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Technical Carter WCFB tech

Discussion in 'Traditional Hot Rods' started by carbking, Dec 15, 2013.

  1. carbking
    Joined: Dec 20, 2008
    Posts: 3,158

    carbking
    Member

    A couple of members asked in a different thread for a thread on WCFB tech.

    I will start the thread with some basic information, and monitor the thread. I will TRY to answer questions not answered by other members.

    General information:

    The Carter WCFB is one of the first generation of 4-barrel carburetors, with the first production WCFB being number 894s used on the 1952 Buick 70 series.

    From 1952 through 1967, Carter produced 214 DIFFERENT type WCFB carburetors for use on engines of displacements from 241 CID through 440 CID; thus there are several different air flow versions available. Carter did NOT publish CFM ratings (at least to my knowledge) on any WCFB carburetors. CFM ratings you see on the internet are either guesses or flowed by some third party. ALL of the type WCFB carbs were released as either O.E. (original equipment) or O.S.E. (original service equipment). There were NO aftermarket WCFB's produced.

    The first WCFB's have the almost square (3.75 x 3.875) mounting pattern. This was changed to the so-called "Carter rectangular" pattern over a few years in the 1955, 1956, 1957, 1958 time frame depending on manufacturer requirements.

    The first WCFB's had idle circuits on both the primary and the secondary systems. This feature was eliminated in the mid-1950's as being not one of their better ideas.

    MOST of the WCFB's used Carter's auxiliary air valve technology to prevent secondary flow until the engine air flow requirements were sufficiently large to use the secondary. Due to demand by Ford (and a very few Chrysler), Carter produced a few WCFB's with secondary diaphragms and no air valve. After a couple of years, Carter refused to produce this archaic design further. (Opinion) these units should be avoided except for those building number-matching showcars. They were less than reliable when new, and still less than reliable.

    Selection and tuning:

    The best time to do successful tuning for any aftermarket application is BEFORE the carburetor(s) is(are) actually purchased. Determine exactly what type application you want (looks only, high performance street and looks, race only), the engine displacement, the transmission type you will be using, and the mass (weight) of the vehicle you will be using. Using this data, try to find carburetors that were used by the factory on similar applications (believe it or not, engineers do things for a reason!!!).

    To do this research, you are welcome to use my website, as ALL production WCFB carbs are listed by identification number to application.

    Carter produced individual pages (2~8 pages per carburetor) that listed specifications and part numbers for the carburetor in question. These can be acquired, either through ebay or elsewhere.

    Carter also produced a circuit manual (about 8~10 pages) which describes each circuit of the WCFB in detail. Originals are scarce, but authorized reprints are available.

    Tuning a WCFB is similar to tuning the newer AFB. Most of the WCFB main metering jets are interchangeable with the most common of the three types of AFB main metering jet. Some of the AFB vacuum springs may also be used. Metering rods are totally different. All of these parts for all models of WCFB are available mail order (local procurement is probably a different story, depending on where you live).

    One other caviat on the purchase if you are planning to use these in multiples: CARBURETOR CFM IS NOT AN ADDITIVE PROPERTY! Two 500 CFM carbs on the same engine is NOT 1000 CFM. Depending on the state of tune of the engine and the efficiency of the manifold, somewhere between 700 and 800 would be a reasonable guess.

    The best advice I can give is to do your homework BEFORE you buy.

    Ask questions here, or 573-392-7378 (9-4 Mon-Tues central time).

    Jon.
     
  2. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,912

    dirty old man
    ALLIANCE MEMBER

    subscribe!!!!!!!!
     
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  3. AHotRod
    Joined: Jul 27, 2001
    Posts: 11,542

    AHotRod
    Member

    As always Jon you do such a great job in explaining these things.
    Thank You!
     
    Last edited: Dec 15, 2013
  4. carbking
    Joined: Dec 20, 2008
    Posts: 3,158

    carbking
    Member

    One tip that may keep someone out of trouble is float interchangeability.

    Carter engineers determined that different fuel levels were optimal for different applications. The maximum buoyancy (force) exerted by a float occurs when the arm of the float is perpendicular to the valve just when the valve seats. To maintain this maximum buoyancy with different fuel levels, Carter designed floats with the arm soldered onto the pontoons at different heights. Thus floats that LOOK the same MAY actually be different.

    When interchanging a float from one WCFB to another, ALWAYS set the two floats on a flat surface and measure the height of the surface to the arm where it is soldered to the pontoon. Incidentally, this tip crosses over to the Rochester 4-Jet.

    Jon.
     
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  5. bchctybob
    Joined: Sep 18, 2011
    Posts: 3,252

    bchctybob
    ALLIANCE MEMBER

    Just found this thread. Great info, especially the float geometry differences. Once again, thanks Jon.
     
  6. Rigley
    Joined: Apr 21, 2013
    Posts: 2

    Rigley
    Member

    Sounds like a lot of tire kicking to find the right carb, especially if I don't even know what I am looking for. I'd like to add a 4 bbl to my stock flatty with headers and a sbc distributor. Could you make any suggestions?
     
  7. I've got a sweet 56 vette intake with 2 wfcbs can't wait to get them fresh. Makes me wonder about the carbs. Goes good with the 2 x 4 thread. I know what I like. Blowers.
     
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  8. woodbutcher
    Joined: Apr 25, 2012
    Posts: 3,269

    woodbutcher
    Member

    :D This will be a most helpful thread.Thanks Jon.
    Good luck.Have fun.Be safe.
    Leo
     
  9. carbking
    Joined: Dec 20, 2008
    Posts: 3,158

    carbking
    Member

    Rigley - the more "tire kicking" you do before you buy, the less you have to do after you buy (including not having to rebuy because you bought wrong!).

    In migrating an O.E. carb from one basically stock application to another, FOR BEST RESULTS, the donee engine should be within +- 3 percent of the donor engine. Adding headers won't change this, but adding a larger cam with headers might.

    So ASSUMING your stock flatty is a Ford (other companies offered flat head engines) and is a 239 CID:

    3 percent of 239 is approximately 7. Thus the donor engine (for best results) should be from 232 CID to 246 CID.

    Not many WCFB's fit into that category. You just need to research what might be available, and how much you wish to spend.

    Other carbs from somewhat larger engines MAY be used, with a resultant decrease in city driveability.

    Jon.
     
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  10. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    I have a WCFB on a '58 283 that, aside from being 40 over, is bone stock. Essentially a restored engine. The tag on the carb reads 2005 that, according to my Mitchell Manual, was originally used on a 331" Cad.
    It works well but I'd like it to work better...
    Mileage is around 15-16 maximum on the highway and only about 12 in town. It's a little fat.
    I'm looking forward to learning more about tuning this carb on this thread:)
    [​IMG]
     
  11. Maybe this is not WCFB related but are the old Weber 4 barrels somewhat the same? If so. .. here is a sceneario ... and a question. ..

    I used to have a stock 455 in a 2000lb roadster with daul 600 CFM carburetors ran good and got okay mileage... when I added a snotty cam and a set of aluminum heads I actually got better performance as well as mileage.

    My question is. .. should I have run 500CFM carbs? And where is the real difference between the two carbs?

    Posted using the Full box of Crayons on the Kitchen Walls App!
     
    Last edited: Dec 17, 2013
  12. TERPU
    Joined: Jan 2, 2004
    Posts: 2,279

    TERPU
    Member

    Thank you so much for offering this. I play with WCFB's and always work hard at it. It'll be nice to have somebody set me straight.


    All the best,

    Tim
     
  13. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,695

    56sedandelivery
    Member Emeritus

    carbking, You have opened the door, or should I say the floodgates? Here's my question and concern. I have TWO of the EARLY 56 Chevrolet, dual quad intakes, for the 225 HP version of the 265. Finding the "correct" carbs is impossible, or EXTREMELY expensive! So, most guys make a pair of "clones". What about the "weight" for the secondaries; it's roughly twice the size on single 4 barrel applications as it is on the dual quad setups? What to do, if anything? I have everything to rebuild and assemble one complete setup, but the "weight" concern is holding me back. What would you advice? I also have a Weiand setup with AFB's, but I want things to look stock, as much as possible. Thanks, butch/56sedandelivery.
     
  14. carbking
    Joined: Dec 20, 2008
    Posts: 3,158

    carbking
    Member

    Butch - the "weights" should not concern you near as much as having the larger bodies. The original dual quads were WAY too large for much except racing on the 265. Larger carbs are......well, larger.

    If you really want to try this, Chicago Corvette has reproduced the weights.

    Wingnutz - sorry, no comment on the weber clones.

    Rich - take a look at the post directly above yours on done/donor engine size.

    Jon.
     
    Last edited: Dec 18, 2013
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  15. carbking
    Joined: Dec 20, 2008
    Posts: 3,158

    carbking
    Member

    The information in this particular post is meant for those with basically stock to high performance STREET applications; it may or may not apply to race only.

    Possibly a wee bit of "carburetion 101" might be useful in this thread.

    In general, there are three major components effecting the atomization of fuel: (1) air velocity which is probably the most important, (2) heat, and (3) A/F ratio.

    When too large a carburetor is installed, the air velocity in the venturii drop, resulting in a negative pressure in the fuel wells less than the carburetor was designed to see. This results in a LEAN mixture. This fact is often obscured with carburetors with vacuum operating metering (the vacuum piston/spring/metering rods used in the WCFB). The too large carburetor may have insufficient vacuum to operate the rods properly (lower vacuum will mean the rods will be pushed up too soon by the spring) thus creating a very RICH condition because the rod power tip (low vacuum segment) will be in the jet during conditions when the larger (leaner) "cruise" section of the rod should be in the jet.

    Because of the above, too large a carb may run well (with possibly less fuel economy) at cruise speeds, but have less than optimal driveability at lower RPM (city driving).

    It may be possible to somewhat compensate for this by changing to a weaker vacuum spring and/or changing the jetting; but the larger carb will never have the driveability of one that is the correct size for the air flow requirements of the engine.

    The above I often summarize by simply stating that the best tuning is done BEFORE the carburetor is purchased.

    Jon.
     
  16. carbking
    Joined: Dec 20, 2008
    Posts: 3,158

    carbking
    Member

    Adjusting the vacuum spring:

    The design of the WCFB allows for easy testing of the vacuum piston spring.

    When the engine is warmed to normal operation temperature:

    (1) Shut off the engine
    (2) Remove the air cleaner
    (3) Remove the two screws holding the small casting covering the metering rods
    (4) Place the screws and casting over on the work bench
    (5) Observe the position (height) of the metering rods.
    (6) Have a helper start the engine and run at idle
    (7) Again observe the position (height) of the metering rods. They should now be much lower, as the engine vacuum should have pulled them down into the jets.

    Shut off the engine.

    If the rods were down, replace everything, your spring is probably OK. If the rods were still up, remove the rods, THEN the airhorn, and replace the vacuum spring with one with slightly less tension. Replace the airhorn THEN the rods, and repeat the test.

    Jon.
     
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  17. This is the kind of information that might make your head explode the first time you read it. :eek: But if you stick with it and start to realize how things like pressure differentials affect the flow of air and fuel in a carburetor, you'll do a lot less hair-pulling when you're diagnosing a problem. :D


    Unless, of course, it's turns out to be an ignition problem... :mad:


    Thanks, Jon!
     
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  18. HEATHEN
    Joined: Nov 22, 2005
    Posts: 7,591

    HEATHEN
    Member
    from SIDNEY, NY

    Rich, I'm thinking that someone stuck that I.D. tag on your carb after the fact. An early Cadillac WCFB wouldn't even have the correct bolt pattern to bolt to your Chevy intake, and the choke cover isn't from a Caddy carb of that era.
     
  19. carbking
    Joined: Dec 20, 2008
    Posts: 3,158

    carbking
    Member

    Rich - my bad, I didn't look at the picture, and I agree with Heathen on both counts. Do you have a picture of the other side of the engine showing the throttle arm?

    Jon.
     
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  20. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    Here ya go....
    I should clarify a little. The engine runs very well over all. Easy to start, good idle, no stumble on acceleration, no surge at cruise.... The truck is a '36 with a C4mated to the 283 and 3:54 gear ratio and 7:00X 16 tires. I'd guess it weighs no more than 3,000 lb. the engine has about 3,000 miles on it now.
    It's not a rocket ship.... But not a complete slug either.
    I'm not hoping to gain a lot of performance but rather to make certain it's set up properly to obtain the best performance and economy the engine combination is capable of.
    [​IMG]
    I'm already pretty tickled that I might find out more about what the carb was actually off of as I always thought it unusual for a carb that old to still have the tag.
    It's the number I used to buy the carb kit
     
  21. HEATHEN
    Joined: Nov 22, 2005
    Posts: 7,591

    HEATHEN
    Member
    from SIDNEY, NY

    That's definitely a Chevrolet throttle arm.....I'd say that it's the carb that came with the intake. At the very least, with that choke style, it's from a '57 or '58.
     
  22. Rich Wright
    Joined: Jan 9, 2008
    Posts: 3,922

    Rich Wright

    Thanks!,
    That would be a real and welcomed stroke of luck as the carb came from a friend in Las Vegas who had no idea what was.
    When I got the engine it was missing the carb and generator, but other wise complete and completely unmolested.(and thoroughly worn out, of course.)

    Not that I'm a fanatical restoration guy but..having the correct carb will be a big plus as my intention all along was to restore the engine as close as possible to factory specs.
     
  23. Alex D.
    Joined: Jun 9, 2009
    Posts: 317

    Alex D.
    Member
    from Hydes, MD.

    What could be causing my dual quad’s throttle to stick open only while the engine is running?
    The carburetors are a matched pair of WCFB 2532S that have just been rebuilt. The throttle plates move freely and completely close with all the linkage hooked up to run straight. Once the engine is running and choke disengaged the throttle linkage feels like there something binding. With the engine running at 2000+ rpm and not returning to idle, when you shut it down, you can observe the throttle plates closing.
    Any ideas of what is going on within these WCFB’s to give a sticking throttle?
     
    Last edited: Apr 30, 2014
  24. powrshftr
    Joined: Mar 29, 2013
    Posts: 4,550

    powrshftr
    Member

    Alex,
    It sounds like when the engine starts to make a little torque and twist in its mounts,the throttle linkage is binding or pulling,causing the throttles to hang open.
    Do you have rod type linkage or cable style?

    Scott


    Posted using the Full Custom H.A.M.B. App!
     
  25. Alex D.
    Joined: Jun 9, 2009
    Posts: 317

    Alex D.
    Member
    from Hydes, MD.

    Scott; I have cable from the pedal to the carbs. I can disconnect the cable at the carbs and still have them sticking open while running. It has to be something in the carbs while the engine is running.
     
  26. powrshftr
    Joined: Mar 29, 2013
    Posts: 4,550

    powrshftr
    Member

    Alex,
    I've had warped baseplates in Autolite 4100 carbs cause a similar situation.
    When sitting on the bench the butterflies operated freely,but once bolted down,the warped baseplate would straighten to mate with the intake,putting the butterflies into a bind.

    I don't know the Carters well enough,but could there be something out of adjustment with the secondaries coming in really early or something?

    Let's hear from some Carter gurus on this one.Im really interested to hear some opinions on this one.

    Scott


    Posted using the Full Custom H.A.M.B. App!
     
  27. jimvette59
    Joined: Apr 28, 2008
    Posts: 888

    jimvette59
    Member

    Alex why is the engine idling at 2000 RPMs ?
     
  28. Alex D.
    Joined: Jun 9, 2009
    Posts: 317

    Alex D.
    Member
    from Hydes, MD.

    Scott; Bolted down, the primary and secondary butterflies operate freely on both carbs. When the engine is running is when there is something binding.

    Jimvette59; I guess i meant to say it won't idle down once the throttle is released. the engine races to 2-3000rpm until I kick the gas pedal, and still won't close completly. When you shut off the engine, you can observe the throttle linkage then closing.
     
  29. jimvette59
    Joined: Apr 28, 2008
    Posts: 888

    jimvette59
    Member

    Alex did you adjust the choke ?
     
  30. Alex D.
    Joined: Jun 9, 2009
    Posts: 317

    Alex D.
    Member
    from Hydes, MD.

    jimvette59; one electric choke on the rear carburetor. Choke linkage on the front carb has been removed. The engine is at operating temperature and free from the fast idle cam..
     

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