Thanks for the offer but I’m going to decline.  With no plans to run the car in the Big Bend Open Road Race any time soon, I’ll live with the 500 cfm carb for awhile.  It drives around good as it is and unless I really twist the engine rpms up, the lack of cfm is not noticeable.
 
In your case, the 600 cfm carb should be a good choice as it’s difficult to be oversized assuming the vacuum secondaries are working correctly and you are running any kind of upgrades such as camshaft and larger valve heads.  You might consider a stiffer spring in the secondary side to slow down the secondary opening.  The factory installed silver spring does seem to be the best choice in most instances but your combination might want the secondaries to open a bit slower.  If the car is sluggish in normal driving, then I would consider looking at the basic tuneup as you may have something going on that’s not carburetor related.

Lorena, Texas (South of Waco)

I got a 600 Summit I'd trade for your 500 Ted. It's a little too big for my set up.

Durham Missouri

Scott: If you are presumably using a ECZ-B manifold & still dealing with the carb situation, before you spend more money on it..take the carb off & make sure you have a proper seal to the intake. Due to the raised design of the intake flange, larger 4 Bbl carb gaskets such as a #55 will barely seal if at all, causing a vacuum leak..   


Paul

The Holley list #1848 4V carburetor is the recommended replacement for the 1957 Thunderbirds originally equipped with the Holley List #1273 carbs.  As such, the throttle linkage on the #1848 carb matches the original Holley.  Always keep in mind that the four barrel carburetors of the era were undersized on the various Ford applications.  Case in point are the 1957 E code engines which simply had two teapot carbs in lieu of the 400-410 cfm Ford, Carter, or Holley 4V carbs that were available on the single four barrel equipped 312’s.  With the 1957 312 single four and dual quad engines being the same other than the induction setup, the advertised HP rating was 25 HP higher with dual quads. Recent dyno testing has confirmed this to be the case and not just some marketing hype.
  
The old calculations for carb sizing work fine for stock engines that have little or no port work, small valves, and stock low lift camshafts.  Anytime the engine has been modified to improve the air flow in and out of it, then the carburetion should be examined to see if it will benefit by having it larger than what the old calculations suggest.  I’m currently running the Summit model 4010 500 cfm on my 272 which is basically stock other than having the Isky E4 camshaft and that carb is definitely undersized once the rpms are twisted up.  It’s a good driver though but if doing it again, I would opt for the Summit 600 or 750 sized carb on that same engine.  Keep in mind that vacuum secondary carbs are running on the primary side most of the time and if that primary side is sized smaller than a suitable two barrel carb for the same application, the carb is marginally on the small side.  I’ve installed a number of 750 cfm vacuum secondary carbs on hopped up Y engines and that is the carburetor of choice for both driving around and standing on the throttle.
 
Here’s the link to the article of a 303” Y build with unported heads and utilizing the Summit 750 cfm 4V  carb.
http://www.eatonbalancing.com/2015/05/01/unported-iron-heads-can-still-make-over-a-hp-to-the-cubic-inch/

Lorena, Texas (South of Waco)

I bought a new Holley 1848-1 465 CFM and couldn't be happier with it.   My motor is a .040 over 292 with 1957 G heads, iron intake and distributor.  I have no flat spots and it idles smooth as glass.  The secondaries open when they are supposed to.  Installed it right out of the box with no mods.  You'll love it.

Very good, solid advice and I thank you for it. I will follow your recommendations and get the car into my tech guy and have him narrow the problem down before I go out and spend a lot of bucks on something that really isn't a problem (like I have done before). I appreciate your taking time to help me!

Scott

Scott

Redding, California

Scott.  Don't be surprised if the technician who works on your car indicates that he needs to do a full check-up of your engine other calibrations or operating condition before putting your carburetor under scrutiny.

While your engine's operating problem may be related to the carburetor you're running, there are many other 'things' that may instead be the root OR otherwise contribute to the problem.  Generally, the carburetor is the last 'thing' to adjust after virtually everything else has been verified as being properly calibrated or operating. Ruling these other potential contributors out first, is the usual order before suspecting the carburetor or setting out to 'fix it'.

Your technician may begin with an engine vacuum gauge test done at normal engine operating temperature.  Depending upon what that testing shows, the tech. may desire to do a compression leak-down test.  He may also do an ignition system operating test with an oscilloscope.  This may lead to work related to spark plug and / or spark plug wire replacement.  After checking the ignition point dwell setting and the existing ignition timing setting, he may, IF equipped to do so, pull your ignition distributor to check the centrifugal advance curve and to assure proper vacuum advance operation on a distributor machine.  The checking of the distributor advance curves can be accomplished with the distributor installed on the vehicle's engine, but a distributor machine is preferred if he still has one.  If previously removed, after reinstalling the distributor, he may check the engine valve lash setting.  Subsequently, he'll check your ignition timing setting at idle (with the vacuum line to the distributor disconnected and taped closed) and then will check the idle adjustment of the carburetor.  After doing all of this other 'stuff', he may have you take him for a road test involving low speed operation, stop-and-go operation, engine operation in going up a long hill, acceleration to attain highway driving speed, performance when doing the equivalent of a vehicle pass at highway speed, and performance at consistent highway speed for a reasonable distance.

Your technician may do some other things, but the above narrative will give you an idea of what was common to do with pre-computer controlled engines that had carburetors, solid lifters, and ignition distributors with ignition points.    

Hope this helps! 


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Pick up a copy of HP books Holley Carburetors, Intake Manifolds, & FI and or Haynes Holley Carburetor Handbook, I have both great info on setting up carbs especially idle, off idle & cruise which sounds like your carb. I've never seen a bad carb but have seen a lot of miss-tuned carbs by folks who don't know how a carb works! I've spent my time in that line! All carbs are an amazing engineering feat, they aren't simple and everything does something to contribute to drivability, power, and economy. The trick is get it all working together!! If you don't understand the details you never will.

Auto ?   Sounds like you just have a crap carb , Y's are pretty forgiving, Ive tried a 600 Holley , 450 Holley and a 1406 600 Eddie [on there now] and Vac secondaries, lots of adjustments made and I have to say there's not much between any of them ...



"Came too close to dying to stop living now!"

Thanks for the reply! I have located such a person near me and will consult with him before I make any rash decisions-good advice.

Scott




Scott

Redding, California