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

[cygnusx1]

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.

 

 

 

 

I tried a ZERO bleed back and it seemed worse.  It seems the slower I move the throttle plate the better the motor likes everything.  I think the accell pump is OVER doing it.  I will confirm/bust this by adding more bleed.  I am running a 13lb flywheel so the motor responds really quickly.  Maybe that's why the pump needs to be leaner...? Testing resumes.  

Edited April 27, 2010 by cygnusx1

[yetterben]

It likes it cause your not introducing 10 lbs of air in a 5lb bag situation. once you get passed 1/3rd throttle the plunger is down all the way. Where are you initiating these sudden accels.

Edited April 27, 2010 by yetterben

[cygnusx1]

It likes it cause your not introducing 10 lbs of air in a 5lb bag situation. once you get passed 1/3rd throttle the plunger is down all the way. Where are you initiating these sudden accels.

 

From about 10% throttle or less.

[cygnusx1]

 my pc keeps double posting,,....argh 

Edited April 27, 2010 by cygnusx1

[yetterben]

Educated guess no air velocity at such a low rpm. Opening a big gaping hole right to the intake valves.

[cygnusx1]

Educated guess no air velocity at such a low rpm. Opening a big gaping hole right to the intake valves.

 

 

 

 

Oh yeah you are dead on with that guess!  But like I said, I can roll the throttle on from 10% to WOT in about 3 seconds and the motor takes it like a champ.  If I do it in 1 second, she bucks a little.  If I snap it open she bucks for about 2 seconds!

Edited April 27, 2010 by cygnusx1

[cygnusx1]

 double post again!....wtf

Edited April 27, 2010 by cygnusx1

[yetterben]

For general info.

 

BRASS FLOATS COLLAPSE AT 12psi of boost

PLASTIC FLOATS CAN SNAP AT 18psi.

 

 

END TRANSMISSION.

[yetterben]

Specs for plastic floats.

[FubarI33t]

I just received my first set of Weber 40DCOE18 with No 3L. No idea who made the intake. It's really short and says London on it. So far out of the crusty carbs, i have been able to get these numbers.

 

30 Chokes

50F9 Idle

100F5 Starter

40 Acc Pump

Brass Floats

 

I have not been able to get the other's unscrewed. got them soaking. These will be rebuilt for a F54/P79 with no mods. Plan to use these on a DD car.

[Babalouie]

Thought I'dd add my recent experiences to this thread

 

Here's my motor:

L28 bored to 2950cc

11:1 flat tops

N42 head with lots of big/nasty headwork

252 (@50 thou) degree cam/505 thou lift

40DCOEs

 

For a long time, I ran 32mm chokes, and life was good I could pretty much just floor it at 2000rpm and the car would just...go. Then one day I got greedy, and fitted 36mm chokes. Went to the dyno with this setup:

 

Choke 36

Mains 140

Airs 200

Idles 60F8

Tubes F11

Pump 45

Aux vent 3.5

 

Result was an aborted dyno run when it got really lean in the midrange.

 

At that point I figured it would make sense to install a wideband o2 sensor:

 

It wasn't difficult to install (although I couldn't get the rpm readout working) and hooked up to my laptop, where I could record runs and chart the results in Excel later.

 

Take 2

The chart starts at 2500rpm and goes to 6500rpm. It was a little too rich in the midrange and the response was a bit lazy. But more of a concern for me was that the cruise AFRs were really rich and hovered at the high 10s and low 11s most of the time on light loand and part throttle. It also smelled rich and blackened the plugs a bit. But overall, very smooth response with only a small hiccup at 2800rpm. But I felt like I was backed into a bit of a corner here, I experimented with going down a size in the idles, but it start getting a bad hesitation at 2700rpm, and since it was already too rich in the midrange, I felt that going up a size in mains to compensate wasn't the answer.

 

Take 3

I tried a richer F16 tube next, in conjunction with leaner mains and idles, but I think I went too far on the idles. It ran very poorly below 3000rpm, and even with a small throttle opening, would start to hiccup with a light load. This is not a power run, but just the AFRs on cruise, with part throttle from 2500-3500rpm, which suggested things were too lean.

 

Take 4

Bumped up the idle jet size to 55F9 and driveability got a lot better but not great. This is the AFR curve on a full-power run, and you can see the big lean spike at 2500rpm (where it did a big fat hiccup!). But then after that the AFRs are pretty flat. Cruise AFRs are more or less in the ballpark, 13-14 on part throttle and light load.

 

Take 5

Decided to ignore the low rpm for now and fix the midrange and top end. Went leaner on mains to 140, but the airs look to be too lean.

 

Take 6

Didn't get a chance to record the run (it's hard to do by yourself!) but everything was the same as Take 5, but with airs reduced to 185. Now it's at the high 12s just before redline, so I think that's probably sorted.

 

...and that's where I am at the moment. It's very nice and crisp above 3500rpm, and below 3000rpm, pulls quite cleanly with small throttle openings. Give it as much as half throttle though, and you can feel it do a bit of a hiccup at 2700rpm and the AFRs will momentarily go very lean (16-18:1). Next thing to try is go back to a 60F9 idle, which I think will address most of the hiccup, but at the expense of somewhat rich part throttle fuelling and perhaps lazier response.

 

Will post back with results...

 

Some interesting observations though...increasing the size of the mains does very little to fix the 2700rpm stumbles (even going up 3 sizes doesn't seem to make much difference). Going richer on the 'tube helps a little but not a lot. What really seems to fix the stumbles is jacking up the idle jet size, but according to the wideband, the idle jet has a pretty wide ranging effect, and still seems to affect light throttle fuelling even as high as 4000rpm.

Edited May 12, 2010 by Babalouie

[yetterben]

Some interesting observations though...increasing the size of the mains does very little to fix the 2700rpm stumbles (even going up 3 sizes doesn't seem to make much difference). Going richer on the 'tube helps a little but not a lot. What really seems to fix the stumbles is jacking up the idle jet size, but according to the wideband, the idle jet has a pretty wide ranging effect, and still seems to affect light throttle fuelling even as high as 4000rpm.

 

 

I try to tell this to people all the time. They never listen. They go buy the book. PAH!

 

rpm is not as relevant. Its velocity that matter's more. You can run off the idle till 6 grand and the mains wont come online. Lots of people with hicups need to throw the book out the window. Run a richer idle and don't concern yourself with oh no my idle mixture is only out 1/4 turn.

Edited May 15, 2010 by yetterben

[Babalouie]

I try to tell this to people all the time. They never listen. They go buy the book. PAH!

Yeah, this part became pretty clear with the wideband results. I was experimenting with 50, 55 and 60 idle jets, and you could clearly see the effects on part throttle AFRs, as high as 4000rpm on 1/2 throttle. I'm using 36mm chokes tho.

 

rpm is not as relevant. Its velocity that matter's more. You can run off the idle till 6 grand and the mains wont come online. Lots of people with hicups need to throw the book out the window. Run a richer idle and don't concern yourself with oh no my idle mixture is only out 1/4 turn.

Agree. But I think I've taken it as far as it can go with the jetting, and ended up with similar conclusions to yours. 60F9 on the idles has a little stumble but not a lot. Downside is very rich smelling running and lazy response. But a recent discovery is that what helps eradicate the stumbles even more, is ignition advance.

 

As little as 3 degs more static advance made a massive difference to overcoming the stumbles (and the AFRs went richer at 3000rpm too!...not sure about the theoretical reason behind it, but it did...). As an experiment, I cranked in 6 degs more static advance (18degs static) which meant that it pinged at high revs and so that was off limits, but the 3000rpm stumble point was smooth as silk. So the next step is to recurve the distributor to something more like 10 degrees mech advance, so I can run 18 degs static.

Edited May 16, 2010 by Babalouie

[yetterben]

Never had a stumble on mine tuned off wideband to idle at high 13's and 14.5 cruise 12.5 wot so many variables to tweak from floats to needles. I can make a weber bend at my will and give me a reach around.

 

Then i ran 18psi of boost threw them via a t04e

Edited May 16, 2010 by yetterben

[Lazeum]

since my last technical post, I've changed my head with Braap's custom P79 head & Rebello Street assymetrical cam grind. CR went from 10.3/10.5 to 9.3/9.5. Flow/efficiency of the head is now much better than my previous stock N42 head.

 

So it is now time to tune again the engine

 

So far, I've just spent time making the engine run, idle has been setup correctly. I had to get smaller idle jet than before.

 

My setup as of today:

40DCOE

32mm choke

45f9 idle jet

45 accel pump

135 main

180 air

F11 emulsion tube

 

Float height has been properly done and adjusted when carbs were out of car during head swap.

 

I wanted to try to setup the engine by using the original mech pump. this weekend I found out engine was running out of gas on high gears. So I've plugged my Electrical pump (Carter unit SUPER loud)

 

Before any comments on AFR, I can say engine is quite responsive, no stumbling, chasing or whatsoever. I can hit the throttle at low rpm, car goes quite nicely. Power is good but I'm sure it could be better. The Z is faster than my Dad's BMW Z3 with 3.0L L6 (231hp) to give you a comparison point.

However, Engine is smooth except when cold, choke is required to avoid the engine to stall. When hot, engine idle is set at 800rpm.

 

 

I've done some AFR log in 2nd gear, fuel pump should be out of the picture since there's not enough time to get fuel starvation with empty bowl. However, low fuel level in bowl could have an impact on AFR.

Fuel supply setup used is electrical pump next to the tank with still mech pump attached to the system followed by a fuel pressure regulator setup at 3psi.

I'm currently wondering if it could be a restriction in the system, it will be removed anyway very shorly so I will find out.

 

AFR were super rich in low/mid range & very lean in high rpm. So I've switched my main jet with smaller ones: 130.

Here's the log.

 

 

I'm quite consufed with the results. It means better head with high flow & better efficiency requires much less fuel than stock head???!!

I would have expected the opposite quite frankly.

Could it be the back pressure being so much greater that it makes the engine sucking much more fuel thru the same jets size?

 

I've been questionning the results from the wideband but the exhaust tip is really black.

Spark plugs however are brown. Based on the results, Main jet required would be in the ball park of 110/120. I've never seen an engine running such small main jets (I don't have a lot experience yet though). If my engine needs those to be happy I'll go with it but I need to source some parts then.Main jets would need to be smaller too to richen the AFR at high rpm, I've got 165 air jet to try. I'll see how it goes.

 

Regarding idle, it is also very rich at cruising speed, I run around 10.5/11.0 AFR whereas idle screws are 1.5 turns from being close.

since idle screws are fine and cruising AFR is super rich I'm wondering if I should not deviate from xxf9 idle jets and try something else with bigger air bypass hole (f6, f8 ?????) I need to investigate on this one.

 

It is also difficult to predict yet since AFR is not steady at all but it seems I've lost the rich spot at 4500rpm. Leadings me to think it is intake geometry related since carbs & manifold remain the same. (see page 13, post 312)

Edited July 5, 2010 by Lazeum

[Lazeum]

I've read if chokes (venturi) are too small, it could make the engine too rich no matter what   

 

What do you think about such remark?

 

Choke Tube or Main Venturi size is the basis for everything in tuning DCOE, IDA and IDF carbs. If you get the Venturis wrong you will never get it running right. Too big and you will always have a flat spot that you cannot tune...Too small and it will always run rich and not make any power.

 

The source; the text is on the lower section of the page above the choke size table.

[zredbaron]

the "no matter what" part is just stupid. you can always select mains to match the venturis. you'd just inhibit the engine's flow (and therefore power) potential if your chokes are too small.

 

case in point, your new engine out flows your old one. 40 dcoes in my opinion should only be used for entry level street performance L24s and L26s. any increased displacement / head flow upgrades require larger venturis to enable the increase in flow / performance.

 

simply stated, your engine is CHOKING for air. there is minimal air, which calls for minimally sized mains to balance it. go to 34-36mm chokes and rejet. your mains will be more normal.

 

if you want driveability, try the 34mm first. if you intend to compete with the car or just want the performance, go straight to the 36mm. the head you have probably can out-flow the 36mm chokes, but i don't remember what bottom end you have. if you have >= 2800cc block, with your new head i'd say go for the 36mm and call it a day.

 

you have likely upgraded your engine into an under-carb'd condition. welcome to the club.

[Lazeum]

 

you have likely upgraded your engine into an under-carb'd condition. welcome to the club.  

 

   I'm glad to be part of that club.

 

I knew choke would be too small but I did not think it would lead to such a rich mixture.

 

I run out of jets, 130 are the smallest I've got so next step would be shopping (or money to spend from another point of view) I might try smaller idle jet, I'll have to look for what I've got, I'm not so sure about my jet library.

 

The goal is to get a street car with a lot of torque, so 34mm choke would be my next step. If I have to go to 36mm, I'd rather go with 45DCOE, I beleive the ratio choke vs. carb diameter is important. 

 

As far as bottom end, I've got a rebuild stock L28 overbored to 0.5mm.

 

 

Edited July 5, 2010 by Lazeum

[zredbaron]

if you keep upgrading your engine and neglect to also upgrade from your 40 dcoes, your jet selection will go odd directions.

 

my overworked 36mm equipped 40 dcoes for example are fairly happy to be running 60f9 idles, 155 mains and 155 airs. in the colder months, it likes 165 mains and 145 airs. strange, but true.

 

currently idles at 14.5 on the wide band, WOT varies from 12.5 to 13.5 from 2k to 7k, *assuming* i properly feather the throttle pedal below 4k. i consider this about as close as i'll ever get, so i call it done. (i won't ever again attempt to tune to WOT for all rpm bands. not possible in my application, it seems.)

 

also, i found while tuning via wideband, i could actually tune to a specific gear. i theorize this was because the cold air intake w/box was actually receiving a small ram air effect. tuning for a higher gear (ie 4th) required a larger main than tuning for a lower gear. i thought that was pretty cool. since the car is a dedicated autocrosser, i tune it for 2nd gear.

 

we all like to hear each others' triples get on it, this local autox video was taken just yesterday:

Edited July 5, 2010 by zredbaron

[Lazeum]

Vid looks good with quite responsive engine

 

I'll think about what I want over the weekend but I want to keep a car with high torque at low rpm instead of max HP, of course if I can get both, I'll take it!

 

I could consider also 45DCOE. I'm located in europe so I guess it is a little easier. There're 2 new 45DCOE for 500€ for sale for instance now. However my intake manifold, a Cannon unit, has some runner that are smaller than 45 sio I'm wondering if it would make sense to go with them as straight remplacement from 40DCOE. So porting might help solving this issue though.