Re: WCFB Carburetor Venturi inserts?

Posted by DavidPackard On 2021/3/3 23:27:08

Chris R

The main difference between the 985S and 2084S configurations is the diameter of the secondary ‘main venturi’. The 985S parts list uses a 1 1/16 venturi, while the 2084S uses a 15/16 item. As you would expect once you change a venturi there were also different ‘jetting’ between the two carburetors. The original venturi size is cast into the float bowl/venturi casting, and can be seen in the photo as 1 1/16. Carter manuals acknowledge the interchangeability between the 985S and 2084S carburetors

The plot thickens somewhat in the ’54 Cavalier. In that application there is a 15/16 ‘secondary main venturi’ model (2103S), and a 1 1/16 ‘secondary main venturi’ model (2124S). My ’54 Cavalier is equipped with a 2103S carburetor . . . . which would be the smaller of the two.

Seems that WCFB carburetors with a 15/16 secondary venturi is rarer than I would have guessed. Oldsmobile used them in ’53, ’54, and ’55. For each of the original carburetors there was a later model replacement, but those replacements were also configured with a 15/16 secondary venturi. I could not find another example where the replacement carburetor had a smaller secondary venturi.

The float bowl/venturi casting (known as the Main Body in Carter speak) is one of the few parts (perhaps the only) that does not appear in the illustrated parts list. Back in the day you can buy the body flange assembly and the air horn assembly, but not the casting between the two, leaving us with the possibility that the Packard dealer may not have been able to buy the parts necessary to convert a 985S to a 2084S at the dealer. I guess this assumes there was an itchy that needed scratching out in the field and whether the ’53 Cavalier was misbehaving. Given that other car manufacture’s where not ‘down-sizing’ the secondary’s I’m thinking Packard was not chasing lower fuel volatility.

Now the question is whether the casting in the photo was modified by an individual, or was it an authorized repair/overhaul procedure to convert the larger casting to the smaller specifications. I would think the step between the Main Body and the venturi inserts suggest this was not a Carter modification. I would question whether that geometry would ever act as a venturi . . . lots of turbulence shedding off of the edge, and those areas where material was removed (aligned with the struts holding the primary venturi) look like another opportunity to create turbulence.

I’ve never seen anything like your photo, or heard of venturi chokes, and I was an old hotrodder . . . just old now! I can’t imagine how much CFM that modification cost. What secondary jets and metering rods are installed?

dp