Post Weber Jet 32/36 & 38 Sizes + Venturi Sizes for DCOE

[garfunkle55]

ohhh, I've been looking all over weber sites trying to find some kind of jet or something. Thanks for clearing that up.

[enache]

Hi

I might be a bit off topic but I was wondering if anyone has any suggestions on the jet sizes for a 38 DGMS considering it will be on a Cologne 2.8l V6.

Thx

[2oodoor]

Hi

I might be a bit off topic but I was wondering if anyone has any suggestions on the jet sizes for a 38 DGMS considering it will be on a Cologne 2.8l V6.

Thx

I believe that motor came with a 38 (one I had did anyway) and oem jet sizes are published in the weber book, which I don't have handy at the moment but will post them here in a bit since that would be beneficial to us too if someone lucked up and found one in the junk yard.
Capri 2.8 early models...search MK3 performance maybe ..Mains 142, airs 185, idles 45, em.tubes F50, pump 55 is going to be close.

[2oodoor]

Ok this set up is not tested with a wideband but it REALLY woke up this DGV-5a 32/36 on an otherwise stock A20A1. This thing has a hellova relentless grunt now..no bog and pulls hard from a dead stop to full thottle through redline.
This is on a 5 speed car and I dont know how well this would work on an auto, not the pump jet anyway. There is some secondary enrichening there that may not always be needed but certainly has an exciting effect.

--Primary Main Jet = 150
--Secondary Main Jet = 140
--Primary Air-Correction Jet = 180
--Secondary Air-Correction Jet = 165
--Primary Idle Jet = 60
--Secondary Idle Jet = 50
--Accelerator Pump Jet = 70 dual outlet
--Primary Emulsion Tube = F50
--Secondary Emulsion Tube = F-50

[itzdave]

anybody got an recommendations on jet sizes for dual Weber 40 DCOE's? with a few other bolt-ons as well, if that changes anything...

[hondalude86]

He is the jet settings i was running without a wideband... def something to start at if you have basic mods.

Here is what I had mod wise... Delta 285 cam regrind. Bored out to 81mm S&S headers...

Accel pump jets, 45
Accel Discharge, 45 (took out my soldered closed discharge)
main jets, 140
air correctors, 200
emulsion tubes f7
idle jets 50f9

Ran like a bad out of hell with even super low compression in one of the cylinders. It even pulled my b16a prelude with these jets, and it didn't have any problems revving up... you know like when you initially get on it, no dead spots...

and that was with 40mm chokes

[Fixedit]

The Weber seems to be fairly sensitive to air temperature. I do have the hot water running to the manifold so it is being heated. I should mention though that I'm near Chicago and the temp has gone from below freezing to +70F since I started tuning, so I'm talking about a pretty large temp change. The choke also seems a little sticky sometimes, even though I've greased it a couple times. I only plan to drive the car when it's warm though so it's not a big deal.

C|

When I first ran my 38 I had no coolant hooked up to the manifold, and cold start warm-ups took ages. The carb really does not like to be cold, and just the temp changes from noon to evenings really affect the tune. Life’s a bit easier now with the coolant running through the manifold.

Regardless, tuning this thing has been a roller coaster. I finally actually understand the carb though, and I’m sitting at a good spot. Engine is an A20A1, modified intake manifold, 88-89 LXi exhaust manifold, 272 duration camshaft, Weber 38 carb.

--Main Jets = 127
--Air-Correction Jets = 200
--Idle Jets = 0.57
--Emulsion Tubes = F66

My mains may seem lean, but according to the AFR gauge it’s what the car wants. I might be able to run larger ones with a larger air corrector, but it’s the perfect mixture at WOT right now. It actually gets a little rich in the high RPMs wide open. But that’s the least of my concern. My biggest problem has always been partial-throttle lean out. Took me forever to figure out it’s because of the progression circuit, and even then it’s still been difficult to nail a good tune.

To get the perfect idle mixture AND proper cruise mixture (which by the way, Cygnus mentions the cruise mixture is controlled by the mains, I disagree. Changing my mains did nothing for cruise mixture, but idle jets changes it every time. That’s because they also control the progression/transition circuit) has been the biggest challenge. For a while I had 0.60 idle jets, as that’s the only way I could eradicate the lean spot, but cruise mixture was way too rich and mileage was bad (11.0 cruise, 200 miles from full tank). So I tried 0.55’s down to 0.45’s. 0.55 and 0.50, I could idle a healthy 13.8-14.2 with the idle screws 1 to 1.25 turns out, but the progression circuit (at cruise) would lean out from 15.0 through 17.0. So between the 0.55 and 0.60, it was either lean out at cruise or too rich at cruise. I’ve been pulling my hair out about it, and as a last ditch effort I ordered the 0.57 idle jets. Best I can say is it’s “better,” but not perfect. I think about 3/4 turn out on both idle screws. Cruise is closer to 13.5-14.2, progression circuit still leans out but only if RPMs climb (like if I leave it in 2nd with partial throttle at 30MPH) so if I just drive it right I can avoid it. WOT is perfect (14.5-13.5) until about 4200 RPM it hits 12.5. Which I don’t understand with the mains being as small as they are and the engine using a longer duration cam…but I do have a set of 125’s so maybe I’ll try those but I feel like I’m going to run into a different kind of lean spot if I keep going smaller. I don’t understand how other people are able to run such large jets even on a stock A20, like I know no engine is exactly the same but what the hell lol.

[ShiRen]

I dont know the inner workings of the webers too well, but it sounds like to me that you immediately pointed out a problem

Changing my mains did nothing for cruise mixture, but idle jets changes it every time.

Pilot jets should not have a significant difference on cruise operation because once the throttles are open, it creates low pressure in the barrels, pulling fuel from the venturi. It needs to do that because the pilot jet is not a variable flow, it just shoots fuel through the hole with the fuel pressure. So, dont compensate with the pilot jet, set your idle afr according to the Redline manual and dont touch it after that.
It would help to know: Is your carb new? What other jets have you tried? Are you in high altitude?
I would suggest getting this carb ultrasonically cleaned if it is not new. Reset the main jet to something normal like a 140. Set the idle.
Maybe this has something to do with the air correction jets, not familiar with them, but knowing that fuel flow out of the venturi is based on a pressure differential around it, maybe there is something up there, so there is very little flow at low throttle percent. Maybe the air correction jets are too large or the emulsion tubes need to be larger. As far as the lean out on accel, that might help, but the accel pump might need retuned after cruise afr is somewhere reasonable. Also, if you are in high altitude, try to tune it somewhere a few hundred feet lower if that isnt too far from home, it will be easier to find a baseline.

[ShiRen]

38 WEBER

38 DGAS
Idle Mix Screw: 0.75-1.0 turns out.
Both screws should be as equally balanced as possible.
More then 1.0 turns and you need a larger idle jet.
Synchronous carbs must use the same size idle jets.

38 DGAS
Bogging problem in the upper rpm?
Try F6 emulsion tubes and slightly smaller idle jets to change the fuel curve.
The emulsion tubes will bring the main fuel curve down a bit lower and allow the engine to use it when vacuum is at a decent level.
The upper rpm will lean out just a bit, if needed smaller air correction jets can richen the mixture.

* The 38 weber came with these jets on a different car of ( 2994 cc ) ours is ( 1955 cc ).
(38) JET SIZE x2 , except for Pump Jet

- 1.45 Mains
- 1.85 Air Correction
- 0.50 Idle jet
- 0.65 Pump Jet
- F50 Emulsion Tubes

You may want to make a collection of jets, remember this is a synchronous carb.
There are two easy ways to richen the main mixture
Air Correction Jets ( Smaller # = Richer Mixture )
Main Jets ( Larger # = Richer Mixture )
A lot of the times I see the Air Correction dropped VS increasing the mains to get a richer mixture.
In some cases the mains are the restriction and must be increased, the air correction may be left unchanged or increased.

Hi,
I just wanted to add my experience to the thread.

I built an A20 with a stage 1 triflow (Colt) cam and a mildly ported head. Comp ratio I estimate at 9.0:1
The carb is a Weber 38/38 with the following jet sizes:

1.42 Mains
0.55 Idle
1.85 Air Correction
0.70 Pump Jet
F50 Emulsion Tubes

Idle mixture screws are at 3/4 and 1.5 turns out. Need to try and equalize these. It runs pretty good but the O2 sensor indicates lean under light throttle. Going to try 0.60 idle jets next.

1/6/2007:
Equalized the idle screws to 1-1/8 turns out. No change. Put in 0.60 idle jets and adjusted idle screws to 1 turn out. The light throttle stumble got worse and the lean spot is bigger; strange. Going to try larger mains tomorrow.

1/7/2006:
Put the idles back to 0.55 today. Then switched the mains to 1.50. The light throttle stumble is gone and there is no lean spot. The O2 sensor says rich all across the board but overall it feels pretty good. Exhaust sounds a bit chunky so maybe 1.45 would be better for the mains. Will have to order them though. Could maybe try some smaller idles too.

2/18/2007:
Installed a wideband O2 sensor to get real AFR readings. Changed the mains to 1.47. Feels about the same. Cruise mix is about 14:1. Part throttle mix is around 13:1. Light throttle under load is lean but not too bad, maybe 15.5:1. WOT is still way rich, sometimes 11:1. Going to try larger air correctors next.

2/20/2007:
Bumped the air correctors up to 200 today. WOT is better but still rich if you jump on it. Going to try 210s next.

2/23/2007:
Went to 210 air correctors a couple days ago. According to the AFR gauge it looks like it leaned out across the board. Medium and heavy throttle are pretty good. Light throttle seems a little erratic, sometimes it's rich, sometimes it's lean. Throttle response is still good though so maybe it's ok.

4/20/2007:
Bumped the air correctors up to 215. Medium and heavy throttle are good, WOT is almost dead on 14.7:1. But now I'm starting to see the problem with light throttle. The AFR at just off idle is ok but as throttle is increased it gets leaner and leaner until about 1/3 throttle, when it jumps back down to 14:1. I'm pretty sure this is the main circuit all of a sudden coming in. This tells me that the mains are coming in too late and the idles are at max capacity. Bumping up the idle jets makes light throttle too rich, so the next step is to try different emulsion tubes to bring in the mains earlier. This makes sense with the F50 E-tubes since they have all their holes at the top half of the tube. The farther up the tube they are, the later the mains will come in.

5/4/2007:
The warmer weather is throwing a wrench into things. I tried some F6 e-tubes and they completely turned everything upside down so I went back to the F50s. So to fix the lean hole I raised the float level 2mm to bring in the mains a little earlier, and it definitely helped. But then the cruise mix was getting rather rich so I decided to try smaller idles (0.50) for once. And at the same time I dropped the air jets back to 210. And holy cow, it's nearly perfect! It's very lean on startup and needs some throttle feathering for the first couple minutes, but when it warms up it's almost dead on. Next I'm going to mess with the choke and maybe the idle screws some more to try and make it behave better on cold startup.

6/28/2007:
Made some more adjustments to compensate for the warm weather. Light throttle is a little too lean so it stumbles a bit, but I'm not going to mess with it anymore since I'm switching to fuel injection. So my current setup is:
1.45 Mains
0.55 Idle
2.10 Air Correction
0.60 Pump Jet
F50 Emulsion Tubes

This is a pretty good setup for warmer weather. For colder temps bump up the mains to 1.47 or 1.50.

C|

You arent anywhere near either of these setups... have you tried anything similar?

[Fixedit]

The idle jets meter fuel flow for the idle circuit as well as the progressive circuit. The progressive circuit consists of multiple passages right above the idle passage, which are activated with minute opening of the throttle plates (cruise position).

The carb is new, non-ethanol gas only. I have tried similar setups with rich results (which is what trips me up lol, since I don’t have a stock cam).. Since my last post I bumped up my mains to 135. WOT is too rich again but the lean flat spot is gone and cruise is about perfect. Despite all of that, this is the best tune I’ve had so far and I plan to leave it alone until necessary. At the point I want to try larger air correctors. Oh, and I’m right at sea level. I’m no carb expert but this is just what I’m experiencing. Having fun learning the 38 though