Jump to content

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


Recommended Posts

  • 2 weeks later...
  • Replies 837
  • Created
  • Last Reply

Top Posters In This Topic

  • 4 months later...

Today I finally got around to using the Franck Fixture to drill the extra Prog ports.

I used the hole corresponding to +1mm closer to the engine and by watching the wideband it seemed to get rid of the thin spot (15+afr).

Only problem is it can make that spot a little rich now, but I will deal with that later. Can close the old hole or move the new one depending. The thin spot was a problem on track since the throttle response got wonky at times when I really needed some light and steady power.





Link to comment
Share on other sites

I have been MIA with a similar thread with DCNF downdrafts. There are many issues in common with DCOEs and most of what I wrote was based on Keith Francks observations and my previous modifications of weber DCOE 42 -9 carbs on my 240z.




Durrag,  the size of the furthest progression hole from the engine will influence the richness of the initial hole/s, and it may be easier to slowly enlarge this hole as a "dynamic air bleed" than to fill in or wire the 2nd progresson hole.





Link to comment
Share on other sites

I have been MIA with a similar thread with DCNF downdrafts. There are many issues in common with DCOEs and most of what I wrote was based on Keith Francks observations and my previous modifications of weber DCOE 42 -9 carbs on my 240z.




Durrag,  the size of the furthest progression hole from the engine will influence the richness of the initial hole/s, and it may be easier to slowly enlarge this hole as a "dynamic air bleed" than to fill in or wire the 2nd progresson hole.





I think that would lean out the entire circuit though, including the idle needles which are already a 65f9 drilled to a 73 on mine with the needles 3.5 full turns out.

What I would really like is to machine out the entire progression well, machine a key slot and then machine inserts which I can drill and modify at will, pull out replace and try a different setup.


Since it is a track only car I'm mostly interested in WOT though, so that won't happen.

I'd do some sort of ITB EFI before I did that.

Link to comment
Share on other sites

  • 1 month later...

hey guys, ill try to keep this short... picked up a 240z with L28 (stock N42/N47) and triple webers that wasnt running last year. im new to carbs and distributors (lots of time with EFI cars) i spent a LOT of time reading up and fighting with electrical gremlins but never quite got it going before winter hit. so ive been getting suspension in order and will be diving back in on the engine in a week or so. i also did a mild refresh of the carbs (cleaned out, replaced gaskets). the jetting seems quite a bit different from most of what ive been seeing in here, so i am somewhat skeptical that they were pulled off a different car and slapped on here - and based on what ive found on the rest of the car now that wouldnt surprise me in the least. during the rebuild i found a booster venturi that was in backwards, a broke off needle valve, binding throttle plate rod, etc... suffice to say, not confidence inspiring.


im just hoping to get some general input on the setup, because from the research ive done the jets sound huge for these motors. mostly because if it seems way off id like to get them sent off for a professional rebuild and all new jetting now. if it seems decent enough ill wait and give it another go. i do intend to use these in the long run but am also heavily entertaining the idea of slapping some SUs on in the name of getting on the road and getting to some track events. i have some local people familiar with them but nobody really comfortable with webers.


so, what do you think? thanks very much for any input in advance.


·        Stock N42/N47 L28 with triple Weber 45 DCOE 152 (w air bypass)

o   45 booster venturi

o   36mm choke

o   45F8 idle jet

o   170 air corrector

o   F16 emulsion

o   165 main jet

o   45 pump jet

o   40 intake discharge valve

o   Changed fuel inlet needle valve from 175->225 (one of old was bent and new ones came with rebuild kit)

Link to comment
Share on other sites

For me, the F16s never panned out.

I had 165s on a seriously ported huge cam 3L race motor, after it tossed a rod I installed my 2.8 N42/N42 with flat tops and a mild cam and needed to go down to 145 mains.


Get a wideband to really make it easy.

Link to comment
Share on other sites

DIdn't know this thread was still going!


Stock L28 N42 head/Block
83 280zx non turbo distributor mated to msd 6al, Don't remmeber the timing off hand.



Sanyo kiki 45 TWM units with weber jetting tower

Sanyo kiki intake manifold
 36mm inner venturi

 4.5 outer venturi
F11 emulsion tube ( soon to try F2)

145 main jet

185 air jet

F9 60 idle jet   Oer/sk version
50 Pump jet     Oer/sk version


Car runs well , no major poping/bucking, smooth transition and smooth revs to 6000 rpm.

Idle seems high, about 1300 rpm ( read that's Normal?)I think it may have something to do with my 240/280 tach conversion for the msd. My roomate is running the same setup and has a dead even idle at 900rpm, I'll know for sure once I get an aftermarket unit.
my jetting will differ soon as I'm finally gonna install my blowthrough turbo setup I'll post up the results if all goes well... or catastrophically wrong lol.




Link to comment
Share on other sites

  • 4 months later...

Just to give some updates and also to try to get new ideas from members in order to solve my problems with my setup.


A quick summary: since I've got my motor running with head made by Braap with Rebello "Street tight lash" cam, short block fully rebuilt by myself and distributorless Megajolt/EDIS ignition, I've never been able to eliminate some lean AFR at high rpm.


My carb setup is as follow:

40DCOE18 with ported Cannon manifold on the carb side, enlarged at head side but still smaller than head ports.

Main 135

air 180

F11 Etube

34mm chokes

4.5" aux venturis

45f9 idle jets

45 accel jets with 0 bleed valves

200 Needle jet


Car is very responsive, pulls hard. It is very smooth to drive at all rpm. I can floor it (fast to some extend though!) in 3rd gear at 1200rpm and engine just goes with no problem.

I'm basically missing only some hp at high rpm (too lean) where I can feel torque getting down around 5000rpm whereas it should go up to 6000rpm, as well as at mid rpm, being too rich.



So I've tried to use systemic approach (fishbone/Ishikawa method) to my problem and eliminate one by one every problem I could foresee.


Undercarbed intake:

I've played with choke sizes, between 32mm and 34mm. It did not change anything. I consider undercarb situation not the cause of my problem (even if I need 45DCOE :) )



Carb tuning

I've played with jets:

- Main jets change the entire AFR curve. Lean spot becomes richer but AFR at mid rpm becomes also very rich. To be at 15:1 AFR at 6000rpm, I need to be at 11:1 at 4000rpm.

- Air jet does not change anything at high rpm. I've been as small as possible (165), I ended up with engine cutting/starving fuel in tight right corners with no positive side effects.

- Idle jet does not change anything either.

- I've tried to plug the top holes on my F11 etube, I haven't observed any change at all.


here's the curve with current setup during Etube test:






Fuel supply NOK

- I've changed fuel pumps from Carter unit (@3.5psi) to Mallory unit (at 2psi - for some reason I could not go higher)

Result was some AFR translation, the AFR trend across rpm range was the same. As soon as I've changed main jet to get back to reasonable level, curves were similar. Fuel pump is not the cause of my problem.


- Fuel lines

Could some lines being clogged? I've changed all filters by new units, no change. Fuel tank has been cut open in 2, sanded, welded back together and it has received a full treatment to avoid corrosion.

I've installed a fuel pressure gauge on my dashboard; fuel pressure is steady across all rpm range, including at red line. So I've put fuel supply at carbs out of the picture.


- fuel bowl level.

It is exactly the same for the 3 carbs. I've got 25mm from the top of the carbs cover to the fuel level. To check that, I keep cover on, remove etube and use a straw/tube from a can of WD40 that I deep into the carb while plugging the other side with my finger. Everything is spot on.


- Fuel filling

I've increased the travel of the floats to make sure needle valves were fully opened with fuel level being very low, it did not change anything.



Timing NOK

since I can play with timing I thought I might be so off timing could be a reason.

I was running 34° max, I've tried 30° max, I've also tried 36°. There was no change at all on AFR curve. I've put timing out of the picture.




So I start to be short on ideas. Something is not ok and I don't get it.

Test on Etube seems to lead to some issue with fuel level, no change with clogged top holes tends to let me believe fuel does not go high enough around etube at WOT.

So next test would be to try bigger needle valve, even if 200 seems quite big already.


I also suspect the machine work I've done on intake. I've "just" enlarged the intake mostly at carbs side. Intake ports were smaller than carbs so I've made sure no step would stop air/fuel mix. Maybe I've made a thin/wide/thin condition leading to my problem. However, fuel and air are already mixed at that point, it would not explain why the engine runs lean.


So.... what am I missing??? I need fresh minds to propose some new ideas.


...and thanks for the ones who read everything  ;)

Link to comment
Share on other sites



Its weird for sure. For me I can make the slightest change with a choke 1 size up/down and everything has to be redone.The fact that your changing these things even timing, and not seeing a change is suspect. How old/new is your AFR sensor? Could it be bad? My problem is opposite of yours. If I want HIGH RPM, with good afr, I need it rich really down low. The Idle jet on mine 65F9 is perfect with 13-14 AFR never below or higher but Im running DCOE45's. 


According to my Dyno sheet from Rebello, I think I have the same cam (63di?) as you from the sounds of it. My 3.0L engine, has peak torque coming on at 5200 with max HP at 6500 rpm (how can HP go up and torque go down? Doesnt torque make HP?). I agree with you about the torque should be all the way up through the top. Why it dies out I dont know. Maybe its the design of the cam or something...I still plan to play with etubes some more to see if there is any change, it just gets expensive 90$ each time I want to try another etube. I have 4 right now, F2, F7, F11 and F16. Im running F11 like you.


I do know those 40's are a light on the top end, where as the 45's carry well up into the high rpm ranges. I would be more concerned on why you changing chokes, timing, jets and you dont see a change.... mine is so sensitive you sneeze and its different on the afr gauge. Thats what I would investigate first.


Just throwing it out there but my setup as it stands now (as rebello dyno'd):


Main 165

AC 200

Etube F11

Idle 65F9

38mm Chokes


00 bleed

Edited by AZGhost623
Link to comment
Share on other sites


When I say, there is no change, I meant after retuning. Of course, each time I change something around carbs such as fuel pressure or choke size, I have to review jetting. Once it is setup, I always end up with lean AFR at the same rpm range.


I'm also suspecting AFR tool.

In the mean time, I've lend my sensor to some friends who were able to use it successfully with no problem (besides the ones they were trying to fix - and they both did! (injectors for one, fuel pump for the other, both on s130)


- I've also changed my exhaust with the engine. So, exhaust has been also part of my investigation: no leak found, only tubing and tip have been changed. Exhaust manifold and muffler remain unchanged. I've added an intermediate resonator to lower noise level.


- I measure AFR with Innovate exhaust clamp at exhaust tip, maybe something to investigate. I could add a copper tube to the clamp to get some gas deeper from the exhaust to avoid any potential wave reversion issue plausible.


AZGhost623, you haven't said what are the needle valve you're running with your setup? Are they 200?



Regarding Didier's commment... no comment!  :)

Edited by Lazeum
Link to comment
Share on other sites

Whatever the stock needle valve is on the 45's ... I have not changed that part out.


Hmm maybe because your reading it at the tailpipe, it can continue to burn off on the hot exhaust tube/muffler? My O2 sensor is installed right after the header on the collector which is where it said to install it. Im using one of those AEM Wideband UEGO setups... Do you not have anything to measure on the car while you drive it, or is this all being done on a dyno? How are you putting load on the car while you test it out?

Link to comment
Share on other sites

  • 2 weeks later...

I thought I'd answered your message :/


Regarding my way of doing it is with a clamp made by Innovate. So I drive my car, go at WOT, steady/cruising operation and I record everything while driving. I can put my car on load, record and analyse everything quietly on the side of the road with the laptop. I can change jets along the road and go back. Same goes with timing, I analyze things out, change timing and go for trials.


I'm going to order needle jets and see if that could change anything.

Edited by Lazeum
Link to comment
Share on other sites

I'm not sure if I mentioned this to you already, but a couple of things come to mind here as possible issues.


On the AFR graph, you show AFRs of leaner than 21:1 up high on the unplugged tube curve. The car absolutely would not pull at all cleanly at those ratios. So the ratios are suspect in themselves.


This can be caused by a dying sensor, and/or a partially plugged tailpipe probe. I too use an Innovate tailpipe probe on my dyno, and it occasionally requires cleaning inside.


The other possibility is a dying sensor. Since you use a tailpipe probe, the exhaust is cooler and the sensor, even with its own heater, is more susceptible to damage from water. There is not much water in a cold exhaust up where an O2 sensor is usually mounted, but in our cases, any condensation in the entire exhaust goes past the sensor. This can kill them fast.


To minimize this problem, I suggest thoroughly warming up the exhaust and drying it out before attaching the tailpipe probe and sensor. It may be too late for this sensor though.


A dying sensor combined with a partially plugged tailpipe probe would show as spiking lean off the charts as a function of exhaust flow. In other words, it would seem normal up to a given HP level, then spike lean with no corresponding drop in power or smoothness.


To do it right, I would suggest having a threaded bung welded in to your collector, and install your sensor there.

Link to comment
Share on other sites

Oh, yeah, and power will continue to rise with RPM only if RPM is going up faster than torque is dropping.


100lb*ft at 5000RPM is 95.2hp.

83.33lb*ft (100 divided by 1.2) at 6000RPM (5000 multiplied by 1.2) is 95.2hp.


So, above, torque is dropping but power is not.

Link to comment
Share on other sites

Your point regarding probe being partially clogged could be something to doublecheck. That's a good point :)

I always run the car until it is fully warmed up prior to plug my sensor. However, I've lent the sensor to some of my friends, not sure they followed the same procedure.


Anyhow, sensor was working well for them with no lean reading at high rpm and I've always experienced off the chart lean reading while at idle at speed, even when sensor was brand new.

For the record, I also always calibrate the sensor before any session. 




To do it right, I would suggest having a threaded bung welded in to your collector, and install your sensor there.


This is obvisously something I should have done but it requires to drop the full exhaust. I could do it but it is a major pita; it is customed made, every section is spot welded to avoid it to become loose. Maybe something to think about in the future...

Link to comment
Share on other sites

All Right guys, I installed a wideband sensor with a gauge to read the AFRs. I need some help interpreting the results.


Here is the setup

stock 2.8L

180 air

F11 E tube

145 main

55 f8 idle


34 choke


Before the install the car idled right at 1000 rpm, on acceleration there was some lag.


The AFR readings:

first thing I noticed was that the car idled at 2000 rpm now, I do not understand why. Any thoughts? The sensor is mounted on the exhaust manifold after the 6 collection tubes merge into 1.

Idle and cruising AFR is between 10 to 11.

Hard acceleration is up to 15


So, what are some recommended changes I can make to get a proper AFR reading? Thanks

Link to comment
Share on other sites

You should try xxf9 idle jet, they work much better than f8 units on L engine, at least on "old" Italian DCOEs (40DCOE-18). I would try 50f9 instead. It should help to get better acceleration too.

Make sure your timing is ok. Too low timing would make the engine lazy and would create bog during acceleration also.

Check also the jet deep inside the fuel bowl. Mine are closed with solder, they are 0 bleed jet to get the most fuel possible during accel.


34mm choke on stock L28 is on the high side. I had much better results with 32mm without compromising top end power while tuning some friends' stock L28.

I'm running 135 & 34mm chokes with my tuned L28 engine and it is very rich, around 11:1 AFR (at least before engine run out of fuel in high rpm)

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...