Weber 38/38 Jetting

Paul Wegweiser

Paul Wegweiser

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I've recently installed a pair of 38/38 Webers on my otherwise stock 3.0 E3...and after searching through the forums thoroughly, I'm curious to know what has worked for other folks using these on an OTHERWISE stock / 3.0 liter motor.

car ran very well with the 32/36 Webers, but I was hoping to gain a little more breathing at higher rpm...and while the 38s are not a magical bullet... I do think I'm seeing some decent results in improved throttle response and 70-90 mph full throttle / 4th gear pulls.

Some background info:

Carbs ordered without any "kit" so they had a fairly generic jetting installed. (Arrived with 145 Mains and 170 Air correctors) which yielded a very rich / bad flat spot with WOT / full throttle.

I have since installed 130 Mains and 185 Air correctors, which seems to yield great smooth performance throughout most of the rpm range.

I'm thinking the Mains could be larger - perhaps go back to 145s and add 200 Air Correctors... but if I don't see any real improvement in performance, why waste the extra fuel, right?

Anyone care to share their jetting on a STOCK / mostly stock 3.0 motor?

Any modifications suggested for sealing up unwanted passages? (I've heard of this mod on some 32/36 / M10 engine carbs)

Many Thanks!

The car gets better every single day!

Paul
 
Paul, for a rambling discussion of tuning these for a stock/tired 30, search for “ 38DGAS” where Steve and I talked Weber’s when I was setting up my 38/38’s.

If you have a pretty fresh euro engine, the extra carb capability might be helpful. I doubt it will provide a substantial improvement on a stock low compression USA spec late E9.

I should have access to my 38/38 equipped E9 this weekend and will post what I have in the carb after I refresh my memory.

Stan has these on his souped up 3.5l motor, but his setup might still be ok as a starting point.

Finally, I highly highly recommend getting a wife and AFM that you can stick in the tail pipe and go driving a with. It’s very helpful to know how far too lean/rich you are under different operation conditions, which you then translate back to the Weber setup parts (jets, air correctors, bleed valves etc).

John
 
Paul,

FWIW, in my 3.5 liter I'm running 140 mains, 180 air correctors, and 50 idle jets (though my last notes read I could have gone with 145's).

It took installation of an O2 sensor in the header to really dial it in, and then I was only successful after installing a Carter fuel pump (high volume, low pressure).

I've got a plastic case full of sorted 38/38 jets, so let me know if you would like to borrow it to dial your car in.

Jeff
 
Thanks John and Jeff!

I'm fairly well versed in Weber tuning, and even have an AFR set-up ready to go on the car (it's the one concession to modernity on my tii, and I have a "temporary" downpipe / wideband that I occasionally install when tuning customer 2002s.)

Motor is indeed a standard US spec 3.0.... although there's paperwork to suggest it's got a 3.3 bottom end. (I really should peek at the block to see if there's a donor car VIN on it, huh?) Head is tight as a drum (properly rebuilt 4.5 years ago - which was only 7000 miles ago) but there's certainly some tired rings in the thing. Oil consumption is about a quart every 700-800 miles during rather high speed interstate runs. Driving it like a mature adult yields MUCH lower numbers.

I've noticed a mild improvement and a slight change in where the torque seems to come on (it's a tad higher in the rpm range than the 32/36 set-up...and it spins better to 6000 rpm versus the 32/36 carbs as well. I've got the car as docile as it was with the 32/36 carbs... but once I see fuel mixture numbers I'll be able to play more with ignition timing and finer jetting tweaks. Throttle response is improved and the 70-90 mph in 4th gear improvement alone is worth it. FWIW: I generally dislike these 38s on M10 / 2002 motors for several reasons...but on the M30 they seemed more practical.

Among my reasoning for trying out the 38s, were sticking / tired secondary throttle shaft on one of my old carbs... the desire to go with electric vs water chokes, and weighing the pro/cons of rebuilding the old Webers or just playing with some larger fresh ones I can easily sell if I don't like them, with the long term intent of building a 3.5 bottom end for the car next year. My primary goal is to preserve the docile / easy to drive nature of the car...and so far I'm happy with it. No horrendous lag from idles to mains... no overly-touchy throttle pedal, etc.

Again - Thank you for the feedback! Once more jets arrive in my mailbox, I'll get deeper into larger mains vs larger air correctors...which may lead me down the rabbit hole of new idles for any new transition issues that crop up.

Cheers!

Paul
 
Hello,

I thought I would add to the pile having run 38s for years.
I went through my old Weber notes and found my 38's jetting notes. Though never ultimately fine tuned (on a dyno) I thought it was going pretty good for general road use.
(A dyno session likely would have changed a few things).

Mains: 145
Air correctors: 185
Pump jets: 70
Idle jets: 45
Em tubes: F50

Every motor is different, HTH.
-s
 
shanon said:
Hello,

I thought I would add to the pile having run 38s for years.
I went through my old Weber notes and found my 38's jetting notes. Though never ultimately fine tuned (on a dyno) I thought it was going pretty good for general road use.
(A dyno session likely would have changed a few things).

Mains: 145
Air correctors: 185
Pump jets: 70
Idle jets: 45
Em tubes: F50

Every motor is different, HTH.
-s
Click to expand...
Are these the carbs on my m30b35?
 
shanon said:
Yes, they are. Again, I don't recall if my notes we're my final set-up or a Weber base. You'd have to confirm by examination. I couldn't find a Weber 38/38 'stock/base' set-up in my books but a call to Pierce Manifolds should be informative.
Click to expand...
I’ll inspect to find out jetting. They have Ben running excellent as they are on this engine.
 
US Spec 3.3L w/Shrick 284 cam and dual 38s
  • Weber 38 DGAS Carbs - Jets: Idles: 60, Mains : 135, Air correctors : 200, Emulsion tubes : F50
  • Valve lash: A tight 0.008” measured at cam/rocker
  • Plugs: NGK BP5ES gapped at 0.032”
Runs about as good as it can throughout the range. Also using a 123 dist and can share the curve if needed.
 
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