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

[zredbaron]

lots of questions, many of which are incomplete.

 

the term ticking has to be defined. you have to *find* where its coming from. is something loose and rattling? is the engine knocking (which can sound like loose marbles under load)?

 

in the case of knocking, try retarding your ignition a little to see if the noise goes away. i doubt that your compression is high enough to warrant higher octane than 91. are you using 87?

 

55 idles are too big for you. i have a 3.1 with a full race cam that idles at 1500 and i use 55-60 depending on the season. richening up the idle circuit (no such thing as the transition circuit), may feel smoother up to a point, but it will actually make less power/torque. i find that in my car, the pedal becomes overly sensitive when the circuit is just right. for you, i would think 45-50 depending on the time of year.

 

to test out a good starting point for driving, try turning all of your mixture screws all the way in, then backing them out 1 and 1/2 turns. then richen or lean all of them by 1/2 turn increments. if, when you go richer, the engine idles at a higher rpm, then you *might* want to put the next size idles in (i say might because you *might* be on the fence). and vice versa. this is a starting point, so you must road test with various throttle positions in the 1000-2250 rpm range. (after this rpm the idle circuit is no longer in use)

 

your venturis are too big, too. your car is having a hard time at low rpm because your engine simply isn't drawing in enough air until higher rpms. i would recommend 32 mm for you, based on the charts in my weber book. yes, you WILL make more power (wider, stronger, smoother power band) if you put in a smaller venturi for your application.

 

if and when you spend A LOT of money on a VERY GOOD head job and cam, then i'd go with 34s, maybe 36s depending on how your car is used (34 for street use). save the 36s for the stroker.

 

you have to have the chokes fully open to idle at 1000? if that were true, then you couldnt accellerate because the pedal was already floored. are you sure that you've found the idle speed screws? they will be immediately to the side of where your linkage attaches to your carbs.

 

you have to start all of this KNOWING that the carbs are synched on the linkage side. if they are not, then you are wasting your time. get a good flowmeter (like the one top end performance sells) for about $40. back ALL of your idle speed screws out, then hold your pedal at a constant 2500-3000 rpm. then adjust your linkage until they are all matched, and tighten them. MEASURE THEM AFTER YOUVE TIGHTENED, as sometimes it gets thrown off. be precise.

 

then, you can tinker with the jets, and mixture and idle screws.

 

to be frank, you haven't read much about webers at all. perhaps you have been reading peoples opinions. what you need is the book called Weber Carburetors (HPBooks). I found mine at a local barnes and noble. that will detail the relationships between jets, circuits, and will detail how to tune them.

 

one last thing, don't over tighten the bolts between your manifold and carbs, or you will get fuel leaks. they might seem loose, but the washer is actually a spring. it isn't meant to be tightened until it is completely flush. tighten them until the spring washer collapses just a tad more than half way.

 

good luck!

[Lazeum]

First of all thanks for the time both of you, you took to answer

 

I've got 2 books that I've read twice. Obviously I'm going to read them again for sure (even without your comments ). I've got "Weber Carburators" from HPBooks as well as the Weber Tuning Manual.

 

For the knock, I've tried to retard the timing and see if it was making a difference. It made a small difference but it did not help as much as expected. I went to a point where retarding the timing again was making the engine running very bad.

 

Your comments regarding how the bolt should be tighten is interesting. I did not overtighten them but for sure I compressed completely the spring washers.

I do not understand though how I can have fuel leak if I overtighten the nuts.

 

I have many different idle jets available. 45, 50, 55 F9. I will backup to the 50F9 if you, guys, say 55 is too big. At least to go back to where it was before, when the engine was running ok.

 

How can the idle drop that much between before and after knowing that I've just changed the idle jets and tightened the nuts?

I don't think the idle jet should create such a difference, especially since those are supposed to help fuel flow through the transistion holes (=no effect at idle?).

Regarding how the nuts are tightened, if there were no leak before, since I've clamped the carbs "better", we should see no difference.

 

I take good notes of your comment regarding venturi but I will focus first on having the car running smoothly prior to mess up with HP.

 

The problem is still maybe besides the engine. I've tried to spot exhaust leak with no luck (with a fuel hose "plugged" in my ear to spot air flow around connections)

 

One more point, I've changed the air filters. I went from a ITG foam box to 3 K&N but this should not change anything.

 

It would be better then to say that "there is a rattling noise under the hood."

The head has been reworked a little as well but I don't know exactly what (polished, valve job?)

Last point, regarding gas, I'm using 93 octane fuel

[Lazeum]

you have to have the chokes fully open to idle at 1000? if that were true, then you couldnt accellerate because the pedal was already floored. are you sure that you've found the idle speed screws? they will be immediately to the side of where your linkage attaches to your carbs.

 

I'm not following you regarding the chokes.

 

I can rev the engine quite ok with the choke fully on.

 

According to what I've understood, the throttle are not open because of the choke. The choke seems to only inject gas to richen the mixture when the engine is cold (i.e. to compensate air/fuel condensation)

To fully open the choke would tell me that the air/fuel mix is way too lean with my condition.

 

Regarding the idle mixture screw, I believe it is the only one with a spring (very close to the intake manifold)

Idle speed screw, it seems to be the same bolt as the one we use to synchronize carbs.

 

Anyway, I haven't messed up with those yet.Until I'm not confident about what to do, I don't do

[Zmanco]

How can the idle drop that much between before and after knowing that I've just changed the idle jets and tightened the nuts?

I don't think the idle jet should create such a difference, especially since those are supposed to help fuel flow through the transistion holes (=no effect at idle?).

Huh? You put larger idle jets in and now your engine is idling slower and smells bad - both symptoms of being too rich. I don't understand the basis for your question?

 

As for cold start chokes, just leave them open and forget about them. I was able to start on 20 degree F days in Colorado without them just fine. The reality is that once you get the webers dialed in, you'll find they are always on the rich side - they will deliver the best performance and drivability when tuned that way. The cold start chokes will just be a distraction for you. If you get the warm temp setup dialed in and THEN you find that you need help with cold starts, only then begin to mess with them. You've got enough to work with right now

[Lazeum]

Huh? You put larger idle jets in and now your engine is idling slower and smells bad - both symptoms of being too rich. I don't understand the basis for your question?

 

you're right, this looks like rich condition but should I see the rev going higher as soon as I open the choke? I would think the car should "suffocate" and run slower.

I'm wondering if it could also be because of the "cold" start. I pressed 2-3 times on the throttle pedal prior to start the car.

I'll back off to the previous settings and see how it goes.

[zredbaron]

I'm not following you regarding the chokes.

 

I can rev the engine quite ok with the choke fully on.

 

I had assumed that by "choke fully on" you were mis-speaking and really meant the throttle plates were wide open (which would break your engine if not under load). my mistake.

 

as for the HPBooks Weber book (published 1988)

at a minimum, read pages 34-43, 99.

lots of good info in 115-135 (modifications chapter). big picture concepts help you realize what you're asking your engine to do and why. there's more to it than simply increase jet size to richen.

 

you can cause fuel leaks by overtightening very easily because of what is in between your carbs and your manifold. each manifold runner has a piece of plastic sandwiched between two rubber o-rings. thats it. if you tighten too hard, you will damage the o-rings or crack the plastic or both. also, don't replace those o-rings with any old o-rings. they are specifically designed to handle fuel and not deteriorate.

 

the design is for this 'gasket' to absorb vibrations AND keep a good seal in both low temps (winter startup) and high heat (fully warmed up). its a very good design, but not foolproof.

 

with regard to the idle jets, the weber book details the following. you are correct, they do not affect idle mixture as the name would indicate. the mixture screws do. thats what the books says. however, the book also says that fuel doesn't go through the main circuit until above a certain rpm. so, until then, fuel is drawn through some very small cored passageways that cannot be adjusted, but DO need the throttle plate to be in the right spot. the adjustment, is the needle at the bottom of the mixture screw, which determines how much fuel is allowed to spray into the carb with the throttle plates closed.

 

thats the theory. the fact of the matter is, in practice, if i tune my car to idle smoothly then change my idle jets, i will absolutely have to re-tune my mixture screws to find out where the engine wants it.

 

the reason is, the throttle plates arent completely closed. they're ALMOST closed! when they are closed, its all mixture screws and cored passageways. however, when you use the idle screws to set the right rpm (900-1000 with a decent street cam, don't remember stock sorry), you are opening the throttle plates a very slight amount, and this is why the idle circuit is in use, which is why it affects idle. fuel is being drawn through BOTH the cored passageways/mixture screws AND the idle jets. the mixture screws then allow you to refine where your idle jets put you. make sense?

 

According to what I've understood, the throttle are not open because of the choke. The choke seems to only inject gas to richen the mixture when the engine is cold (i.e. to compensate air/fuel condensation)

To fully open the choke would tell me that the air/fuel mix is way too lean with my condition.

 

Regarding the idle mixture screw, I believe it is the only one with a spring (very close to the intake manifold)

Idle speed screw, it seems to be the same bolt as the one we use to synchronize carbs.

 

oh, i get it. you literally mean the chokes used for richening to warm up the car. i forgot we even have those! lol. again, this is why i hate calling venturis chokes. they're venturis!

 

don't ever use the chokes when tuning your car. the chokes have their own circuit entirely, as the weber book refers to them as a "carburetor within a carburator." they are disconnected on my car, and are always shut via their spring. for street use, it's a good idea to use them to warm up the car. a very good idea.

 

yes, the mixture screws have screws and are fairly close to the manifold. one per barrel / cylinder. you'll know youve got the right ones if, while the engine is at idle, if you screw them all the way in, the engine dies. you want to screw them all in to the bottom, then back them out exactly 1.5 turns. thats a starting point. increase/decrease by 1/2 turns and ultimately 1/4 turns to figure out what the engine likes the most (highest rpm and smoothest). then back down the idle speed screws to get the right rpm.

 

the idle speed screws are one per linkage arm (therefore one per carb). located on the side of the carb.

 

don't ever tune your engine until it has fully reached normal operating temperature. likewise, don't tune it if the engine is hotter than normal, either (carb/manifold temp... as somewhat indicated by water temp).

 

it matters.

 

also, taking a look at your jet sizes again, your mains might be too small for use with the 36mm chokes (again, i recommend 32 for you). as a *starting point* the rule of thumb for mains are venturi size x 4. in this case, 36x4= 144, so perhaps 140 or 145 mains would be better. more air from the venturis means more fuel needed. problem is, your head/cam can't flow that much volume, so you can't use all that it's trying to send. 140 is probably a good starter.

 

that said, *again*, i'd like to see you with 32mm venturis, which would be about 130 mains for starters. understand that the 140 estimate is to match the venturi, not your engine. it's helping it run better, not best!

 

air correctors rule of thumb is mains + 60, but i find this a bit too much for our cars. i've also found that the more upgrades i do, the smaller the difference between mains and airs gets. i bet 185-190 would work for starters. i use increments of 10 when messing with air correctors (5 for mains of course). air correctors don't kick in until above 4000 rpm. or so. ish. (depends on engine and other things i know nothing about.)

 

what jets do you have avail? i have a large set, and after my upgrades, many are no longer useable for me. if you or anyone is interested, send me a private message so i don't hijack the intent of this thread.

 

and you're quite welcome, lazeum. it's taken me 10 years to feel like i at least have an idea of what i'm doing with the webers. i have yet to meet an expert and watch what they do. it truly is a lost art, so stabbing around in the dark eventually yields a limited amount of experience, especially when you go back to re-read chapters you've already read. *cough!*

[zredbaron]

http://www.teglerizer.com/dcoe/rasorcom.htm

 

i just re-found this link. lots of great diagrams that the weber book doesnt have. this explains the idle circuit, and looking at the pics, looks like the fuel ALWAYS goes through the idle jets, even when the throttle plates are closed. i thought it had two separate cored passageways.

 

a picture is worth a thousand words!

[josh817]

Ok this kinda of frightens me to think about... For our triple Weber's to be jetted correctly, its like a good $100 worth of jets.

 

To be able to test and find the proper jets you need a collection of jets, which is even more money. Am I wrong to assume that you need a good $250 worth of jets to just tinker? How much do you have invested for your set Zredbaron? I have a box of jets but if you find the proper ones, multiple by 3 for each carb. This sucks to get started, once you have everything I'm sure its fine. :[

[zredbaron]

yeah its not cheap. as much as it pains me to admit it, i'd say after venturis and jets, i've probably invested a little over $1000. again, this is after 10 yrs and about 3 separate rounds of engine upgrades.

 

each round of upgrades results in the need for a new set of jets to play with, +/- an adjustment on each (idle, main, air corrector).

 

if i ever do go to the 45dcoes, i'll likely have to rinse and repeat a few more times. looking forward to it.

[josh817]

My problem with this is I don't see how after all of that you don't have a big enough collection to say "ok let get our box of jets and pick... this one" rather than always buying more.

 

Its just now hitting me as I know ITB's are cool and you adjust them by a click of a mouse. :/ They are rather expensive too... I think my Webers may be up for sale in a short amount of time because it all. As much as I HATE electronic stuff and trouble shooting it, I think it may be in my best interest to do it...

 

 

A sad moment of realization...

[Lazeum]

zredbaron,

I've spend the rest of my Sunday reading Weber books.

I do understand what you meant regarding how the idle circuit works. I thought fuel would go through the idle jet with no interference, this is not true.

I have seen as well how the rubber joint are supposed to do (decoupling). However, I'm still wondering if there were some leaks in the system. To go back to the previous setup will confirm or not if there were any.

 

The first thing I've done on the Z afterwards was to check where I was as far a mixture screw setup. I found that some screws are 1 1/2 turn from being close, some others are 2 1/2 turns. None of them is set up the same way.

The weber are quite old but they have been rebuilt by a professional 2 years ago. Transistion port are seals with caps which is a shame, it makes the throttle plate adjustment difficult to check but the rebuild job has been done properly, I would assume everything should be fine.

 

I would have also to double check the venturis size as well. I believe they are 36mm but I might have said something wrong. It is hard to read. I do also have spares with 30mm ID.

 

Regarding your offer for jets, that's super nice from you but I'm far away from you now. I went back to Europe (France).

 

I have a wideband available, I believe it would be a helpful tool in my process.

We always say we are learning by our mistakes. I can garantee you that I'm learning a lot. Hopefully in less than 10 yrs I'll be wise enough to understand the webers (then I shall be able to turbocharge the car with those )

 

Josh, I've seen your build (very nice). I would stick with Webers, your engine would not have the same soul without those. Of course, there is money involved, it's your choice but you should think twice

[zredbaron]

My problem with this is I don't see how after all of that you don't have a big enough collection to say "ok let get our box of jets and pick... this one" rather than always buying more.

 

Its just now hitting me as I know ITB's are cool and you adjust them by a click of a mouse. :/ They are rather expensive too... I think my Webers may be up for sale in a short amount of time because it all. As much as I HATE electronic stuff and trouble shooting it, I think it may be in my best interest to do it...

 

 

A sad moment of realization...

 

 

well, i do have this collection in any reasonable sense. the problem is upgrades. if you follow the mains alone, the stock L24 used 125s i think, my poorly running 3.1 used 135-140s, my new head and high perf cam used 155 or so, and my forged pistons/race compression/race cam uses 160-165. that's four different rounds. not to mention i've gone through 3 rounds of venturis.

 

shelling out $150 for tuning is very, very cheap horsepower. negligible by comparison of the upgrades that took you there. your ITB setup will cost $5k. $3k for the ITBs, and $2k for a computer to control it.

 

if you want cheap horsepower, turbo or small block are definitely the way to go.

 

also, i seem to be maximizing the performance (ie at the upper flow limit) of the 40dcoe with 36mm venturis, and i have found curious results. i want to prove this at a dyno shop sometime, but i'm running 160-165 mains and 185-190 air correctors. not the usual difference.

 

this oddity has caused me to unknowingly purchase in the wrong direction.

 

fuel selection also matters. i'm running 100 octane and i'm about to switch to 109.

 

tempurature, elevation (specifically barometric pressure), humidity, fuel selection and timing all play significant roles in your mixture and subsequent burn rates.

 

 

lazeum, you have to physically remove the venturis to see the number stamped on them. it's very easy to do (just look in the dcoe section in your book). i wouldn't go any further until you find out what youre starting with.

 

a wideband is a very useful tool. i use one myself.

[Zmanco]

I have seen as well how the rubber joint are supposed to do (decoupling). However, I'm still wondering if there were some leaks in the system. To go back to the previous setup will confirm or not if there were any.

A simple way to check for vacuum leaks is to spray carb cleaner on the questionable areas with the engine idling. If the idle speed changes you've found a leak.

[josh817]

A simple way to check for vacuum leaks is to spray carb cleaner on the questionable areas with the engine idling. If the idle speed changes you've found a leak.

 

Exactly what my dad told me.

 

I think I'm just being frightened by all this stuff. I'm looking at it like a calculus problem where you have this but you need that and there are several ways to get there. As in like you COULD change your main jet but the better way is to do this. Just made that up off the top of my head... I am kind of disappointed with 40's and I think if I were to make a change it would either be ITB's or 45mm so I know I can just choke them down a bunch if needed. I'm consulting 1 Fast Z after doing a search this morning on ITB's and saw that instead of running Mikuni motorcycle carbs which still use jets, perhaps I use crotch rocket TB's. Its all a possibility. I may be stuck with carbs forever though because if I remember correctly from the turbo motor I pulled a ton of sensors. If I all of a sudden need these again then its too late since I built it for the purpose of ridding them. My general understanding on price is I don't need a manifold or a fancy computer. I thought MS did FI only systems... I'll do some research and leave this thread for CARBURETORS since thats what it was meant for.

 

K so what I'm noticing (not going to do anything just yet) is that when I blip the throttle say 40+% it bogs down and then comes up. If I do it gently it comes right up. I think the lower band is suffering. Even when I'm in gear and rpm's get below 2k if you floor it the motor just chokes all over itself and sound like crap until you hit 3k. I haven't set my advance at all because Dad is saying 30º+ is hefty for the motors he builds but he doesn't do Datsun motors so he is most likely wrong seeing from everyone elses results. Thats my situation, just sharing not really asking as I haven't ventured into the depths of this thread just yet. Everyone posted their problems as soon as this came up so I'm sure its in here somewhere.

[Careless]

sounds like too much fuel spraying from the carbs at WOT if you're down low and gun it.

[Lazeum]

This weekend I went back to 50F9, the car idles ok (that was expected from the discussion we had last week)

It is rough, I suspect the idle mixture screws to be NOK. I'll see that later.

 

I made sure as well the carbs were not overtorqued on the intake manifold. I've tightened all the bolts ok, then remove 1 turn out on each bolt.

After a trial, the ticking noise is much less present than before but it still barely exists.

I've just checked advance at idle (900rpm), I am around 9-10º of advance. It is not optimized but it is good enough to beleive timing does not create any problem. (no check at 3000rpm as I should have => no tack and by myself to do it)

 

I have to take care of legal issue with the car right now (she's not street legal anymore at the end of the week because of turning light colors and hand brake). I'll let you know how everything is doing... Next step will be with a wideband.

I should be able to see more precisely what is going on, especially at acceleration.

 

 

People say we are learning from our mistakes, I'm definitely learning.

Thanks guys for your help

[akumazeto]

I have a question and I badly need help. Everytime i go over 2000 rpms it studders. This guy gave me what i need for my tripple set up but I need your guys opinion on this. By the way Im new to the forums.

 

130 main

160 air

 

then he wrote this that I need.

145 accell

55 bleed

 

But i went to the store and they dont understand the terminology of this. Plus I asked for 50f9 cause thats on the list they said they never heard of that number.

Can someone please help me im stuck!!!!

[zredbaron]

akumazeto,

 

no one has replied yet because you aren't helping us help you.

 

what kind of motor do you have? displacement? cam? mods? application? which carbs!?! venturi size? if you have read this thread at all, you would already know that you can't be advised without this information.

 

second, either this guy is confusing your carb with another or you didn't interpret his instructions correctly.

 

the main and airs *might* be a reasonable starting place *if* we knew your application.

 

however, the other two don't exist in our weber dcoes. this *is* the kind of carb you're using, right?

 

the only thing i can think of by 'accell' is that he means the pump jet, but those are usually around the 40 range. not 140...

 

i have no idea what he wants or means by 'bleed'

 

so again, you have no responses because no one has any idea how to help you. you might as well have asked an art instructor why you cant take the square root of a word. it just invokes the word "HUH!?"

 

... which is the response the shop gave you when you asked for these jets. however, if you asked for 50f9 idle jets and they don't know what that is, then call a different shop. i've got some in my tackle box.

 

so by all means, get back to us with your application, and you'll likely get some advice.

[akumazeto]

Sorry about that. Yeah i was not thinking of that. I have a 73 240z with a 78 l28 engine. tripple weber carbs cannon manifold.no cam its stock.

I checked my jets i am running

160 air

f11

130 jets

idle jets are 50f9

28 chokes

 

after 2000 rpms it studders alittle and my spark plugs from the firewall to the 4th spark plug is black. I just changed them out so i know they are new.

 

I turned the ilde screws 1 1/2 turn. but seems im still running rich or lean.

Can anyone tell me what I can do to make my car runn better. It idles at 900 rpms so that is good.

 

Again everyone sorry for not being specific. I'm new here

[zredbaron]

your jets seem like reasonable starting points. you might *try* running a slightly leaner idle jet (smaller). that may or may not help your studder. again, experimentation is ALWAYS in order. if i had to offer a wild guess, i'd say try 135 mains and 175 airs and see how it likes that. but again, its a WAG.

 

as for your 1.5 turns, did you tighten them or loosen them? that's a pretty big change. usually 1/4 turn can noticeably affect the idle. (also, have you counted the number of turns it takes to tighten them to the bottom seat, and averaging this number and backing them all out to be the same? this *could* be the cause of your fouled plugs)

 

no need to apologize for being new. unfortunately, i don't see anything that blatantly jumps out (maybe someone else does?), so it seems youll just have to start experimenting! if you buy one size smaller and one size larger of each jet, then you can have yourself a good tuning experiment. you might be able to benefit from bumping up your venturis (aka chokes) up to a 30 or 32, but doing so would require new idles, mains and airs.

 

 

 

i'd probably say the biggest complaint/trend that i've heard across the board is studder/hesitation until about 2500-3500 rpm or so (variance depends on cam i suspect). i have this hesitation, too. throughout my car's history, below that magic rpm i have to throttle the carbs just right (ie dont floor it, but finesse it) to get the best accelleration.

 

i have two theories for this, and i intend to test both via my butt dyno and a chassis dyno within the next 4-6 weeks. #1: vacuum advance and #2: emulsion tubes.

 

1) i don't know about you or anyone else that complains of this hesitation, but my iginition does not yet incorporate a vacuum advance. optimal driveability and power is obtained by varying advance based on engine load (measured by manifold vacuum). most cars accomplish this by a vacuum line running to the distributor. i don't yet have a MAP sensor for my direct ignition. its possible that timing has been partially responsible for my hesitation.

 

2) based on reading about our dcoes, i've always thought that our application is been on the fence between the f11 and f2 emulsion tubes, and that perhaps the higher performance L6s could benefit from the switch to the f2.

 

like i said, i'm going to test these both very soon, but i'd love to hear anyone's thoughts or experience. anyone have any input?