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

[zredbaron]

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.

 

after writing this, i was thinking that i thought it was between the f16 and the f2, not the f11. here's the table that i was recalling:

 

Cylinder capacity.......................Suggested tube

250-325 .................................F11

275-400 (L24) ........................F15

350-475 (L24, L26, L28) ..........F9, F16

450-575 (L28, 3.1 stroker) .......F2

 

[source is NOT the weber book, but this common guide: http://members.aol.com/dvandrews/webers.htm]

 

so instantly, i'm thinking oh, man am i running the f11 still? sure am!

with a 3.1, i couldn't be any farther off! i've never touched the emulsion tubes because most sources say that its rare that you need to change it.

 

again, i don't know for sure yet, but i find this promising. i'll be ordering some f2s soon and i'll report my findings. (anyone try the f2?)

 

"The emulsion tube controls when the air correction jet becomes significant and the rate at which its significance increases." (weber book)

unfortunately, the weber definition above sounds to me like a higher rpm influence rather than a lower rpm influence that might be responsible for our studder.

 

in short, i'm still guessing like everyone else...

[Zmanco]

Zredbaron, I've since gone on to megasquirt, but when I switched to a distributor that was controlled by the MS (in other words, I could choose my own advance curve via the laptop) I found that by running a lot more advance at idle and low revs (<2500 rpm) I had significantly improved drivability. For example, I'm running 20 degrees of advance at idle and have full advance of 35 by 3000 rpm. This is with what most call a stage III cam.

 

My point in telling you this is that I think your theory that the stutter is tied to spark advance is indeed correct.

[akumazeto]

So the possibilities could also be my timing. I do run a 280 distributor.

As for the turns on my screws. I turn them all the way closed to seat then turn them 1 full turn then a half turn.

 

Im really new to the carb scene but Ill do what I can.

Thanks everyone for their support and help and if anyone else has suggestions please feel free to let me know.

[Lazeum]

I've got some news regarding the car.

I've done some logs with a wideband this past weekend and I've got first answers to my questions

 

- My AFR are rich everywhere, I'm always between 10.5 and 12.5 with very rick peak when I hit the gas pedal.

- Idle is at 12.0/12.5

- Ticking noise: knowing that my engine is running very rich, it would make detonation out of the picture

- Spark plugs were black last time I've checked but they were brown before. I might have removed some leaks between carbs and manifold; ticking noise decreased a lot since I've played with mounting bolts. AF mix might have been leaner before.

 

So next step for me:

- Idle adjustment

- Cam lash adjustment

- Carb tuning. should I start with main jets to lean everything or with idle jet?

 

I post a screen shot of a log. I'm learning how to use WB so no WOT logs yet...

[Lazeum]

I fixed my detonation issue I've lowered the advance timing. I'm now running 10 initial and 28 total.

I will adjust the timing, try to shoot for something close to 20 at idle as suggested

 

For my timing story => http://forums.hybridz.org/showthread.php?t=140950

 

Now that I'm not running a sick engine anymore, I've done some WOT pull AFR logs.

 

This is what I came up with

 

I need to adjust timing first I guess.

 

The car nose dives at the beginning of the pull.

We can see when I hit the gas pedal that I start to run rich then very lean before the run rich again afterwards. It seems the accelerator system is not working the way it should (duration + mixture seem out)

 

I've got a rich condition at 4700 to 5200 rpm I do not explain. I would guess it is the emulsion tube.

 

The rest of the curve (flat spots) are a little lean but I guess there are quite ok for now.

 

I'm waiting for your feedback and your thoughts

 

 

FYI my setup as a reminder:

F54 L28, N42 head

flat top pistons, 274 Schneider Cam

3x 40DCOE, 2.5" 6-2-1 header/exhaust

Mallory ignition (Unilite + Hyfire 6AL)

 

The jettings:

Main 130

Air correction 180

Idle Jet 50f9

Emulsion F11

Accelerator pump 50

Venturi (choke) 32mm

Aux venturi ??? probably 3.5"

[zredbaron]

thank you zmanco. i think so too. testing soon!

 

finally got the f2s. although not a night and day difference, there's no question that the car liked the change from f11. the power band seems smoother, almost like a more complete burn. not much a difference (if any) in power, just smoothness and overall driveability throughout the main circuit's rpm range. i did notice a small drop in the flat spot, but it could also be from lower ambient temps giving me more power. damn multi-variables...

 

i bought them from top end, and according to them, any L6 should have them and their selection has nothing to do with displacement per cyl.

 

this contradicts the aforementioned article, but hey. food for thought. my car liked it. perhaps others can report.

 

i'll report on my timing findings when i have them. should receive a MAP (manifold absolute pressure) sensor soon, which will allow my ignition to vary its timing based on load (ie throttle position). hopefully it will help eliminate the dead spot down low.

 

-mark

 

lazeum, your timing seems a little low. i'm by no means an expert, but i believe our cars in general like full advance to be closer to the mid 30s range. my advance is more, but then again, my engine is more radical. i would suggest some dyno time to determine without any doubt what your car wants to see! as for your nose dive it seems all of us have experienced this with the L6 / weber combo. as suggested above it is suspected to be timing based on engine demand. definitely try the f2 emusion tube and see if that clears up your mystery rich condition at 5k.

 

We can see when I hit the gas pedal that I start to run rich then very lean before the run rich again afterwards. It seems the accelerator system is not working the way it should (duration + mixture seem out)

 

don't confuse the two. the weirdness you mention is our flat spot, not the [accelerator] pump jet / system. (you are 'hitting the gas' at low rpm then doing a dyno run.) this system is a single spurt of extra gas mechanically pushed by your foot when you get on the pedal. it might be a half-second worth of fuel, therefore is not an rpm range. think throttle response, not acceleration.

 

running rich does help combat detonation if you are approaching it, but it does not prevent it. timing and octane do. if you still have a ticking, especially if partial or full load sounds like there are marbles rattling around, then you need to back off your timing or get some better fuel! whenever i heard the warning signs it was under load, not at idle.

 

as for what to work on first idle or main, they are independent of one another and therefore order is of no consequence. the main jet is more important to have right than either the idle or air corrector, but all three are very relevant. get some plus/minus sizes for all three and start experimenting on a dyno or an open road. dyno is best.

 

me, i dyno after significant changes to make sure my timing is right. i of course get mixture too, but seasons change and necessitate changes in jetting. my timing stays untouched after the dyno unless mods require a new baseline (fuel change, compression change, head/cam change, etc).

 

good luck!

[bjhines]

 

Yes... It falls flat on it's face at WOT under 3k RPM due to the large chokes and late comming on the main circuit.

...

[josh817]

bjhines did you make that air box?! I like it very much!

 

Same thing happens to my baby except mine seems WAY more dramatic. For instance, today at school, the stop sign is on a hill and some junior chick pulls up RIGHT behind me. My clutch doesn't like to slip so I have to drop it and floor the sucker. When I floor it, nothing happens and you think "oh god I'm going to stall out in the middle of traffic" but then all of a sudden it kicks in. This gap in time from when its dead and then all of a sudden alive is like a good half second, its pretty bad and its not a fun ride when its a 3.1L with all that torque... really plants you in your seat. Now if I gradually get on the throttle, bring the rpms up above 2500-3000 then floor it, I'm fine.

 

I haven't bothered to sit down and check out what I have in the carbs. Using a link Zredbaron posted I think it was, I came up with:

45mm carb

40mm venturi

160 main jet

210 air corrector

F2 emulsion tube

 

Now unless I find some cheap 45's which I missed out on some on ebay! Really nice! :[ But 40's will work with a large venturi I bet. Since I'm still learning and I'm not sure how horsepower feels in the butt, I know what torque is like, but one of them drops off dramatically at 5500RPM so I'll say torque. My point is that when I go on my rampages I never really hit 6500, I've done that one time because at 6000 I get bad thoughts of what if my motor blows up, I'll have to cry. Since I'm not using an excesive top end, I think smaller venturis would be lovely for the streetability to get rid of that nasty spot. The only way to get around it really is if you are doing like a drag run and you bring it up to 3000rpm and drop the clutch. Don't like doing that either though. As far as timing goes, our timing light is showing what you guys call for (20º idle 35º by 3000), however my idle will not drop below 1300rpm ever and I personally don't like it that high. Is there any other way to check for detonation? My Z is rather loud so any "marble noises" I don't think I'll hear, especially in a garage on a dyno.

 

That blip in the throttle when you floor it only occurs when you floor it and the explanation of you pumping a tone of gas in when you open up the throttle that quickly makes perfect sense. Same reason why I pump the pedal a couple of times before I start the motor. You can't really tell in this video because I'm not opening them up 100% but you can hear a slight blip at first. Once its spinning up, its just fine.

 

http://www.youtube.com/watch?v=wpCa0hC47QU

^Video from under the hood

 

http://www.youtube.com/watch?v=asM-MVAg9LA

^Irresponsible, innapropriate street driving. :] Hey it shows how the motor responds when getting on it hard at a moderate rpm rather than from idle!

 

*mumbles*also shows how hard it pulls (atleast in my mind)from 20-90mph >_> *cough*

[bjhines]

The overall body size of the carbys is WAYYYYYYY bigger than the useful venturi size.

 

Most 40mm carbys came with 28mm chokes.

My DCOE 45mm carbys are using 32mm chokes. That is for track use ONLY. They are shitty on the street.

 

I tried 28mm and I tried 34mm chokes. The smaller the chokes the more responsive the carbys are at midrange RPMs. The larger chokes do not provide enough vacuum to pull fuel through the main circuit until you are over 4k RPM @WOT.

 

ANY street driven Z car should be using the smallest chokes possible. 28mm is a good starting point. The larger the chokes the harder it will be to tune and drive.

 

 

Ohh.. and as a side note...

Changing the choke size will change everything!!!! you will need to COMPLETELY rejet every aspect of the carbys with any change in choke size.

[ZR8ED]

In my not too humble opinion, I don't agree with the small chokes in a Z. I ran 34's and then 36's (40 dcoe) and I briefly ran 38's with 45mm dcoe's. I did not like the 38's, as it flattened out the low end too much. The 34's ran out of steam above 7k, and the 36's were perfect. I ran 5.7 sec 0-60's with the 36's. I also don’t agree with larger than 40mm dcoe’s on a street car. Running 34mm chokes with 45mm carbs are just a waste of money.

 

This is in a beefy 280.

Motor was a L28 bored 40 over, flat tops, 240 rods, polished everything, N42 head from hell with a Shnieder 495 lift 290 dur cam, Nismo exhaust, 10.5:1 compression, blah blah blah. A pretty cool motor good for 8k. Search some of my old posts about that engine. After 5 years, I sold that motor to a guy in LA who dropped it as is into a stock 240, and ran a 13.0 second ¼ mile first time out.

 

A street Z should run between a 30 and 36mm choke depending on if it is a stocko used l24 to a wild overbored L29 or L31 (diesel crank) 40DCOE are plenty of carb on a street driven Z. Even 45's choked down do not have enough flow for street rpm's, and are a compromise for street Z's.

 

A note about Emulsion tubes, F16 is in my personal experience one of the best jets for our cars. Remember that emulsion tubes adjust the RPM in which idle jets transition to mains.

 

A lot of you guys seem to be running very large mains, which can kill your bottom end, where your air correctors and accel pump jets have a larger affect for top end WOT mixtures. Accel pump jets have the biggest effect on sudden WOT response, and to a lesser degree WOT.

 

Sorry for the kinda choppy post, but I gotta get back to work.

I’ll post again some links to some of my Z specific jetting/tuning how to’s.

 

Scott.

[zredbaron]

ANY street driven Z car should be using the smallest chokes possible. 28mm is a good starting point. The larger the chokes the harder it will be to tune and drive.

 

you sir, are 100% correct. i've forgotten about this detail along the way somehow. driveability! he's right... bigger chokes means higher peak hp, but less driveability. i'm running 36mm chokes for the record. weber book wants me at 38-40 for my setup (again, peak hp). think road racing, not autocross or street!

 

 

 

i went to the dyno today and i have the graph to back up the effect of big chokes. i brought the most complete jet kit i've ever heard of, and my a/f ratio graph was unfixable.

 

i even had the MAP sensor for advance based on load (or lack thereof) we talked about. helps smooth out the mid-throttle transitions and makes it more driveable, but does NOT help or fix our flat spot.

 

after tuning the car for timing/mixture for peak hp, i then swapped from the [new] F2 emulsion tube back to my [old] F11 tube. all graphs below show the difference, so you can see the effect of this particular swap for yourself.

 

the red plot is the F2 tube, the blue plot is the F11 tube. unfortunately for most, this data is somewhat skewed in that it is tested on 109 octane vp race gas. it's oxygenated, so i run larger jets than i would for normal fuel.

 

that said, here's what the change did:

 

A/F RATIO:

 

as you can see, the ENTIRE curve is richened by this tube. i ran out of dyno time, but when i get a chance for a road test, i will compare the F2 setup to a setup of F11 fitted with (main -5) and (air corrector +10 or +20). i might not be doing this till next summer, but if i remember, i'll post my preference here.

 

 

 

TORQUE:

 

preference on these two plots is debatable. for torque plot, I like the F2.

 

 

 

POWER:

 

also debatable. i still like the F2 on paper.

 

 

 

again, road test of the comparison with proper main/airs is still needed.

 

and if you're interested, here's a video of the dyno run:

 

 

good luck out there!

-mark

[zredbaron]

scott -

 

you say you prefer the F16? what others did you try?

 

thanks!

[Lazeum]

That is great info, Mark!

The bad point is the F2 emulsion tube did not help to lean the rich spot as hoped.

 

I'm still confused about it, why do we see it? Could it be related to choke (venturis) diameter? Emulsion tubes? Auxiliary venturis? Others?

 

I'm in the order of looking for some extra jets and emulsion tubes. I was going to give a try with F16...

Weather is now cold and rainy but as soon as it is going to be better, I'll try to make some progress on my side as well.

I'm learning a lot so far, it's great My car is runnung better and better!

 

Regarding choke size to be as small as possible, I kind of disagree. Around my town, there are only twisty roads, the fun is in the high revs also. Reasonable choke size is nice to have to push the engine a little. I would believe max torque would be best at 4000rpm for road car.

 

btw, nice numbers on the dyno

[zredbaron]

sigh....

 

http://www.alfabb.com/bb/forums/carburetors-fuel-injection/102770-f16-vs-f9-emulsion-tubes.html

Theoretically I could have gotten the same leaning effect with F16s (fewer air holes)' date=' but the F16s were too rich down low--I was getting a stumble @ 3500 rpm, at the transition to the main circuit. The pairs of air holes higher up the F9 cured the stumble. Again, I could have cured the stumble by using smaller mains, but that would cut power all through the rev range.

 

If the F16s are working for you, don't go through the brain damage of changing everything. If you need more fuel flow, and increasing the main jets (the first thing to try) doesn't do enough, or you need to go leaner high, and increasing the air correctors (the first thing to try) doesn't do enough, or you need to go leaner low, then it makes sense to experiment with different tubes, along the lines I sketched out.

 

F11 first: The F11 is the same basic configuration as the F9 except that it has an additional 4 x 100 air holes (F in the diagram) low down, which is for leaning @ high rpm. The F11 is also narrower, with an OD of 8.0, which means that there's more fuel in the emulsion tube well. This means, in general, that the F11 will flow more fuel.

 

[/quote']

 

that said, we have the graphs for f2/f11 comparison above.

 

The weber book lists f9, f11, and f16 as 'common usage' and lists f2 as 'leaner low end and throttle response.'

 

whatever 'and throttle response' means.

 

again, i saw f2 as being richer across the board today.

 

side note: the weber book is on google!?

http://books.google.com/books?id=TXE-L2QhoAwC&pg=PA163

 

 

lazeum, if i had to guess, and it *IS* a guess, i'd guess the f9, since the f9 seems to have come on later model year production cars that had larger displacement more consistent with our Zs, and the alfa guys found that it was leaner down low, which is what we need.

 

at this point i think its *caused* by large venturis, but might be *patchable* by emulsion tubes that help compensate. i dont think it will ever go away completely unless we go back to the lands of small venturis (28-30mm).

 

thanks! i was very pleased with the dyno run. not willing to sacrifice 25-50 hp (who knows how much, really) for a correction i can do with my foot if need be.

 

let us know which tube you go with... if you can do dyno comparisons, that would be HUGELY beneficial...

[Lazeum]

I'm planning, before to change everything, to record dyno curves and AFR curves

So far, dyno measurements haven't been very successful but I'm making progress (I'm going to use an inductive pickup on spark wire or most probably on coil wire to get higher amps reading)

 

I've also spotted some leaks between carbs and intake. I don't know yet if it is coming from the choke not being off completely or leak at seals (maybe due to my mistake of overtorquing the carbs on the manifold in the past)

 

For sure, I'll post my results (good or bad )

 

Matt

[bjhines]

In my not too humble opinion, I don't agree with the small chokes in a Z. I ran 34's and then 36's (40 dcoe) and I briefly ran 38's with 45mm dcoe's. I did not like the 38's, as it flattened out the low end too much. The 34's ran out of steam above 7k, and the 36's were perfect. I ran 5.7 sec 0-60's with the 36's. I also don’t agree with larger than 40mm dcoe’s on a street car. Running 34mm chokes with 45mm carbs are just a waste of money.

 

This is in a beefy 280.

Motor was a L28 bored 40 over, flat tops, 240 rods, polished everything, N42 head from hell with a Shnieder 495 lift 290 dur cam, Nismo exhaust, 10.5:1 compression, blah blah blah. A pretty cool motor good for 8k. Search some of my old posts about that engine. After 5 years, I sold that motor to a guy in LA who dropped it as is into a stock 240, and ran a 13.0 second ¼ mile first time out.

 

A street Z should run between a 30 and 36mm choke depending on if it is a stocko used l24 to a wild overbored L29 or L31 (diesel crank) 40DCOE are plenty of carb on a street driven Z. Even 45's choked down do not have enough flow for street rpm's, and are a compromise for street Z's.

 

Scott.

 

 

Scott, You post in disagreement about choke sizes and in the same post you inform us of your 13 second, modded L28. My experience is not from just one car. Your engine may make fine use of larger chokes, but the Datsun/L6 kits these carbys came with are not that large.

 

Secondly you are hunting for power above 6Krpm. A street driven Z car needs torque at lower RPMs to be "fun to drive". Larger choke sizes and street drivablilty are mutually exclusive. If you want both then go EFI.

 

I noticed a few comments about the large choke size results from a chart. There has been a commonly available chart for some time that has been mis-read by a large number of people. If it is the chart I am thinking about, RE-check your math, The chart is for a FOUR cylinder engine using 2 carbys. We have a 6 cylinder engine that uses 3 carbys. You need to plug in displacement values that are only 2/3rds actual displacement for the numbers to work out correctly.

 

There are a lot of ways to get good driveability out of a set of DCOEs. I am not saying that you cannot get good driveability with the larger chokes. It will take a great deal of time and money to finally get that tune. The larger choke sizes make the carbys much more sensitive to ambient conditions and fuel quality even if you find just the right jets for any one set of conditions. This means you will need a notebook and a year to tune for all conditions.

 

You may have had good luck with the larger chokes, but I know for a fact that a shop could never turn that tune over to a customer and expect it to work for more than a few months or in rainy weather. Most S-30s do just fine with 28mm chokes. The DCOE 45s are considered a race only carby and most class-limited L6s run 30-34mm chokes.

 

The Weber DCOE design is a highly tuneable carby. It gives the user control over virtually every aspect of metering. It does have it's shortcommings. The lack of a power-valve/circuit can make these designs a little harder to street than the typical Holley. It is ironic that a Holley built for road racing will typically have the power circuit disabled and the main and transition circuits jetted much more like a Weber.

[zredbaron]

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.

 

Well my F-16 Emulsion tubes came in today and I re-jetted to suit.

 

33mm chokes

4.5 aux vent

F-16 emulsion

135main

180 airs

50f9 idle

45 accel

50 pump bleed

 

Conclusion...I was better off with the f-11. The f-16 is too fat, however the change in Idle jets was in the right direction....smells better and is a little more crisp at the crack of the throttle, but once the mains start coming in it flat out bogs...ever seen your A/F meter register full lean cause you are so rich!!

 

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!

[ZR8ED]

BJHines.

 

I mostly agree with your statements. Where I live, most of us Weber users, actually most z owners only drive our cars for approx 4 months, and thus we can get away with a near optimum tune, and just leave it. I personally used 2 sets, as I lived in an area of high elevation and raced at a lower elevation, so I had two sets of jets, that I could run that would take into account high temps and/or high altitudes. Yes I did take a tremendous amount of time, and I had a jet collection that could rival just about anyones personal collection. I have taken detailed notes and compared very slight changes and tested their effects both on the track and the street. (I have tuned street Z's that are mainly weekend warriors)

I was forced into many of the tuning stages on my own car, as it progressed from a near stock L28 through various stages of mods over 2 completely different drivelines, from 4spds to 5spds, and various R200 configurations wheel sizes and suspension configurations which all had effects on jetting.

With no changes to the rest of the car, only nessessary jetting changes, I swapped on a set of 45mmDCOE's with 38mm chokes, and lost almost 1/2 second in my zero to 60 times from my 40DCOE's with 36mm chokes. I was not able to to tune it any better than that, and I was not able to noticeably benefit from the 38's in the top end, so I swapped the 40's back on, and I learned the lesson of bigger is not ALWAYS better, but pretty big worked well.

 

 

I have jetted dozens of Z's, up in my neck of the woods, as well as a dozen or so more via the net/email. I also used to buy/rebuild and sell them as a hobby. (I am not a mechanic, and I only tinker with Z's) This flat spot that most people talk about does not have to be present, It can be tuned out. My main purpose when helping people tune their webers was mostly centered around getting rid of major stumbles, misses, and flatspots in the power band.

I don't think it is worth all of the hassle and expense if you are going to run webers on a stock engine, or for someone looking for absolute driveability at the sacrifice of hp. Just as many have already stated, Mikunis are better suited for a street driven Z, as they do not have the same degree of compromises for tuning hp vs driveability. Even the Weber books make it clear that they are a "No-Holds-Barred" type performance carb.

 

That is why I generally stay away from the smaller chokes on all but the most stock of engines. The weber books are mainly guides, and if you follow the stock jetting list for a stock l24, I have found that to be a less than ideal tune, and is best suited as a starting point to at least get it running.

 

ZREDBARON: I have done a little testing with F2's, but mostly with F11's and F16's. It has just worked out over the many engines I have tuned, or witnessed the final results of tuning, the F16 has ended up by far the most succesfull in a broader range of engines. Experimenting with emulsion tubes is generally not recommended, as you can't just put in a new set of emulsion tubes and think that it will fix your problem. Changing "E" tubes usually requires rejetting the mains/airs/and accel pump jets. It is and always will be my opinion to begin with F16 E tubes, and tune from there, but then E tubes are not cheap, and sometimes you need to just work with what you have.

 

 

It really is nice to see this thread kept alive, it really quieted down for while.

Scott.

[zredbaron]

thanks for the report, scott.

 

with regards to the f16,

It has just worked out over the many engines I have tuned' date=' or witnessed the final results of tuning, the F16 has ended up by far the most succesfull in a broader range of engines.

[/quote']

 

what exactly does 'it just worked out' or 'most successful' mean? are these street engines?

 

i agree the main/airs need to be changed, too.... but in what direction? what i really want to know is what happens to the mixture at mid-range rpm? did it go rich or lean? (ie did your mains and airs need to get bigger or smaller?)

 

thanks!

 

-mark

[ZR8ED]

ZREDBARON:

 

I have tuned mostly street Z's and a handful of dedicated race Z's I learned what I know from two tuners with 20+ Z experience. One with street only, and the other with mainly race only applications. I did most of my work in the early to mid 90's, and I basically have been out of the weber scene since about 2003, so it's been awhile. I don't have my notes handy right now, but with this thread seeing action, I'll have to dig them up and share some of what I have.

 

 

As far as "just worked out", I mean it was the most successful at tuning out the dreaded mid range dead spots. The f16's bring on the effects of the air corrector earlier on in the RPM range. In general terms, you would end up with a slightly smaller main jet, a slightly larger air corrector, and would allow a larger pump jet.

 

Look. In the end, there is more than one way to skin a cat so to speak. All of the jets work in unisyn with eachother, and it is just a matter finding the combo that works for you. What i'm trying to say is that you can get a similar tune on the same engine with totally different combo's of jetting. A smaller air corrector will richen the top end, but can cause you to require a smaller accel pump jet. If you need a larger pump jet to help with sudden WOT response, then you will end up needing a larger air corrector to lean out the top end a bit. Its a kind of give an take, as some of the jets overlap eachothers rpm ranges.

 

I have also seen very little mention of people checking their float settings. This too can have a dramatic effect on main jet selection. Improper float settings usually result in unpredictable fueling of the engine, especially when the fuel pump cuts in and out to fill the bowls. I have found that mechanical adjustment of the carbs to be as important if not more important than jetting when initially tuning the carbs to your engine demands.

 

I have been searching through some of my old post on zcar.com where many different discussion went on in the mid 90's and there were a pile of "weber warriors" I have found lots of jetting combos for various states of tuned cars. I'm compiling some of it (my old notes were pre/early internet) and all hand written. I'm also looking at some of my tuning howto's, and am bringing it all back into my computer so i can have an electronic record. I have not yet searched the hybridz site, as it was created much later on, and I was getting out of webers a while after I joined up here.

 

Sorry I don't have all of my answers off the top of my head, but I'll get back into it and post some of my results. It will take some time.

 

Geez. I may have to buy another z and tune up a set of webers again..I miss that sound..

 

 

Scott.