Weber 38 DGAS : info + settings + tuning

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ErikinSC

ErikinSC

Been there, done that, got the T-shirt.
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So, this is not a which carb is better thread. This is a new thread, and I will link to several other threads for those of us stubborn - committed - crazy enough to run a Weber 38 instead of a ______ carb.

Several other threads have documented some setup information, including Lean Best Idle Tuning, Jet recommendations based on elevation, and other info. I'm totally committed to fine tuning the Weber 38 that I have - and if you're interested in sharing your constructive thoughts - trials and failures - please join in. As a matter of fact - several of them are in the FAQs also.

Some great resources to start with :

The *** Weber Carb*** Adjustment Thread

Weber carb idle help

Weber carb and electric choke

The Weber 38 / Fuel Pressure Thread

The Weber 38 linkage help with pics thread

The Weber vs OEM Thread : located on the 60 thread...

A good Carb fundamental explantion website (it helped me understand) : http://www.datsun2000.com/tech/weber_tuning_methodology.htm
 
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My set up :

'74 FJ40 with a replacement 2F (sn 882263) and what I was told is the F head (steel valve cover). I have a stock exhaust header and intake, but the truck has been de-smogged. I have a Weber 38/38 with cable throttle and gas pedle setup (from TPI - installed by the PO). Non USA vacuum advance distributor, points & condenser, and an aftermarket coil.

I have a mechanical fuel pump, 4psi O/P with a @Weber Sarge suggested CJ style 'vented' inline fuel filter, just before the carb :

2015-04-04 20.48.51.webp


And I have the stock heat shield installed, less the insulator. I have a 2 piece aluminum mounting bracket for the weber, and Im holding 20in of vacuum.

2015-03-30 23.57.32.webp


I am using a Toyota Non-USA vacumm advance dizzy, new points, condenser and rotor.... timing bullet is on the top side of the mark (@ 8* BTDC) on the flywheel window.

Ive been having tuning issues - so I ordered a jet kit from Redline. I called Redline and because I am Sea Level, and have HIGH HUMIDITY, I asked for a baseline of which jets I should be running. They suggested a 50 or 55 Idle jet, Leave the Main Jets alone (I will ensure they are still 150's and he thought I might need to increase my Air Corrector from (it came with a 170) to the 190, 200 or even a 210 due to the high humidity.

I've got the carb idling at 525 RPM today, and going to test drive it and make some changes over the weekend.

What have you got your Weber 38 set up with for Jets - and Why?
 
Good start , giving all the baseline info stops confusion later when figuring out tuning . One of the main issues with Weber installs is that they do require a level of "tuning in" to make the carb work with the engine - no two are alike and the carb is sensitive enough to show it . I wish Redline and WorldPac would have researched more on cfm requirements for these engines as the 38mm carb is not enough - it should have been a 40-42mm running 28-30mm venturis and not the 27mm throats of the 38DGAS . The 38 works great on engines up to about 3.0L , after that it's just not enough cfm . I've modified a few for Cruisers in the past and opened the venturi's a lot (not recommended) and it does make a huge difference . A 40 DCNF would have worked a lot better and they have the option of installing various sizes of throats to better match vacuum/cfm demands . Not to mention they are a much higher quality carb using ball bearings on their throttle shaft . There is no choke , but instead the DCNF uses a "starting circuit" that is completely tunable and can use different size air/fuel jets and tubes . That model carb can be tuned to anything , my old Sami was running a 40DCNF with 28mm venturi throats on the 1.6L Tracker block / modified big valve Sami head produced 145hp @6200 revs . The DCNF would also solve most of the install issues on F series engines using a much simpler cable drive pedal or a bellcrank could be used to work with the stock solid linkage setups . I just never had time to try one and those carbs are pretty expensive - starting at around $500 . For this reason , despite my business in the past I do not recommend using a Weber on an F series engine - just too many shortcomings .

I'll help with tuning recommendations and try to help explain run issues so others can benefit tuning their own carb to fit their engine properly . These are not an "out of box" carb and must be dialed into the respective engine to make them run correctly . Properly setup , it should easily equal an efi engine in driveability .

Sarge
 
You should be able to save the .pdf into your pic folder or a temp folder, then attach file as normal. Use the 'attach file' tab under the text window on the PC. Not sure about from a movie device - unless you print and then take a photo of it.....
 
From @Weber Sarge : The Weber 38DGAS breakdown and parts list

The Weber 40DFAV breakdown and parts list

Parts List for Air Correction Jets, Needle Valves, Idle Jets, Chokes (main Venturis), Accelerator Pump Jets, Emulsion Tubes.... etc

An Engine application Data Table

EngineIDtable.webp
 

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Tuning Lessons learned :

1) Dont assume ANYTHING !

2) Check and set the timing :
image.webp image.webp
The 'red dot' should be lined up with the timing mark when the ignition is at 7º BTDC. It is strongly recommended to dot it with a white sharpie, paint stick or your wife's favorite red nail polish.

And while you are there, check the Points and set the Points Gap
image.webp Mine is .45mm (.018 in)

3) You've done good so far : now lets verify the spark plugs are in good shape and properly gapped :
image.webp

I have 2 different settings in the Haynes manual : USA 2F gets 1.0 mm (.039 in) and 'other models get 0.8mm (.031 in).... not sure why lets search that out :
 
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Additional documents supplied by @Weber Sarge :

Weber Initial Setup and Tuning notes - A MUST READ !

The Float Measure diagrams...

The Weber Troubleshooting Instructions

and an 18 page Weber Carb manual from Redline

Much thanks for sharing his printed materials :cheers: to assist those of making Webers our carb of choice (or necessity) :flipoff2:

Float measure all.gif
 

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I've got 4 huge folders of Weber info and at least 8 rare factory books here as well . I'd get them scanned and copied but Weber is pretty sensitive about copyright , and they know me - lol .

If anyone needs rare parts or odd jets , use this guy - he was my supplier for Italian Weber parts , not Spain or import crap , all genuine stuff and ships pretty fast/cheap ....a lot of nos stuff too .
http://stores.ebay.com/ALFA1750S-CARBURETORS-PARTS-STORE?_rdc=1

I have the original , archived "eye bleeder" thread from the Toyota truck Tech section of the old Offroad.com forum - one of the computer guru's got the archive from some obscure server and saved it - over 100 pages of tuning info and a lot of it applies to nearly any engine/carb combo and building things to work correctly . I'll email the pdf to Erik if anyone wants to go blind trying read/absorb all of it ...

Sarge
 
JohnnyC said:
These are observations and can be used as a base to start at:

Looking for real life applications for these #’rs

Weber cab jet sizes:

Main Jets 38/38:
Elevation:
SL (sea level) 1250ft 2500 3750 5000 6250 7500 8725+
F 150 145 140 135 135 130 130 125
2F 155 150 145 140 135 135 130 130


Air Correction 38/38:
Elevation:
SL (sea level) 1250ft 2500 3750 5000 6250 7500 8725+
F 180 180 185 185 190 190 195 200
2F 180 185 185 190 190 195 200 200

Idle jets 38/38:
Elevation:
SL (sea level) 1250ft 2500 3750 5000 6250 7500 8725+
F 60 60 55 55 50 50 45 45
2F 60 60 55 50 50 45 45 40




These jets in most cases go up incrementally 5 points…I have seen some odd in-between sizes 138’s 132’s ect.

(+/-) 5 points would be fine tuning from these points.
Click to expand...

@JohnnyC - did you fou find these to be fairly accurate 'baseline jet settings' ? I am at Sea Level, and wanted to 're-baseline' my carb before trying to make adjustments. I contacted Redline and they made a different suggestion about the Air Correction jet based on my relative humidity... Curious about your list above.
 
They are mainly from other than cruiser vehicles ... And observations from myself and a buddy of mine...

Are they telling you to use a higher air? Higher = leaner.. But... Our cruisers hardly are in the range for the air correction to make a big difference... They more critical in higher RPM ranges
 
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Be careful with that post - I've had complaints it's addictive and can cause blindness from folks trying to read all of it ....lol . A lot of the original baseline jetting tables are wrong at this point due to the ethanol and other changes in fuel quality these days . No one really makes a decent "kit" for anything other than modified high compression engines either . Generally , you can stick with the main fuel jet size and either drop one increment for the air corrector or increase one size to dial in the main mixture at cruise rpm's...
Sarge
 
Files from @Weber Sarge :)

http://www.trollholescruisers.com/tech/Weber Carb/weber/weber manual.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/walbro document.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/webertrouble.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/40DFAVpdf.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/40DCNFa.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/32.36DGAVpdf.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/38DGASpdf.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/float measure all.gif

http://www.trollholescruisers.com/tech/Weber Carb/weber/Thumbs.db

http://www.trollholescruisers.com/tech/Weber Carb/weber/jetapplications.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/calpart.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/32.36DGAVpartslistpdf.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/38DGASpartslistpdf.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/40DFAVpartslistpdf.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/40DCNFpl.pdf

http://www.trollholescruisers.com/tech/Weber Carb/weber/weber manual.pdf
 
JohnnyC said:
Are they telling you to use a higher air? Higher = leaner.. But... Our cruisers hardly are in the range for the air correction to make a big difference... They more critical in higher RPM ranges
Click to expand...

I've got my timinng set 7.5* BTDC (it was suggested I adjust it to 9-10 BTDC)
150 Main jet
200 Air Correction Jet (suggested by Redline to increase from 170 to 200 or 210 due to humidity in S Carolina)
50 Idle jets - Fender side is 1 full turn out, Engine side is 1-1/4 out (throttle linkage is on the firewall side)
Idle Speed is 1+ in (after contact) and turning about 500-525 RPM. Not quite the 650RPM, but I'd have to turn it in at least 1.5 turns....

It seems to be OK, but idling a bit ruff, where the rig noticably rocks gently while idling.

Plan -> Adjust timing first, then retune with current jets.
 
@Weber Sarge's 'eye bleeding Weber thread'
- everything you wanted to know, and more than you can remember...
 

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