Weber jets??All who live for their triples please read this

[Synlubes]

Bill,

 

Would you have any technical docs, articles, drawings, pics other info about webers (DCOE`s mostly) you could add?

 

What book would you recommend for someone to learn and tune Webers?

[datfreak]

my chokes are a little bigger 32 vs 30- so maybe thats why mine has jets a little bigger.. Mine was dyno tuned before i got it and they had 145 mains in it!- but i had some different jets to play with and the 135 mains "felt" better..maybe that has something to do with the F2 em tubes?

I like the book "weber carburetors" by pat braden(HPBOOKS).

It has the 4 X downdraft IDA carbs that are gold plated and detailed on a chrome V8 manifold on the cover.

It has lots of old school ways to tune webers, a very interesting read even if your carbs are running perfect -just for the understanding of how the weber circuits work. And lots of pics of weber carbs that are sectioned for their inner workings.

[Nismo280zEd]

Ok, sorry i couldn't post yesterday, computer was on the blitz.

Ok, so i adjusted the butterlies or throttle plate as stated blocking the third hole (hole closesest to the intake manifold) then gently bottomed out all air mixutre jets and backed off a full turn to start with. (360, not 180).

 

Started the car, it dled too low. turned the screws out a half turn each, still a little low. turned the out another half... perfect. Idles between about 800-1000, enough to keep the engine from shaking bad. (big cam)

 

Car runs very well, except top end i have backfire when i shift, and when going at steady speed say 40mph in 4th carbs will "click" but not backfire, is this a normal thing? (webers are still new to me ) this is when the car is at temp i should mention so it's not from being cold.

 

One other thing i wanted to ask, what degree of adnvace are you guys running? I've been playing with it, i've got it about 20 riight now seems really smooth there.

 

-Ed

[Drax240z]

Timing depends a lot on the specific qualities of the engine, however, mildly build L-series engines seem to respond well to 10-14* initial, and around 36-38* total. In my experience only the (low compression) turbo engines really work well with 20* or more initial timing.

 

Try backing off your timing to 12* initial. (with vaccuum advance disconnected) Varify that as you rev the engine the timing is advancing, you should be at about 36* advance at ~3000rpm.

[zredbaron]

here i was, thinking i was going to start a good thread again, but NO! datfreak already beat me to it!

 

so...this is my 3.1 L28 setup, and here's how it runs.....

 

i am running the 40dcoes, and here is my current setup:

 

34mm chokes (main venturis)

180 air correcion jet

55.F8 idle jet

130 main jet

F11 emulsion tube

 

my mixture screws are happiest 3.5 turns out from bottom, and the idle speed screws are about 3/8 of a turn past contact with the fuel lever....spring....mechanism....thing. haha.

 

currently, my car dives if i try to transition between very light pedal and more pedal. the hesitation passes, and the car picks up accelleration a moment later. above 3000 rpm this is not a problem.

 

i am under the impression this is a problem with my idle circuit being too small. can anyone positively confirm this for me? some say its the idle circuit, but NapaBill says throttle plates....?

 

 

according to a website i found online, (http://members.aol.com/dvandrews/webers.htm) i can calculate all the jet sizes i need based on the main venturi size and cylinder displacement. here are the numbers i got from this calculation.

 

34mm chokes (main venturis)

185 air correcion jet

135 main jet

F2 emulsion tube

60.F8 idle jet

(f13? f8? f9? here's what it said about the Fs:)

Weaker Normal Rich

F3 , F1 , F7 , F5 ,F2-F4 ,F13 ,F8-F11-F14,F9 , F12 , F6

 

 

can anyone confirm or deny these calculations in their 3.1L?

 

also, i have been told that 34mm main venturis might be too big, that 32mm might be more appropriate, since smaller venturis allow better atomization when not at peak horsepower. the car is to be autocrossed...

 

and one more question, how much will porting/camshaft selection affect the jetting requirements? the cam i am using has .525 lift and has power from 3500 - 7200 rpm. my head's intakes flow 200 cfm (from sunbelt, which they say is 225 cfm by anyone else's flowbench). e31 head, av gas.

 

no, i dont know the power, yet. just put it on. ill post that to my old thread when i dyno it. it may be a few weeks, but it better not be!

 

as usual, your infinite experience is always appreciated....

[Drax240z]

The 3.1L we just build REALLY responded positively to the switch from 32mm to 36mm chokes. Plenty of bottom end (much more than the 2.8L with 32mm) and of course top end gains as well.

 

We're going to be mucking some more with the jetting on this car once we have our wideband. (end of the month) I'll try to remember to post the results to this thread.

[Nismo280zEd]

car has been running well still, still have clicking in the carbs but that could be due to vacumn leak and adnvaced timing. Will retard to about 12 and try that after i get my new gasket.

-Ed

[zredbaron]

clicking? can you describe it in more detail?

 

if it can be described as mettalic rattling, then you might be hearing detonation....

[Guest NapaBill]

Doug,

I don't have hardly any Weber stuff left, other than some jet drills, special tools, and a 40IDA3C three-barrel that I mounted to a walnut base and use as a pencil holder!

The only book on Webers anyone would ever need used to be called, "Technical Introduction to Weber Carburetors" and was published by Weber. It appears to still be available under the title "Weber Factory Manua" from http://www.webercarbsdirect.com/inc/pdetail?v=1&pid=635 for $19.95.

 

RedBaron,

Just remember, that sequence of F-#'s only applies to emulsion tubes, NOT to the F-# on idle jets where the smaller the F-# the richer the upper end of the idle/transition circuit.

[Nismo280zEd]

ok here is the exact sound... push open the thottle and let it go... the butterly slams shut... makes a "click" noise. so i suspect it's backfire through the intake. gonna retard the timing a lil and let ya know hwo it works.

-Ed

[DeusEx]

Oh thank God,

 

This thread is straigh from god i put a lumpier cam in over the weekend and noticed that at high RPM it seems to starve for fuel a little, my local Motorsport shop told me i need to replace my main jets and maybe air correction jets to get the most out of it. At a high $$ might i add. So i stumbled on this forum, should save myself some cash hopfully.

 

Im running Triple 45mm webers (im not that technical so please excuse me if i dont have all the tech details, assume they are standard i guess).

32mm Venturis

so i guess i have..128 Main Jets and 178 air correctors

272 cam with 318 (cam only) duration

L28 with flattops (2.9)

Ported and Polished P90

2.5 Exhaust

 

If anyone could give me a rough idea that would be great otherwise, ive printed out this thread and shall sit down with my mechanic friend and we shall work out the details. Also, is there really any advantage to getting larger venturies, as these are quite expensive

 

Now since its starving alittle for fuel up top (well surging is more the word) does this mean i require larger air correctors or main jets?

 

And where can i find the (please forgive me if its a stupid question) emulsion tube size, as from what ive read, changing this has some benifits.

 

Thanks

[Guest NapaBill]

DeusEx,

You can probably find what you need in this thread. You better re-check your jet sizes though, Weber jets come in incrememnts of 5/100's of a millimeter, thus 1.00, 1.05, 1.10, 1.15, etc. Commonly referred to as 100, 105, 110, 115 and so on. So unless somebody drilled your jets to non-standard sizes, you don't have 128 mains and 178 air correctors.

 

Once you sort that out, the thing to change to fix leaness at high rpm is to go smaller on the air correction. If you enlarge the main jets you will richen the entire main circuit from 3500 rpm up. Also, you usually want to change air correctors by a factor of three compared to main jets. In other words, if it would take an increase from 125 to 130 on the mains to get there, you would reduce the air correctors from, say, 200 to 185 to get the same incremental change.

 

You could also swap emulsion tubes, but that is a lot trickier and more expensive.

 

Good luck,

Bill

[DeusEx]

Thanks Bill,

 

With regards to the figures, i havnt measured them i just used the formula (venturi*4 for mains and then +50 for air correctors).

 

I agree everything i need to know is probably in the thread and it is awesome in its details. I understand that new Air corectors give the top power, but thanks for pointing out that i need smaller ones. So if changing the air correctors will give me more smoothness and power delivery up top, and mains will give more throughout, is there any point in changing both, or will i need one or the other?

 

SOrry if this is a stupid question.

 

Thanks heaps

[Guest NapaBill]

DeusEx,

No problem.

The basic idea is that if you are lean all the way through the operating range of the main circuit, you enlarge the main jets. If you are lean only at the top end, and mid-range down is all right, you go to smaller air correctors, which mainly affect the higher rpm range. In other words, if the mid-range isn't broke, don't bother fixing it!

 

Besides, never change two variables at once, since you won't know which change made the difference.

 

As to the size, the jets have their size stamped into them. Always a good idea to double check though, in case some bugger got in there with a drill before you had them. Just remember to always use the smooth, butt end of a drill to check size so that you don't accidentally score or scrape the jet with the fluted end.

 

Some people (mainly those in the business of selling jets) will tell you that drilling them does not give the same flow charactereistics as factory sizing. I asked Luigi Potenza from the Weber factory about that many years ago and he said, "Yeah. We use different drills than the ones we sell you. Sure."

 

Bill

[DeusEx]

Thanks Bill, you just condensed two pages of info into one post, i think you deserve a medal for that is there any set guide for how much less i should decrease my air controllers by? say they are 180, should i take them down to 170? 165? 160? Is there a set number that is looked upon as ideal for top end? Its Hard to tell how im running in the midrange, as when the cam is off powerband its chuggy, and not at all smooth (unsure if this means tune the carbs or thats the way of the cam) and once it starts to rev, it gets the surge/stutter maybe around 5-6k. Hard to tell without the tacho.

 

And will replacing these items put the carbs out of tune? Ie, can i just throw on the new Air correctors, and drive it? or will it require a tune?

 

Thanks again

[Guest NapaBill]

DeusEx,

There is no way someone sitting on his couch the other end of the world can tell you exactly what your motor needs, especially with mods like cams, headers, etc. What you really need is a chassis dyno and a good tuner.

 

As I mentioned earlier though, if it seems like a change of one size on the mains would do the trick, then go three steps on the airs to get the same increment. From 215 to 200 on air correction will get about the same incremental change as 130 to 135 on the main jets.

 

You can also rearrange your mid to high mixture by changing emulsion tubes, but as noted in earlier posts you really have to sit down and study the blueprints to figure them out. I would say that F-16 or F11 e-tubes would probably work well for a gasoline burning, street driven, under 7500 rpm engine of 400-500 cc's per cylinder (hows that for a qualified statement?), although most of them can be made to work. If you have F-2's (which were for methanol), definitely change them.

 

As for the chugginess, look back through my earlier posts about setting the throttle plates and how the idle, main and progression circuits work.

 

Ciao!

Bill

[Guest NapaBill]

Sorry, I missed one of your points. Changing the air correctors will not require any other adjustments or tuning.

[DeusEx]

You right its very hard to assume and tell what people want without ever seeing the car. After reading alot ive compared the specs of other peoples cars to mind, and the settings im running, theoretically should be fine, but as i said, i worked out the Main Jets and air correctors from the formula, i havent actually measured them. But i guess reducing the size of the air corrector would be a good start.

 

I do have access to a very good tuning place, but in order to save money and gain some knowledge i thought id attempt it myself. I will give the air correctors a shot as they are not overly expensive.

 

Thanks for all your help, ill see if i can get some results.

[zredbaron]

Again, this was my setup with 40DCOES (3.1L):

 

34mm chokes (main venturis)

180 air correcion jet

55.F8 idle jet

130 main jet

F11 emulsion tube

 

I swapped my idle jet to 65.F8 and the car is A LOT more driveable. It still isn't perfect, but transitioning between little pedal and a lot of pedal isn't nearly as picky.

[DeusEx]

OK,

 

Well i pulled my jets apart last night to find that the previous owner had worked more of his strange mojo.

 

i Now have

 

200 Air correctors

F16 Emulsion

120 Mains

 

Instead of the theoretical 180, F11, 130. So it looks like this is really a down low power setup (Of which my car had plenty before the new cam).

 

I gave them a good cleaning with carby cleaner, and it drive much better now. But it isnt great. The local tuning shop refused to give me advice (hows that for client service) on what jets would make the improvement. There are a number of setups that you guys have that i would like to have tried, but i think ill just have to give it to the tuning shop and let them do it.

 

Oh well, at least i learnt alot in the process, so much for saving money. I also installed a new tacho for the MSD, and it seems that my peak power is somewhere around 5,500 - 6,500. Probably in the middle. The fuel lag/surge occurs at around 5, and the cam starts pulling at 4,500. Needs to be coaxed to keep reving.

 

Thanks again