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

[Dtsnlvrs]

i was re-reading this thread and was surprised that i had already mentioned the costs of large venturis. i must be getting old... i've forgotten my own experience. hah.

 

also, i came across this report about the F-16 emulsion tubes.

 

 

 

this furthers my opinion that the F9 is my best-guess. here is a report of the f-16 making an L28 more rich. we want more air, not more fuel!

 

I also did a tune using the 33mm vents and the F-9 e-tubes.....forget the f-9...I would suggest the f-11 or the f-2 (BTW the F-2 is what came in the original Z-car conversion) and increase the needle valve size to at least 1.75.

[Dtsnlvrs]

BTW...having a large set of jets is very expensive, but the cost can be mitigated...for starters...dont buy crap from a US company....most of their rebuild kits are junk and their jets are now cheap chinese copies stuffed into "gen Weber" bags, or overpriced OEM Weber....I only buy my stuff from England or Italy. My jet selection covers 28mm, 30mm, 32mm, and 33mm Main Vents, but I buy my jets direct from italy at half price over the states.

 

http://www.dellorto.co.uk/ rebuild kits..itg filters and misc parts

 

http://stores.ebay.com/ALFA1750S-CARBURETORS-PARTS-STORE Jets and stuff

 

http://stores.ebay.com/FAST-ROAD-CARS another English Supplier

[Zmanco]

When I rebuilt my DCOEs I installed the new needle and seat assemblies just assuming they were the same size as the old. While tuning afterward, I found that I had an intermittent lean condition that could be felt above 4k rpm, similar to what Russell described.

 

I initially suspected I had a fuel delivery problem and swapped the fuel pump and filter with no success. Eventually I put the old needle and seats back in and the problem was solved. I don't remember what size they were, although I'm pretty sure the rebuild kits were NOT genuine weber.

[Dtsnlvrs]

Well I just opened my carbs up, could not find my data sheet, and have compiled all my numbers. I will include specs about the car as well cause that will influence jet selection too.

 

Mind you I am in Las Vegas, 2200-2500 ft elevation. I run the car on pump premium 91.

 

f-54 block flat top all stock (nissan parts).

 

'71 E-88 Head originally built by Sunbelt (large valves) stage 1 port by me on kitchen table with a dremmel tool.

 

2mm HKS head gasket

 

Isky 490 / 290 cam with 109deg lobe seperation

 

'81 NA 5-speed, 4.11 R-180 diff

 

225/50/15 tires

 

Euro (6deg) 240-Z dizzy, Pertronix firing a Jocobs Ign Unit. Magnecor Wires

 

TIMING: 20deg initial 32deg total "all in" by 2500rpm

 

DENSITY ALTITUDE DAY OF RUN. 3600ft

 

40DCOE18

Main Venturi: 33

Aux Venturi: 4.5

E-tube: F-11

Mains: 140

Airs: 150

Idle: 55f9

Accell Jet: 45

Accell Bleed: 40

Needle Valve: 1.75

 

 

 

We got our best (safest) AFR's with the setup above.

 

I am leaning one of two ways...either change to a 2.00 needle valve, and or F-2 E-tubes. My "guy" in Italy suggested years ago that I switch to the F-2 tubes....I will probably do both.

[Dtsnlvrs]

I just found some "new" info with respect to the needle valve selection. According to the Speed Pro Series "How to Build & Power Tune Weber & Dellorto DCOE, DCO/SP & DHLA Carburettors" Chapter 4, Needle Valve Seletcion, p77-78.

 

"One Choke Per Cylinder applications -

Up to 300cc per cylinder use a 1.50.

Up to 400cc per cylinder use a 1.75.

Up to 500cc per cylinder use a 2.00.

Up to 600cc per cylinder use a 2.25.

Up to 700cc per cylinder use a 2.50."

 

So using this chart...a L-24 would require the 1.75, but a L-28 or L-30 and larger should be using the 2.00.

 

This would make sense...if you look at my AFR graph and remember that my Air Corr is only .10 larger than my main jet...I am running out of fuel in the jet well at 4500rpm.....then we get start to get rich again after peak HP at 6000rpm.

 

I think what WE ALL should do is switch to the 2.00 needle valve, ensure we have good fuel pressures, and test. Then make the final judge on our E-tube selection.

[Lazeum]

That's a lot of good info coming up

We start to have more and more AFR reading about Webers.

 

The weber noob I am does not know how to ckeck needle valve. Should remove the float cover? I would have to do some more investigation since I've never tried to take apart the cover yet.

 

Other observation is that you do not have the rich spot as we have with Mark and many others over internet (Actually it is the opposite) Should be interesting to try needle valve as well (maybe ours are too big and fill up too much the well with vacuum at certain RPM)

[Dtsnlvrs]

Follow me here if you will.

 

If you are starving the jets at 4500 rpm, and did not know why...you would put in larger main jets to compensate...We all have fallen into this trap...Large main jets...add 50 for the airs...then run out of gas at 4500rpm.

 

zredbaron has a 3.1L engine...so the disparity between jat size and ammount of fuel available is exacerbated. I think if he would install 2.00 or even 2.25 needle valves he would see the end of his issues. I am going to order 2.00 needle valves tonight, and try that with the F-11 tubes.

[Lazeum]

Follow me here if you will.

 

If you are starving the jets at 4500 rpm, and did not know why...you would put in larger main jets to compensate...We all have fallen into this trap...Large main jets...add 50 for the airs...then run out of gas at 4500rpm.

 

I believe it is the opposite; we have too much gas and not enough air at 4500rpm range but problem might be the same...

 

Between Emulsion tube/float height/needle valve, that's a lot of options to check, to inspect, to see and to solve our problem

Everything look simple on books

[Dtsnlvrs]

I believe it is the opposite; we have too much gas and not enough air at 4500rpm range but problem might be the same...

 

Between Emulsion tube/float height/needle valve, that's a lot of options to check, to inspect, to see and to solve our problem

Everything look simple on books

 

You are reading the AFR's wrong (I think). Look at both mine and Zredbaron's AFR graphs...his start to lean out from full rich at 4k and mine at 4.5k...we ARE running out of gas in the jet well. But the larger jet we use to compensate, causes the dredded bog as the mains come online in my case at about 3300rpm.

[Lazeum]

Whan I look again at your AFR, you're right. You both seem to lean out after ~4k rpm. I would agree with you regarding fuel starvation.

 

On my side, the AFR curve is really flat but I do have a rich spot at 4k rpm.

I would have on my side to go with a bigger main anyway since I'm at 13.5 on the most part of the curve in addition to very low timing to be reworked (10º initial/ 28º total)

 

[Dtsnlvrs]

Whan I look again at your AFR, you're right. You both seem to lean out after ~4k rpm. I would agree with you regarding fuel starvation.

 

On my side, the AFR curve is really flat but I do have a rich spot at 4k rpm.

I would have on my side to go with a bigger main anyway since I'm at 13.5 on the most part of the curve in addition to very low timing to be reworked (10º initial/ 28º total)

 

 

Try adding 5more deg initial advance (15 deg @ idle) the Webers like ALOT of initial advance

[zredbaron]

there are a lot of things i'm inclined to respond to, but i've been waiting for some road tests before piping back in on that stuff.

 

with regard to advance, i agree that webers like a lot; my initial advance is over 20 (not sure how much MORE is added by my MAP sensor, if any?). i'm 'all in' with 29 at 3k (again, plus mystery MAP sensor advance), then i linearly back off to 23 by 8k (again, + mystery MAP sensor advance). i suspect the mystery advance added is about 5 degrees or so. (a very different engine, though...)

 

i do not at all mean to suggest that needle valves aren't important, but the data speaks for itself. look at my graphs. i don't have a problem with being lean. i have a problem with being rich.

 

i agree with lazeum regarding the a/f graphs. perhaps we are all talking about different sections of the graphs, i'm not sure. i'd like to settle it, though.

 

okay. it's called the "air to fuel ratio." meaning, if the ratio is 14.7:1, there are 14.7 parts air to 1 part fuel. right?

 

so any number above max power mixture (arguably ~12.5-13:1, although stoichiometric is 14.7:1 and is a different discussion entirely) is by definition a lean condition, and any number below max power mixture (again, assuming ~12.5-13:1) would be a rich condition. agreed?

 

there is a MAJOR DIP in my AFR graph (and in your graph, datsnlvrs, though yours is a *very minor* dip) from roughly 3500 to 4500 rpm, and again dipping low after about 6000 rpm.

 

again, a low AFR ratio is a rich condition.

 

This would make sense...if you look at my AFR graph and remember that my Air Corr is only .10 larger than my main jet...I am running out of fuel in the jet well at 4500rpm.....then we get start to get rich again after peak HP at 6000rpm.

 

i have to say that i completely disagree with your logic. IF we assume that you're right' date=' that you ARE in fact running out of fuel in the jet well at 4500 rpm, then how is it possible that you are going rich above 6000? if you were running out of fuel at 4500, then you would continue to get leaner and leaner as rpms increase (AFR number gets higher). again, both of our graphs do the opposite: they fall.

 

 

to shift the topic a bit (ie why this happens, so we might troubleshoot in the right direction):

 

here's my line of thinking from my understanding of fluid dynamics (i don't claim to be an engineer, but i do have a fairly decent grasp on aerodynamics). i will compare the progression from 5000 rpm to 7000 rpm for this conceptual discussion (also assuming WOT). as rpms increase, the total volume of air passing through the engine increases. we are talking about carburetors, so we can also submit that *more* fuel from 5000 to 7000 is supposed to be "sucked" in, in order to ideally keep the AFR constant.

 

i put "sucked" in quotations because this is actually incorrect. there is no force in nature that sucks. it is a term of conceptual convenience.

 

the reality is needed for this discussion. the physics of what is going on here is that the pressure INSIDE the venturi goes down RELATIVE to the atmosphere (ie the pressure in your air box). this difference in pressure causes air to flow from high pressure to low pressure; air is PUSHED from the air box into the venturi and ultimately the cylinder. (similar to how water is PUSHED out of a hose; lower pressure is felt on the end of the hose than at the faucet.)

 

there are two things going on here. bernoulli's principle (ie venturi effect) tells us that as the speed of a fluid increases (over the venturi in our case), the dynamic pressure of that fluid decreases. this decrease in pressure is what PUSHES more fuel from our fuel wells, through our jets, and into our venturis (more fuel at 7000 relative to 5000).

 

the other thing thats going on here, is that the air is becoming increasingly turbulent.

 

nomenclature side notes: turbulent air is random in direction and inefficient in terms of flow. think white water rapids. laminar flow is straight and very efficient in terms of flow. think water through a pipe or a hose. comes out clear, not white.

 

[img']http://www.markhaag.com/images/hybridZ/flow.gif[/img]

 

to continue, as rpms increas, velocity increases and therefore the air is becoming increasingly turbulent as it passes through the venturi. (it is likely that low rpms have NO turbulence, as there is a velocity at which flow across a surface changes from laminar to turbulent. [this change is known as stalling in terms of aircraft wings but is caused by other factors.]) as turbulence goes up, the efficiency of flow goes down (and therefore the resistance for flow goes up as turbulence goes up).

 

so, as resistance to flow goes up, more pressure is needed to PUSH the air to maintain a given flow rate. too bad we don't have turbos or superchargers to solve this problem. we still have atmospheric air pushing into our venturis, and it simply can't keep up.

 

however, the relative low pressure is still continues to draw increased amounts of fuel. this is where i believe the air corrector is designed to "correct" for this; displace some of the sent fuel, and send more air in its stead to try and keep the AFR constant.

 

at the dyno the other week, i did change only an air corrector and noted its effect from one run to the next, hoping to flatten the high rpm dip. the frustrating reality was that it did not flatten but merely shifted the graph up or down from about 3500 and above. main jet did the same thing, but also shifted below the pivotal air corrector rpm.

 

this damn carburetor seems like it would take a graduate project at an engineering laboratory to explore fully. sigh.

 

so. the point of all this is simple. in my mind, we have two separate rich-seeking trends on the graph, one at mid-range rpm and one at high rpm. i believe the high rpm problem to be independent of the mid-rpm problem.

 

i suspect the high rpm problem is a limit to carburetors in general, and you can only minimize its effect via the air corrector. i don't think we will ever make it go away. [that's not completely true, a larger venturi would help this problem greatly, but would worsen driveability.]

 

i suspect the low rpm problem is a CAUSED by large venturis, and EXACERBATED by floats/needle valves/jets/timing/etc.

 

but hey, what do i know? i didn't design it. this is just what i believe based on thinking about it.

 

there's probably some weber expert out there in a shack in new mexico that can tune my webers perfectly. it seems the weber engineers were some pretty smart bastards and thought of things most of us don't even know about.

 

that doesn't change the fact that we're all still just getting them 'as close as we can' to tuned. there's a reason carbs don't come on new cars anymore; mechanical things simply have their limitations.

 

-mark

[zredbaron]

also, thanks russell for your links! i was able to order some new idle jet holders that i've been looking for for a very long time. i think i might buy that 'official' weber manual, too...

 

[Dtsnlvrs]

also, thanks russell for your links! i was able to order some new idle jet holders that i've been looking for for a very long time. i think i might buy that 'official' weber manual, too...

 

 

Glad to help with the links.

 

I think we are talking about the same thing but using a different perspective. On our motors with similar cam profiles, Our mains should be comming in at about 3k rpm...just when we start to richen. then around 4k we both go lean, compared to how rich we were. If the jet well is drying up, that would would explain the lean condition...if you cant keep the well at the "right" level, all bets are off. I look at it this way....3 needle valves is a cheap experiment compared to 6 E-tubes. Besides....The English book says we should have the 2.00 valve, and every OEM application for a 450-500cc per cyl calls for a 2.00. I figure its worth a try. If I replace the valve and the leaning goes away...I can reduce my main jet and get the AFR graph more linear. As far as going rich at the end.....we are both past our usable HP and therfore the motor is not as effecient...so who cares. Just my .02

[zredbaron]

very good. hey, i could be out to lunch, who knows. it *IS* worth a try... let us know how it works out!

 

also of note on that euro site:

 

damn good stuff...

[zredbaron]

speaking of links, i just found this fantastic article. lots of great info and pics all in one place...

 

http://www.tjwakeman.net/TR/WeberDCOEinfo.htm

 

particularly of note, it shows differences in float settings based on model stamps, discusses some idle adjustments that the books don't (a venturi bypass air screw!?). definitely a must read...

[Daeron]

Mark: I think that what the Sergeant is trying to say is that the fuel flow into the jet well is not properly inhibited (by which I mean to say, OVERLY inhibited in this case) and that improper fuel flow characteristic, and corresponding variations in the jet well, causes you to "correct" other jetting settings in a manner that brings out your two rich "dead" spots. He seems to be saying here:

Follow me here if you will.

 

If you are starving the jets at 4500 rpm, and did not know why...you would put in larger main jets to compensate...We all have fallen into this trap...Large main jets...add 50 for the airs...then run out of gas at 4500rpm.

that everyone is using jetting to band-aid over what is essentially a fuel starvation issue, but a post-float bowl starvation issue.

 

 

I am really fuzzy on the carbs, so I may be mis interpreting, but if you look at the AFR graphs, you REALLY have to look hard for the rich spot in his setup, and his lean(er, there arent really any LEAN spots) spots seem to be his primary deviation from standard.. *maybe* he is slightly richer than ideal across the whole board.

 

Again, I may be wrong, because I am in WAY over my head as far as the carbs go.. but I think I am understanding what he is trying to say better than you are. 'Course, I could be tooting in the wind, too

[Dtsnlvrs]

^^^^ very well put ^^^^

[Dtsnlvrs]

speaking of links, i just found this fantastic article. lots of great info and pics all in one place...

 

http://www.tjwakeman.net/TR/WeberDCOEinfo.htm

 

particularly of note, it shows differences in float settings based on model stamps, discusses some idle adjustments that the books don't (a venturi bypass air screw!?). definitely a must read...

 

My carbs do not have that screw 40DCOE18, yours do 40DCOE151

[Lazeum]

Regarding needle valve, I've read this is (not only )

The needle valve needs to be large enough to allow an adequate flow of fuel into the float chamber but should not be larger than necessary. Too large a valve will let too much fuel in quickly before it closes and cause a pulsing over rich condition.

 

In another word, it makes me think our rich/lean conditions could come from the needle valve too big in my case, it does not close enough quickly enough the flow in the bowl and create the rich spot I experience.

I guess it is going to be an easy check worth a removal of the top cover of the carb

 

This is going the same way the guys on innovate forum talked about to solve the rich/lean mid rpm condition. By playing with the height of the fuel might solve the problem. Actually I believe it will move the problem somewhere else instead of fixing it.