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

[yetterben]

really dude i have read the whole thread months ago. I am telling you what worked for me and several other webers i have setup. Your narrow band tells you nothing absolutely nothing. Not trying to be combative but you gotta ditch that thing.

 

Saying you dont want to buy one cause it does not match the other gauges is kinda silly. Aem makes a very good unit sub 200 bucks and its responsive as hell.

 

Hell i am even running boost threw my triples now and i can punch it at 800 rpm and it takes off like a mutha. You need a wideband spending money on jets for trial and error is well error.

 

If i can tune a blow through weber setup to be perfectly linear than N/A should not be a issue. I dont seem to understand why so many people are having such a issue. If the progression ports are setup fine and the idle is setup fine there should not be a stumble. How do you know your overly rich? You have no data to back this up other than a setup that can read 0-1volts

Edited April 26, 2010 by yetterben

[yetterben]

Every stumble i have ever encountered in triples is because of a lean spot not a rich spot. Your theory of bigger cam etc etc would make the rich factor negate itself. How could you be so rich if you dont have enough vacuum to pull the fuel from the carb. Air moves faster than fuel hence the progression ports and circuit. I dont think you have enough air volume at say 1,400 to draw that much fuel out of the ports to be that rich.

 

I set mine up at 11 for afrs steady so that when the tip in occurs its getting into the 12 but buy the time it get to high 12s i can watch on my wideband where the main circuit is coming on. It slowly goes back down in a liner fashion too the 11's. When it was N/A i had the idle set to the 10's. At first i had it at 12.7 but i had issues between idle and main circuit. So i plopped in a bigger idle. Backed the screws out 1/2 turn got my idle at 10.5 or so and the stumble went away.

Edited April 26, 2010 by yetterben

[cygnusx1]

When you snap the throttle open from low revs and high loads, your vacuum pretty much goes away.  Without vacuum, there is no way for a carb to deliver fuel.  That's the job of the mechanical accelerator pump.  The pump will deliver fuel under the exact conditions that most people observe a flat spot.  There are so many documents out there to tune webers but here is what I have learned from experience and from digesting everything I have ever read.

 

Tuning a DCOE is as follows:

 

 

 

 

KNOW THE BEAST

 Write down all the specs of your carbs.

 

Model

Choke size

Aux venturi

Idle Jets

Main Jet

Emulsion Tube

Air Corrector

Pump Jet

Pump bleed jet

FUEL PRESSURE - 3psi   < I filled this one in for you.  Make it that.

Needle valves

 

 

 

 

THROTTLE PLATE POSITION

 Mechanically establish the throttle plates, all identically, just downstream of the progression ports. You can do this by looking through the progression holes with a light. (future angle adjustments should be limited to +/- 1/4 turn on the stop screws from here on and in the future for idle tuning) 

 

 

 

 

WATER IN THE POOL

 Float levels (CRITICAL) measure the fuel level in the bowls.  Take out a main jet stack and measure the fuel level.  Should be 25mm from the top of the main jet hole. This affects transition greatly! higher levels = earlier mains.

 

 

MIXTURE SCREWS?

 Turn the idle mixture volume screws out to the spec for your carb model. These screws don't mix fuel and air.  They are controlling how much premix of air fuel is going to the engine at idle.

 

 

 

BEST LEAN IDLE

 Establish idle speed by iterating adjustments in the following; Mixture screws/+- 1/4 turn on the throttle stop screw/ignition advance-retard. Repeat over and over to get best lean idle (I do it by ear turn each mix screw in SLOWLY until the motor roughens and come back out SMOOTHLY until it smooths out again).  Then turn all the mix screws out(rich) 1/4 turn if you get popping on decel later. (helps reduce lean pop during decel)  Stay within the specified TURNS for your carb.  If you need to open them up too much, you need a larger idle jet.  This is critical to understand because the idle jet is also feeding the non-adjustable PROGRESSION PORTS.  If the idle jets are too small or too large, you will get bad progression off idle. REMEMBER ONLY!!> +- 1/4 turn on the throttle stop screw.  If you can't get it in that range, you have other issues like vacuum leaks and/or too much timing. If your timing is too retarded the motor want to idle slower, forcing you to open the throttle stops.  This exposes the progression ports and renders them useless for progression.  Fell free to use more ignition timing to keep your progression ports COVERED!

 

 

 

TEST DRIVING

 Establish proper main circuit to get good AFR's and drive-ability from 2500rpm and up. This is where a wideband is priceless.  Experiment with slow throttle movements and focus on steady state and power smoothness above 2700 rpms.

 

     Choke Size x 4 = main jet

     main jet + 50 = air corrector

     performance engines can have mains and air correctors closer in size.

     Generally, use smaller auxilliary venturi with larger chokes.

     Main Jet affect mix from about 2500 and up depends on choke size, and air correctors, fuel levels.

     Larger Air corrector leans out the mix towards higher revs and can bring the main circuits in sooner.

     Emulsion tubes are generally "fuel" curve tweakers. Use them later after everything is working, IF you have too.

 

 

 

MECHANICAL FUEL INJECTION

 Accelerator Pump tuning.... I really don't have much advice here except that you can adjust the DURATION of the fuel squirt, and the VOLUME of the fuel squirt independently.  These are the variables: pump stroke, jet size, and bleed size. The little jet at the bottom of the bowls is a check valve that feeds the accell circuit called the Accelerator Pump Discharge Valve.  It also has a bleed back hole.  You can change the size of the bleed back hole, and the pump jets.  Generally leave the pump stroke alone.  SMALLER bleed back hole and LARGER pump jet will make more fuel go to the engine.   Add the two hole sizes together to find your DURATION index. (I invented this. It could be trash theory If the sum of the two is large, duration SHORTENS, if the sum is smaller, duration LENGTHENS. The bleed hole size mainly determines the sensitivity to throttle position changes.  Example: A large bleed back will squirt very little fuel to the accel jet, during slow throttle movements.  When moving the throttle slowly, the fuel will simply bleed back into the bowl instead of going to the engine.  

     

     ANALOGY:  Fill a cup with water, drill two holes in the bottom sides.  One hole feed the engine and the other hole drips back into the sink.  Those are your variable.  Size of the cup, and sizes of the holes.

 

 

 

 

 

 

OK I am sure I missed stuff and there is more to it than that but it's my mental digest.  I didn't talk about synchronizing because that is not really a carburetor tuning thing.  It's more of "put on clean underwear thing."  I am in process of tuning my carbs now.  I am also battling a progression stumble since increasing the choke sizes.  It's all about slow air.  A carburetors WORST enemy.

Edited April 26, 2010 by cygnusx1

[zredbaron]

Every stumble i have ever encountered in triples is because of a lean spot not a rich spot.

 

you can't assume that just because yours was lean that others' are also lean.

 

ok, look. this isn't a pissing match, i've already conceded that a wideband is better than a narrow band. i'm pretty sure i'm allowed to have my dash the way i want it, but thanks for offering.

 

i don't intend to insult you personally, but you do make it hard to refrain.

 

your "experience" simply does not line up with the experience matt and i have had. even if you were 100% correct *for your application* but for ours, that is simply not true.

 

i offer no evidence? once again, *IF* you would have read the thread, you no doubt would remember seeing that we both have offered emperical evidence SHOWING our rich condition, such as this A/F graph:

 

 

 

 

weird. looks like the air / fuel ratio goes low, meaning not enough air, meaning rich. the end.

 

matt's graphs, which you also have seen in this thread, show the same thing.

 

care to take this any further, or are you good? perhaps you can tell us some more about widebands, do they work well?

or, if you like, we can talk about how boosted applications such as yours aren't comparable to normally aspirated setups.

 

If i can tune a blow through weber setup to be perfectly linear than N/A should not be a issue. I dont seem to understand why so many people are having such a issue.

 

oh, look, it seems you've acknowledged the issue, but it "blew" right over your head. weird.

 

tell you what, you find an NA dyno graph with higher output than my 3.1, then i'd be happy to listen to the owner of that car.

 

until then, i'll assume that any higher output is either boosted or fuel injected.

 

in the meantime, i'll listen to the crickets...

[JMortensen]

Hey Mark, on my car with Mikunis I found that running a larger pilot jet was better than running larger pump nozzles. Don't know how that works on Webers, but my thought was always the same as yours, that velocity drops to 0 right at the same time you get a big stream of fuel from the acc pump. My attempts to cure a similar stumble had me going to surprisingly large pilots and I hadn't yet gotten to going to smaller pump nozzles. At some point I would suggest you live with it, because cutting down the venturi sizes is going to limit top end power.

 

Another thought would be to put a cam in the throttle linkage so they open more progressively. Might also help traction coming out of corners. I seem to remember you having issues there, although if I recall correctly they were more related to suspension bottoming out.

[Lazeum]

First I'm glad this thread is becoming alive again. I like the debate about what's wrong but we should keep it as a discussion. I'm learning still!

 

Mark, to answer your question, my distributor does not have a vacum line on it.

 

Just to make sure we're on the same page, my rich spot does not create any stumble (I have a lean spot when I hit the throttle), it is more a lack of torque (barely noticeable) once the car starts pushing.

 

Regarding the horn lenght, I was more thinking about pulse than air flow. since the path for air is different, wave lengh changes moving the system acoustic efficiency somewhere else. I assumed if we have a rich spot it is because we have more air being suck thanks for acoustic pulse. if this can be moved to higher rpm, it would result in more power. That's my guess, there's no facts on my side to prove it. it would require a pressure gauge in my system to check it

 

 

If think something important to do is to set timing at idle the best way possible. I'm at the early stage of tuning now, I've setup the advance at ~15° with good results but I might try to turn slowly the distributor with engine at idle until rpm to get the highest engine speed to see if I can improve the situation.

 

 

Weird thing is:

I was using 50f9 at the beginning. i had to turn the idle mixture screws to 2 1/2 turn to get proper idle.

So I switched them with 55f9, I had to turn not more than 1/2 turn to get someting decent... Car was super rich!

I found out 45f9 worked out quite well with idle screw to 2 turns as well.

It does not make sense to me right now. Something is messed up on my setup I think (leaks???)

 

Shouldn't a port/polish/unshroud head requires more fuel since it might flow better?

I'll think about it this week and get some more actions done next weekend

 

 

My Wideband for info is a LM2 from Innovate. I don't keep it in my car when I'm not tuning

[yetterben]

The funny thing is i can remove my hks box run N/A all day with my afr's pulling hard as a mutha at 10.00 or even 9.00's Dont believe me i just so happen to have the face of the box off and can go make a pull to proove it. You are only really rich between 3,700 and 4 grand. The engine is pulling so much vacuum right there that you would not feel that rich spot. The motor is turning so high that its getting burned off jsut fine. When i had Su's i was pulling down 11's wot on the gauge. I think you are basing carb afr's off efi afr. 12's and high 11's are not rich not at all and in fact should be richer.

 

Remember maximum torque is made while rich max hp is made while slightly lean. I helped someone over the phone a week ago dial in his 40's easy peasy no flat spots no dead spots. The fact of the matter is you should be able to tune a set of triples and pretty much be able to move them to any L6 with very small tweaks needed.

 

The afr gauge isssue is your call your motor. But to say i dont want to get one casue it does not match my other gauges......thats actually kinda ricer would you not say. I know your not but thats the mentality.

[yetterben]

Its gonna be diffrent somewhat for you you have a big ol stroker. I would love to actually drive these cars to see what everyone calls a stumble. Sure if you mean i crack the throttle to much at 1,500 grand it goes flat on its face than yeah thats gonna happen no matter what. Or if you mean it was fine then it went pop and lean backed or bogged for a second and i did not vary my peddle and it picked back up fine, type of deal.

[yetterben]

I sent a pm with my Phone number give me a call mark. I am also a firm non believer of air boxes on triples. Hinders low end performance something fierce.

[zredbaron]

you remember correctly, jon. i've hopefully mended the traction problem - just installed konis and stiffer springs. no road test yet. intend to experiment with removing the rear sway, too, if you remember that.

 

i agree that there's no need to upgrade the pump jet. fuel is not the problem, lack of air is. i assume your pilot jet is similar to our mains, and my current setup agrees with you: the car wants large mains and relatively small air correctors. when it's making power and all is happy, it wants more and more fuel. the head flows well, after all.

 

living with it is what i intend to do. i do want to try smaller venturis to see about improving the driveability factor. it's really the only way i know of to mend my problem, assuming of course that my theory is correct. i'll have to do some research to see if 32mm is too small.

 

The engine is pulling so much vacuum right there that you would not feel that rich spot.

 

how would you not feel it? you're right, it's still making some torque, so it doesn't faceplant like a lean engine does, but it doesn't pull smoothly, either. no popping, this is a well ignited engine with wonderful fuel. there's just no power, therefore no acceleration, and so it just lingers in this poor performance region. i'm not going to keep reposting pictures, but the accompanying torque and power curves show proportional dips as well.

 

i promise that we're not making this up. you reference a stumble at 1500, and we're talking about a car struggling to idle at that speed. it's just not a fair comparison either way. you're welcome to come see for yourself.

 

EDIT -- i think i might experiment with no air box. i remember when i first rebuilt the engine, the sound and responsiveness both changed noticeably (for the worse) when i put the air box back on. i took it for a drive around the block with no box and no hood. just had to do it, of course. point being, i think you might be right about it affecting low end performance.

 

and yeah, no worries, this isn't personal or anything.

Edited April 26, 2010 by zredbaron

[JMortensen]

i agree that there's no need to upgrade the pump jet. fuel is not the problem, lack of air is. i assume your pilot jet is similar to our mains, and my current setup agrees with you: the car wants large mains and relatively small air correctors. when it's making power and all is happy, it wants more and more fuel. the head flows well, after all.

Not too familiar with Webers, but on Mikunis you have mains which is what the car runs on when you are at WOT above say 3000 rpm, and then it has pilots, which are what it runs on when idling, and pumps which kind of bridge the gap. That's oversimplifying a bit and the pilots will actually affect things well into the mains, but whatever the idle circuit is controlled by, I'd go bigger on that. My reasoning was that the fuel was better atomized out of that jet than it is out of the pump, which in the Mikunis really puts a thick stream of gas straight into the engine.

 

I'll be interested to see what happens with your suspension changes.

[yetterben]

Pilots are idle jets in webers and do overlap into mains. Pending where the progression ports are aligned with the throttle blades they affect well up into the high 3'000 range.

 

I was hoping he would call. I am curious as to how he has it idling at 1,500 what means to a end to get it there. Because if he did it with the throttle stops screws and is in front of the 3rd progression hole that explains alot.

Edited April 26, 2010 by yetterben

[zredbaron]

i agree, jon's pilot jets sound like our idle jets. though i disagree for how long the idle jet is active for. i think it's out of the loop closer to 2500 rpm. it's a transitional circuit, after all.

 

as per our discussion, at 1500 rpm i bet my mixture screws are useless, and agree that the progression holes are likely to be uncovered by the throttle plate at idle.

 

not what one would consider ideal.

[cygnusx1]

You know you've spent too much time with DCOE's when, as you drive,  you start picturing the accelerator pumps squirting, and you imagine the fuel emulsifying as is comes up through the main jets!      

 

Great stuff.  The designers of this stuff were pure genius.  Even in today's EFI tuning, a lot of the parameters we control are defined by these carbs.  Keep on tuning!

Edited April 26, 2010 by cygnusx1

[yetterben]

I think rpm is irrelevant as to when the mains come online. I think it has to do more with when there is sufficient vacuum/air flow. Keep in mind idle and main overlap and need to be paired accordingly.

 

Remember if you are past the ports you are drawing fuel from idle and main circuit. The main is not gonna be emulsified and be more like droplets causing rough running.

As per the conversation i think 80 percent of your issues is that box. Airflow is so choked off its not even funny. Seeing as that box has probably no design thought behind it. Who is to say all your flow is not going to 123 or 245 or whatever.

 

Like i said when i was using my hks turbo plenum for a cold air box before the turbo., flow was so hindered it was a struggle to get above 5 grand. It was fine to a point but just fell flat after 3 grand or so.

 

Hell close your idle mixture screws off at see what it does. Bet it dies

Edited April 26, 2010 by yetterben

[didier]

First I'm glad this thread is becoming alive again.

 

 

Shouldn't a port/polish/unshroud head requires more fuel since it might flow better?

I'll think about it this week and get some more actions done next weekend

 

 

well, we are waiting for your results, beware of the iceland's dust ! ah ah !

 

Didier, megasquirter fan !

[zredbaron]

The designers of this stuff were pure genius. Even in today's EFI tuning, a lot of the parameters we control are defined by these carbs.

 

agreed!

[Babalouie]

Speaking of wideband, I just bought one of these guys: http://www.wbo2.com/2j/default.htm

 

AU$256 (which works out to US$235 I spose) plus postage.

 

You can choose to buy the wideband with a display screen for real-time AFR, but if you want to use a laptop, the software that it uses is pretty simple. Just click one button to start recording AFRs before a run. It saves the result in a .txt file, which you can then cut and paste into MS Excel and have a chart against RPM.

 

I haven't installed it yet though, but plan to use to to fine tune my triples

[cygnusx1]

I finally got a chance to test drive the L28 240Z with the new 32mm chokes in the 40DCOE-151's.  Initially when I upped the chokes from 28 to 32 , there was a tremendous hole in the power from roughly 2000 to 3000 with any load on the motor.  I knew I had to tweak the mains and try to get them to come on sooner.  The first thing I did was to get the fuel level in the bowls dead on.  I measured down from the top and tweaked the floats to get 25mm from the carb body top.  That made a big difference.  The levels were low by 6+mm by just going with the float specs for my plastic floats.  Do not trust the float specs.  Measure the level in the bowls!

 

Next I drilled out the main jets from 125 to 135 and then 150.  I also opened the Air Corrector to 195.  The car was better but still bogged on quick throttle in the 2000-3000 range. 

 

Next, I closed off the bleed holes in the accel check valves.  That didn't help and possible made it bog more.  I opened the cover for the Accel pump weights and rememberd that the PO had installed plastic BB's on top of the weights?!?  I have no idea why but I assume he was battling the bogs.  I removed the BB's.  I discovered that one of my Accel Pump check/bleed valves was not checking consistently.  I opened it up and changed the little ball inside the bad valve and re drilled 0.055 bleed holes.  Fixed.

 

Test drive went great.  Plenty of torque, great heel and toe response.  Almost zero back fire on decel from any rpm.  I was still getting a little bog if I slam the throttle open to quickly.  I know this is something that Weber drivers know how to drive around.  Roll the throttle on as the revs climb.  That said, in the interest of driveability, I put the car on a hill and shifted to fourth to get 2000 rpms.  Lugging the motor and making really poor carb conditions with slow air.  I slowly opend the throttle and the motor pulled perfectly smoothly from 2000 and up with the throttle WOT.

 

I repeated the experiment but opened the throttle more quickly, and got a short bog.  I opened it REALLY quickly and got a longer bog.  What does this say?  The accel pumps are causing the bog.   Maybe that's what I WANT to see.  How do you read it?

 

My next step is to put more bleed in the accell circuit.

 

 

 

 

...oh and no lecture about a WBO2.  I know I need one, but Webers CAN be diagnosed without one.   

Edited April 27, 2010 by cygnusx1

[yetterben]

I dont think you can ever completely tune out some bog. You should have no bleed back get a 00 jet so it shoots te whole wad lol. I dunno if there is a way to lengthen the throw on the squirter or not. but if you look at it with the cover off it only works till 3rd throttle. If you could lengthen the throw and increase the level in the holding that would be good. I have done this on nikkis buy bending the throw rod and adding shims to the chamber to increase capacity.