'54 Carter BBS Issue

[denmopar]

Hi guys- Been a while.

 

 My '54 Plymouth had suffered under the "golden hammer" before I got it. The idle stop screw boss was broken off the bowl casting along with other bent and missing parts, necessitating a replacement.

Since my '54 Belvedere has the earlier 217 engine with integral "Climatic" choke, the Carter BBS model was the 920S. Not many (three speed manual) Plymouths were equipped with that model since the mid-year change to the 230 c.i. engine. The OEM carb is "made of unobtainum" in these parts..

So, I found a new-in-box model 2604S. which is a universal replacement carb for 1957 flathead engines. I mixed parts to create a "Frankencarb" due to the original throttle plate and bore being 1/8" smaller diameter than the new carb's throttle plate dimension.

 

 It works quite well except for a  mid-throttle, no-load erratic miss/ stuttering when warmed up. (Opened choke.) Almost behaves like erratic ignition issue, but a slight fuel enrichment clears this right up. All other modes/ phases of operation are  as they should be.

I used the adjustments / settings specs for the OEM 920S carb.

Along with  the original throttle plate, I decided to use the replacement main jet......The reason for using the newer main jet was that even though it is larger for the bigger engine with higher compression ratio, it still measured smaller than the well-worn main jet I pulled from the original carb. (This according to Carter specs for both models.)

 

I've a couple of questions:

There is a two-piece stainless steel diffuser in the intake just below the carb mounting boss. As found, it was placed in the manifold on a 45 degree angle to fuel path. I'm not too sure this is correct. No info in that universal 1946-54 shop book.....

I placed it with the two tines in the path to the two center cylinders with no change to the operation of the engine. Can someone tell me for certain the proper orientation of this diffuser?

 

Should I also be looking at the calibration of the "Step-up" piston / circuit for the no-load erratic miss?

 

Any insights appreciated.

 

Dennis

Edited November 12, 2013 by denmopar

[pflaming]

Your reference to a Carter Ball & Ball carb # BBS 920 S caused me to take a look at the numbers on the carb I picked with the overdrive. It has  an automatic choke, different from the carb on my B3B.

 

Numbers: On the throat 6-595; on the 'flag' D6H2, mfg by Carter Saint Louis; on the 'pot', Ball&Ball, mfg by Chrysler, Detroit, MI.

 

Question: Is this an integral " climate " choke? It is an automatic choke when is connected to a solenoid mounted on the intake manifold. and is it a 'better' choke or just another production run numbers?

[greg g]

If a slight enrichment solves the problem then it sounds like a air leak on the vacuum side of the carb.  I would check all mating areas carb to manifold, manifold to block and see if you have a leak which is leaning your mix. 

[denmopar]

The later Carter BB series used the "Sisson" external electric choke.

The early BBS series (beginning in 1954???) used the internal choke mechanism. 

The later-- (maybe 1960 with the advent of the "slant 6"???)--  BBS series went back to an external choke but with an integral unloading system.

 

 It is a bit difficult to determine the exact model carb without the data tag that, unfortunately, is often found missing from the air horn attaching screw.

One hint can be the linkage that exists on the carb. (OD or Powerflite linkage) Another is careful measurement of the main jet I.D.

 

Good thought re: carb/ manifold leaks, but I've done that....Also verified with propane and aerosol external enrichment.

Edited November 12, 2013 by denmopar