Carter specified the spring loaded needle and seat for most of the YF carburetors used as aftermarket on Chevrolet.

When adjusting the float level with a Carter spring-loaded needle and seat, ALWAYS set the specified dimension with the float resting on the valve with its own weight only. DO NOT COMPRESS THE SPRING. Compressing the spring will give a false setting.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop