Re: Carter carb assistance

Posted by DavidPackard On 2024/4/4 18:25:58

Dhart1977
A Carter 502S is a carburetor intended for a Hudson, with 1.187 main venturi diameter, and 1.25 throttle plate diameter. The 502 does have anti-percolation valves, but no starter switch or distributor vacuum port.

A Carter 644S is a carburetor intended for a Packard, with 1.125 (smaller) main venturi diameter, and 1.25 (equal) throttle plate diameter. The 644 does have anti-percolation valves, and both a starter switch and distributor vacuum port.

The diameter of the primary venturi is the same for both carburetors (11/32 inch). The external linkage differs between the two items.

Implication: Based on the larger main venturi size the Hudson carburetor would likely have a higher CFM rating. The distributor vacuum could be connected directly to the intake manifold, while an auxiliary starter switch would suffice. External linkage may (emphasis on vague) be swapped. The entire throttle shaft would need to be swapped, and that’s an overhaul step that I for one avoid. New linkage from the firewall to the carburetor would likely solve the incompatibility.

With the difference in the main venturi size avoid a comparison between the jet/rod sizes. At any given airflow a larger main venturi will result in less airflow through the primary venturi, and thus less suction on the discharge nozzle. To achieve the same fuel flow with less suction the main jet / metering rod flow area must increase. The Hudson 502 main jet is 0.086 inch diameter, with a power step rod diameter of 0.044 inch. The Packard 644 main jet is 0.0846 inch diameter, with a power step rod diameter of 0.045 inch. Resulting in a Hudson fuel flow area 0.00858 in**2, and a Packard fuel flow area 0.00806 in**2 (both on the power step). The difference in fuel flow area is to accommodate (likely at constant air/fuel ratio) the main venturi size change . . . a 502 equipped engine will not likely run any ‘richer’ or ‘leaner’ than the same engine with a 644 installed.

dp