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


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Hi all,

I was wondering if many of us would share our weber jet sizes vs different setup L series 6's.. Just to help others tune their weber fed ZEDs.

My 240z has the original block bored out to around 2.5l with a appox 280-288 degree cam or 74 degree depending on how you read them(tighe cams au-will edit with cam grind number later).

No porting- valve grind - 6,3,2 extractors 2.5 inch system.

Tripple webber 45's on lynx manifold running:

135 mains

155 air correction

32mm chokes

f2 emm tubes

35 accerator pump jet

f955 idle jets

"sock filters"


This setup gets me appox 21 MPG and revs out very hard above 3500rpm..

BUT is a bit coughy and sick up to 3000rpm which i think is mainly due

the "big" f2 emm tubes and the small 35 acc pump jets.. I also think that the 155 air corr jets is a bit small.

I hope to change the emm tubes to f11(or f15), the acc pump jets to 50's and the air corr jets to around 190-200..and i will post here when i do to show progress.

Anyone else wanta share their setups?

btw anyone else have any extra jets for sale in au(pm me!!)???

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I have 40DCOE triples on my 280. ported and polished N47 head. I bought my carbs from TEP out of callifornia (hate that place) TWM intake manifold. And stock however they had it setup.

about 20 mpg best on average.

pretty sure they have 38mm chokes

sorry this doesn't help much, but i'm lookn' to change out some stuff to get better street ability. mine don't kick in either fully till about 4. Also have a Nissan racing cam from japan.


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You should run an F11 emulsion tube, I found a performance gain running those. DOn't remember but I think the F2 is the really rich one, with no restriction in fuel flow, and if so, not right for your application.


On my 40 DCOE set up, with 33 mm chokes, I was running 155 mains, and 190 or so aircorrector. If it stubles off idle, go up a size on the pump jet.


Here is the "general" rule of thumb. Your choke size times 4 for a starting point on the main jet, and you main jet plus 40 for the air corrector. This should get you in the ball park.


Now for the fun statement. IMO, it mattes not what you have done to the engine, the carb is a fixed diameter, and only flows so much air, no matter what you have done to the engine. Once jetted properly, you should be able to move the carbs from your engine to about any L6 without issues. I could move mine from a 2.4 to a 2.8, with no adjustments, other then perhaps idle jet tweeking.


Man I envy you, nothing sounds finer then an L6 with side drafts.

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Awesome... carbs are fairly new to me, but i'm learning quickly. Any tips in jetting is greatly apreciated, i've only found a couple really useful sights for tunning webers, but the jets are so expensive i'm hesitant to try new ones.


(don't envy, the gas price kills me)

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ok so today i was cleaning my carbs and i had them off to wrap my header, and noticed on the venturi it was stapmed 30... now i was under the impression i purchased 38mm chokes.... so... is this still possible or? Little confused here, can i measure the choke?


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ok so today i was cleaning my carbs and i had them off to wrap my header' date=' and noticed on the venturi it was stapmed 30... now i was under the impression i purchased 38mm chokes.... so... is this still possible or? Little confused here, can i measure the choke?



I think the largest choke size avalable for the 40DCOE is 36mm. And yes you could measure the inside of the choke but as you found out they are stamped with the size.

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Is there a pattern to emulsion tube sizing? F2 is richer than F11 is leaner than F20? Or am I missing something there?


The emulsion tubes # also relates to where in the rpm range the engine gets more or less fuel (low rpm richer or high end richer, etc.)(but only 1 part of the big picture).

One of the best books I have found for weber tuning is Weber Guide To Parts & Tuning from http://piercemanifolds.com/accessories.htm

It is easy to understand and has lots of pics and part info / #`s.


Buy One! I think mine was about $20.00

I have several weber books, and this one tied it all together for me.

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Guest NapaBill

A couple of points with regard to Webers:


Emulsion tubes were assigned their number in the order in which they were created (F-1, F-2, etc) so there is no correlation between E-Tube # and characteristics. To really get into them you have to look at the blueprints that show the size and location of the holes. Generally, the more holes at the top of the tube the leaner at the top end, the more holes at the bottom of the tube the richer at the top end. As I recall, F-11 or F-16 should be about right for a Z, although I would run 40 DCOE's on the street, not 45's


You didn't mention the Auxilliary Venturi size. That's the "bombsight" looking piece that fits on top of the Main Choke (venturi). A smaller A/V will allow the main circuit to come in sooner, helping with the idle-to-main transition. I would suggest 3.5 A/V in a street Z. The 45's probably came with 4.5's.


The most common reason for Weber-equipped engines to stumble or lag below 3000 rpm is incorrect throttle plate adjustment. The throttle plates should be set so that they cover the transition ports which are just above and upstream of the throttle plates. Typically, someone has screwed down the throttle plate postioning screw to "adjust" the idle. When that is done, fuel is drawn from the transition circuit during idle, which results in a lean mixture as the throttles are opened. (The engine is probably running rich at idle as well.) The cure is to adjust the throttle plates correctly, either by looking through the progression port holes which are visible under the large flat-head brass screws on the top of the carbs near the mounting flange, or by removing the carbs from the manifold and setting them before installation. Once those are set, all idle adjustments are done using only the idle mixture screws. Bear in mind that Webers are designed to work from the idle circuit up to around 3000 rpm when the transition to the main circuit is complete.


A couple of other minor points: changing main jets will affect the mixture over the entire rpm range from about 3000-up, whereas changing the air corrector jets mainly affects the mixture at the high end of the range. So if you are rich at the top end and OK at the mid-range, go to a larger air correction. If you are lean all the way from 3000-up, go to a larger main.


Finally, don't waste your money on pump jets. They are a very small part of the overall operation. More effective (and cheaper) is changing the accelerator pump bleed-back valve in the bottom of the float bowl. You can reduce the size of the bleed-back so that more fuel goes through the pump circuit. You can even put in a 0 valve so there is no bleed-back. But again, if everything else is right, you really shouldn't have to mess with the accelrator pump circuit.


This information comes from a couple of lifetimes ago when I was in charge of R&D for the (then) sole US importer for Weber Carburetors, doing the prototypes for new installations.



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Thanks for posting NapaBill and welcome.


Folks the man knows what he`s talking about!

The book I mentioned above shows all the e tube configurations and has a chart showing just what NapaBill was saying (as well as alot of other info).


Buy The Book :D

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Guest NapaBill

Aw, shucks, guys! :oops: Thanks.

Fixing that throttle plate adjustment is the most important single step in getting Webers working properly. And I should have mentioned that Dat should get better mileage afterwards also.


This all stems from the fact that air is lighter than gasoline, so when you first crack the throttle air starts moving faster than the gasoline and the mixture goes lean. Weber compensated for this by placing the transition ports just upstream of the throttle plates so that more emulsified fuel could easily be sucked into the airstream at a high-vacuum location. If the throttles are set too far open at idle, the engine will pull the extra fuel from the transition circuit resulting in a rich idle and a lean off-idle condition. A carburetor mis-adjusted this way will usually show v-shaped areas downstream of the transition ports where the extra fuel has washed away the normal carbon deposits.


If you get everything set correctly and find that the mixture at idle is good but it is still lean off-idle, you can reduce the size of the air-correction in the idle jet (the F-#). Dat reports running 55F9 idle jets. Unlike emulsion tubes, the F-# on idle jets is progressive. It's been a long time and my memory is a bit fuzzy on this, but I believe that the lower the F-number the richer, so a 55F6 would enrich the transition circuit without seriously impacting the idle.


If you want to bring the transition to the main circuit in even earlier than the smaller A/V's will do, the answer is to go to smaller main chokes to boost the air velocity and thus increase the vacuum. This will make the engine more responsive in low and mid-range while reducing power on the top end.

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So... the butterfly is going to block the second port or be infront of it? What exactly is the proper way to set this throttle plate. Gonna try and do it this weekend.


Also... sorry for my stupidity early on the choke comment. Got some part names confused with other parts and bad information.

I have 30 mm chockes as mentioned, and after this weekend i'll prolly be able to tell you what some of the jets are when i take it apart.



Forgive the EFI guy :roll:

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  • 2 weeks later...

Ok, sorry this took so long, but my job does pay the bills.


Ok... triple weber 40 DCOE setup


TWM intake manifold

4.5 Venturi

30mm chockes

on the main jet... going from the top to the bottom of it:




Then i guess.. secondary jet ? right next to the Main jet in the housing

reads.. 45F9


Then there is another one about mid carb on side of houseing, I unscrewed a cover bolt with rubber o-ring, then under there was this jet i guess... was stamped 40


Let me know if you want some pics.. i took some with the macro on my camera.


Now as for this adjusting of the throttle plate... when you remove the nut and look down... i see three holes, so does the butterfly cover the middle one and leave the other two open, or cover the one closest to the manifold?


LIttle more info here would be apreciated.


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so i guess that is

30 chokes

200 air correction

115 mains

f11 emulsion tube

45F9 idle jets

and 40's accelerator jets


So how does it run? Any flat spots?

115 mains sound a tad lean but maybe mine is just a tad rich?



Ive finally got some f11 emulsion tubes on mine, but havnt changed anything else though. It has made a HUGE difference, it is much easier to drive. It is now sick below 2000rpm not 3000rpm and i put that down to the big cam(ie very little brake boosting at 1000rpm idle due to low vacuum).. And now it "SINGS" above 4500rpm .. The extra power in the L24 and the amazing sound(both exhaust and induction) is incredible.

I've been driving turbo 4's for a long time now and they sound crap vs my old datsun 6.

Thanks for all the advice(when i change more i'll post here)

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Guest NapaBill

The throttle plate should cover the progression port closest to the intake manifold so that the fuel from the idle jet goes through the opening with the tapered, spring-loaded mixture screw only. (The word "only" is used in a relative sense, because there is going to be some fuel going around the butterfly plate along with the air passing through). Your goal is to have that last progression port lined up with the center of the edge of the throttle butterfly. Then fiddle with the mixture crews, then idle jet and idle air-correction (the F# on the idle jet).


As an aside, there were some Webers that had small wedge shaped recesses or notches on the down-stream side of the throtle plates in order to bring the transition circuit in slightly earlier on larger displacement engines, but not before the throttles started to open.


Once the plates are set, I would (gently) screw in the mixture screws until they JUST bottom, then unscrew them 1-1/2 turns. If you can't get the idle right between 1 turn and 2 turns, you should change the idle jets: smaller if you need less than 1 turn, larger if you need more than 2 turns.


I think Ed's 115 mains and 200 airs are closer to what the engine needs than your 135 mains and 155 airs. I would expect between 115-125 for the mainsand around 200 for air. Of course a good dyno man could really nail it down.



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Well i tried tuning it the way you said.. but i guess i miss interpreted, i put the butterfly just infront of that last hole, and started it up. ran pretty good so i got out my color tune tool, to adjust the mixture. When that was all said and done it was idling about 2k. maybe a little higher, so disobeying your instructions i used the throttle plate screw and closed off the throttle plate till the idle kicked down. Which lead to whole world of other problems, including the throttle hanging, brakes nor workn' , etc.


So i shall tune again tomorrow and not use the color tune tool.

Keep ya posted.


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