have 140 main jets on it right now but will go to 135. The air corrector is at 120 now. Idle is 65 with 120 holder. Pump bypass jet is 0.35.
I have had issues with the pump jets. On idle I have seen some of them dripping gasoline and on shutdown when the webers absorb the heat from the engine and get warmer fuel drips from the pump jets into the throats. No good!.
So I removed all the pump jets, took a 2mm tap and screwed it inside the brass plug in order to pull it out.
Some of the seats for the small ball inside looked terrible, so that closing the hole with the ball must have been impossible.
I drilled a conical shape with a 3mm drill on the brass plug and and replaced the 2.38mm steel balls with 3mm ones. They are slightly larger and twice as heavy and I must test how they work. I believe that if the vacuum is very high such as with our Hi-Po engines the vacuum is drawing gasoline out of the pump jet because of defective manufacturing process and throwing any idle-transition tune up out of kilter.
If the weekend is sunny I will try it out and post results.

[Eljaro]

This is how one of the the pump jet seat for the ball inside looks like. It has a spiraling cut which makes it impossible for the ball to seat right and close the pump circuit. The vacuum in the carbs was thus pulling gasoline through the pump jet. Some ball seats looked better, but I drilled on all of them a conical seat for the 3mm ball to fit right.
The result has been that the webers do not dump gasoline any more into the throats when resting and absorbing the heat from the engine.
So that one problem seems to be taken care off.

[priobe]

Originally Posted by Eljaro

Attachment 14633
This is how one of the the pump jet seat for the ball inside looks like. It has a spiraling cut which makes it impossible for the ball to seat right and close the pump circuit. The vacuum in the carbs was thus pulling gasoline through the pump jet. Some ball seats looked better, but I drilled on all of them a conical seat for the 3mm ball to fit right.
The result has been that the webers do not dump gasoline any more into the throats when resting and absorbing the heat from the engine.
So that one problem seems to be taken care off.

Ejaro,

Did this correct your problem with the dumping of the fuel?

[Rick Parker]

"Made in Italy"

[jimf]

These were recently purchased (the 40's) as well as the complete conversion set up with the 37's in it. Both the 37 and the 40 are very much out of round with different bumps and hollows on the internal surfaces. This is to say when measuring with a inside micrometer. Yes I would agree that if you polished them up they would appear to be quite nice as I did polish one up before turning them. The thing is when you put them in a lath and dial them up you would see how far out of wack they really are to each other. I was very suprized to see the variation from one to the other in size. I can see how they could have produced very different results from one cylinder to the other if I would have used them the way they where. I am a bit of a fanatic when it comes to making everything identical from one cylinder to the other. This is why I choose to machine the bore so that they are all exactly the same. I guess I will try to use the 41.5's and hope they are not too big.

[jimf]

This is just another flaw in the manufacturing process of the carbs that makes you really wonder who the heck is making these parts. Especially when you think of the money we pay for them. The more I look into these carbs the more I am finding that needs to be fixed or replaced before I even install them. After Eljaro's discovery in the pump jet seats, thats one more thing I have to check and may have to fix. Good to know about ahead of time.....thanks for sharing all your invaluable discovery's Eljaro!

[hyper4mance2k]

Thought you night be interested in these. They are directly from Webers book.

[hyper4mance2k]

I posted those weber emulsion tubes and for some reason they were shrunk down so small they are illegibal. Anyway have any of you used annular venturi's? I have read and heard some amazing things about them unfortunetly i have only found them available for the Weber 44IDF.
http://www.cbperformance.com/Jan2000.asp
http://www.speedtalk.com/forum/viewt...01f9ee77937530

[Gaz64]

Originally Posted by hyper4mance2k

I posted those weber emulsion tubes and for some reason they were shrunk down so small they are illegibal. Anyway have any of you used annular venturi's? I have read and heard some amazing things about them unfortunetly i have only found them available for the Weber 44IDF.
http://www.cbperformance.com/Jan2000.asp
http://www.speedtalk.com/forum/viewt...01f9ee77937530

CB horizontal discharge tube is not annular.

The term "annular" refers to a ring of holes whether it be like the 650 Holley 2 Barrel that had no booster at all, or an annular booster as fitted to some Holleys, 750 DP 9379 and models 4010,4011 are examples.

Annular could be done, but it would mean a custom "tall" venturi since the annular ring needs to be inline with the main well discharge port in the carb body.

[hyper4mance2k]

I'm really interested in doing horizontal or annular discharge tubes for the 48IDA. I think they'd be a great tool for tuners out there.

[Caprimaniac]

Thanks for update, Eljaro.

Am I reading you correct: F11 tubes + 0.50 bypass works for you? No F14 or soldered F11's, then.

I have never seen the acc. pump jets dripping under idle, cold or warm, so let's say I do not have any issues there.

I will need an A/F check to see if my current setup is too lean, but- as far as gutfeelings go- the engine might run not so well now as it did with the 165/210- combo.

As far as timing is concerned; I run 14 deg @1000 rpm, 38 @ well.. 3500? Never checked closely. It's a Mallory unilite. Let's see what your timing adjustments do! Will ait for your update!

RuneS

[Eljaro]

Trying to find the culprit of an annoying hesitation above 3500 rpm , which finally was solved by correctly phasing the MSD billet distributor, I had come astray of my "good" settings on the webers.
After testing all week long I have these settings now:
40mm choke
145 main jet
150 air corrector
F14 emulsion tube
0.35 pump bypass
65 idle jet
100 idle holder
idle screw 1 turn out
21º initial advance, max 36, with a self made stop bushing.
Heavy silver springs max advance at 3200 rpm.
Car idles at 600 rpm if needed but I have it at 800. Starts without pumping the gas pedal.

Cam is a hyd.roller with 242/248 duration in a 482cid KC Pond alloy SO.

The car ran fantastically good. I hit several times 140mph (5000 rpm in 5th) with no sweat. Very smooth and snappy all the time.
Maybe the 00 bypass will remove the very slight bog if I floor the pedal suddenly below 2000 rpm but from 2000 rpm in 4th I can floor it and it just goes.
Also the idle circuit is not 100% as it will slightly hesitate below 2000 on progressive acceleration. Maybe the 00 bypass will help here too.
Definitively the F14 tube is the best, and with it the 150 air corrector gave no leaning out at WOT.

So the main circuit is now set for me, only the idle will need some working on.
I will try the 00 bypass, and it that does no do it I will try an 80 idle holder.

BTW today I used my new Avon CR66ZZ for the first time. Wow, does it improve roadholding and breaking. My old Yokohama Avid were 5 years old and rubber was probably dry, but the car never handled as good as today.
Very recomendable.

[Hans-Olof Blom]

Eljaro,

I also have a 482 engine but with a little more cam. I am running a Holley 850 DP at the moment.

I have a Weber set-up with at present 42 mm chokes. Maybe I will swith to the Webers this winter.

Is the jetting with 40 mm chokes better than the jetting with 42 mm chokes you presented earlier in this thread?

[Eljaro]

Hans,
I have not tried the 42 chokes jet. Had to sort out several variables first in order to get the 40mm chokes to work right.

[Caprimaniac]

Now I'd need some advice: If the low rpm's were to be leaned out, and you still need enough fuel at 8000 rpm and when stepping on the throttle, would the F14 or F15 be the "best" one? Both have high holes only, as I understand, but the F14 has 8,2mm and F15 8 mm outer diameter.

If the walls of the tubes are exactly same thickness, then the F14 should have a larger fuel reservoir by larger inner diameter.

The theory of capillary forces acting inside the tubes have made me wonder after reading some: Passini say the larger inner diameter makes fuel move higher inside the tubes (if I remember correctly). My own experience is that the fluid will climb higher in a smaller diameter tube. Any thoughts on this?

RuneS

[Eljaro]

I have been fine tuning my webers, especially trying to lean out the whole thing, because it was smelling too much of gas and using a lot of it..
Large main jets and idel jets are fine and make things run, because they mask any other deficiencies in the choice of air jets.
I went to smaller jets , 55 idle and 145 main and worked myself up from there.
At idle the A/F ratio came down to 13.5 on idle, but went very lean when starting to move.
So I removed the 120 idle air jet and went to a 100, which improved things a lot. I subsequently installed a self made 80 ( drilled out a 60 idle holder) idle holder air and things got in line quite well.
I noticed a slight lean hole when accelerating, so decided to open the pump Jets up from 50 to 60.Good result.
The main jets at 145 were a little too rich and power and acceleration was slightly hampered, at 13.5 to 14 A/F ratio. Since I wanted to achieve a A/F ratio of 12.8, which is for maximum power I installed a 155 main jet. The air jet is 120 and maintains the 12.8 ratio up to max rev , that is 6200 rpm.
The whole thing is slightly on the rich side, but I just thing that it has to be like that to make these engines run to its best.
Definitely Webers give these engines the crisp and inmediate response other carburetors don’t. I always had problems with Holleys sputtering when taking fast corners or when breaking hard (killing the engine in the process). Whit the Webers this is now an absolute race engine, with incredible torque and reving capabilities ( I have an aluminum flywheel) and a sound to make you absolutely happy.
I have a friend who is a Rally champion here in the Balearics( with Ford Cosworths and the like), and who had a chance to drive in McLaren F1 and several top Ferrari models. He said that the sensation of brute power and of blood draining acceleration he had in my Cobra topped anything he had driven before.
If you snap the gas pedal open from 1500-2000 rpm , first you go sideways, the back trying to overtake the front by the right side. You correct for that and there you go off like a rocket.
Fantastic sensation. You better have some good driving experience doing that or you can destroy yourself.
Anyway, my concept of supercars has changed a lot. For sheer fun I only need my Weber equipped Cobra, nothing else.