Carter/Weber Jetting

[mrahc]

I found an old thread on this, but it was seven years old and inconclusive.  I'm wondering if anybody has successfully experimented with jetting on the carburetors that I'm sure most have bought from Tom Langdon (Carter/Weber, Weber 32DFT, Motorcraft 740, Motorcraft 5740, whichever other name they've been made under).  I purchased mine elsewhere, which at this point is starting to feel like a mistake, as the jetting is completely off from what should come from the factory and they aren't matched at all.  My current jets are as follows:

Front Carb
Primary Idle Jet - 70 (Stock = 50)
Primary Air Correcter - 150 (Stock = 160)
Primary Emulsion Tube - X04 (Stock = X05 or F53)
Primary Main Jet - 15 (Not sure if this is shortened from 115?)(Stock = 105)
Secondary Air Correcter - 150 (Stock - 220)
Secondary Emulsion Tube - X04 (Stock = T02 or F22)
Secondary Main Jet - 120 (Stock = 95)
Secondary Idle Jet - 60 (Stock = 60)

Rear Carb
Primary Idle Jet - 65
Primary Air Correcter - 150
Primary Emulsion Tube - X05
Primary Main Jet - 15 (?)
Secondary Air Correcter - 175
Secondary Emulsion Tube - X04 
Secondary Main Jet - 15 (?)
Secondary Idle Jet - 60

I was hoping somebody has been able to find parts for these carburetors, as I have had no luck.  I am going to plug and/or drill jets to the appropriate size, but I probably won't be able to accurately recreate the correct emulsion tubes. 

Just to add some additional information, the motor is a 230 and I am running an Edmunds water-heated intake and Fenton-style split manifold headers from Langdon.  The head was milled down .060" to bump up compression, but the cam and bore are stock.  The car makes a surprising amount of power, but is very inconsistent in its low-end performance and backfires some at idle.  I have a suspicion that the car is running too lean on the primary circuit, but it drives fine at steady speed and I don't hear any knocking.  Any help would be appreciated!

[Flatie46]

Usually if it back fires through  the carb it's a lean condition. If it's through the pipes it's rich.  Be sure to eliminate the possibility of an intake leak before tuning,

 

 

 

 

 

 

 

 

 

[raystewart]

I have zero experience on jetting these for that application, but tons working with Weber's.  Number one problem is typically too much fuel pressure, they like no more than 2 1/2 to 3 psi.  The float can only overcome the 3 psi, any more and you tend to go rich at odd times.   Number two problem is incorrect float level, they are very sensitive to float level. Fuel has to cover all of the holes in the emulsion tube, otherwise you get weird troubles that act like a small air jet will help.  We use to always start out with something in the area of 200 for air jets and 120 for mains and work from there.   Primary idle jet should run well with the mixture screw at 1 1/2 turns, if you need more turns out you should try a bigger jet, less turns, smaller.  Secondary idle jet is just about transition from primary to secondary, just about anything should work and some Weber's don't even have one.  You can usually make any emulsion tube work with the right combination of air and main jets.  

http://www.webercarbsdirect.com usually has all the jets and are good folks, local VW shops can often help too.   I can't imagine why you would want different jetting between front and rear carbs.  Best books ever on Weber's are " Weber carburetors by John Passini - Theory, Tuning and Maintenance ", hard to read, very "English", but the best info I have ever seen.   Some carbs have brass floats, some foam, watch out for a heavy float with foam ones, that can lead to hard to find troubles.   Do the two carbs have the same internal venturi diameters?  This is usually cast into the body on the outside of the throats, you should see something like 23 on the primary and 27 on the secondary, that is the internal diameter in millimeters.  If they don't match, I doubt you'll ever get it to run correctly. Also make sure they have the same auxiliary venturi sizes, that is the bar that runs across the throat with the tube in it.  They should be marked 3.5, 4 or 4.5, that is the minimum cross-section of the passage in the arm.  If they don't match you will be transitioning from the idle circuit to the main circuit at different times.   You will likely find more info on the DAT, DATR, DMTR series carbs which are very similar.  Hope this helps!  

[mrahc]

Flatie, I already checked for intake leaks.  Given the sporadic behavior, that was my first thought as well.  It usually backfires through the exhaust, but occasionally through the carburetor...thinking of it now, I should probably double check the ignition timing.

 

Ray, thank you for the information! I believe the venturis on both carbs are 22mm on both primary and secondary and the throttle bores are 32mm, but I have to check the auxiliary venturis for variation.  The different sized jetting is not intentional, but rather how they were set up when I purchased the carburetors.  I think I'm going to start with returning the jets to the sizes that I anticipated would be in them when they arrived.  It seems people have been happy with that setup in the past.  This isn't the only car we've got running Webers at the moment, and it certainly won't be the last, so I'll definitely have to look for that book.  Would you happen to know if jets and emulsion tubes are interchangeable between the DFT and the DAT, DATR, or DMTR?

[raystewart]

Yes, all of the calibrated components are interchangeable among those carbs.  Check out the weber carb website, you'll see the "base" part number for each jet along with the sizes that are offered and carb types to which they apply.  Weber's are really good carbs and infinitely tune-able.  I've installed them on countless domestics with good results as well as on the various imports I have owned through the years.  What part of PA are you in?  If in eastern PA are you aware of Harry's U-Pull-It?  I have harvested some jets from carbs there in the past for next to nothing.  

[mrahc]

I'm from the Wilkes-Barre/Scranton area. I've had some luck with parts at EZ Pull and Engler's, but I never thought to try Harry's for old cars. Looks like I'll be in the junkyards again this weekend!

[raystewart]

Well howdy sorta neighbor, I'm just below Stroudsburg.  The Harry's in Hazleton is huge and with those type of carbs used on so many cars you see them there at times.  You'll find them on a bunch of FWD cars from the 70's and 80's, perhaps even the early 90's.  A day at Harry's have never failed me, I always find something interesting, not always what I went for, but always something.  Good luck!

[Flatie46]

Not trying to hijack the thread but I've got a couple of Webber's a friend gave me several years back. I think they're DC03's if I remember. I was told they were the factory carbs from a Cosworth vega. I know nothing about Webber's but have worked on several other types over the years. Would these work on a 230 flattie? Like mentioned above I had read that they are very tuneable. 

[raystewart]

Those are likely DCOE's, which are a side draft carb.  If you can mount them you can make them work but even the smallest ones would likely be a bit much for a flathead. They made 38mm, 40mm, 42mm, 45mm and 48mm versions, even with small throats installed that would be a lot of carb for something like a flathead.  They have value to many import guys, you could probably sell them pretty easy and buy something a bit more appropriate.  

[Philmont 1968]

I realize that this reply is probably after the fact, however a good source for weber jets emulsion tubes and air correction jets is:

Pierce Manifolds  http://www.piercemanifolds.com  They have a good stock of parts and are very helpful; unlike Langdon's who is very unhelpful and gets defensive when you ask why they do not stock parts, or even have the information as to where to find the parts.  Not knowing the ins and outs of Webers, I bought two 32/34 DFT Webers (to go with Fenton intake/exhaust manifolds) from Langdon's and was very disappointed with their "it's your problem now" attitude.

That being said, I am now very pleased with the performance from my Chevy's 235 (bored out .080 and raised compression) Blue Flame Six.

Primary Idle Jet - 50
Primary Air Corrector -  160
Primary Emulsion Tube -  F22
Primary Main Jet - .115 
Secondary Air Corrector - 170
Secondary Emulsion Tube -  F25
Secondary Main Jet - .105
Secondary Idle Jet - 60