Bob - the valve pictured is the currently available spring-loaded valve for marine AFB and AVS 4-barrels. It has an orifice of 0.092, which is large for the Chevrolet YF. If this one is too large and the one you used is larger, then..........................
History:
Carter developed the spring-loaded fuel valve in the 1930's for off-road and marine application. The spring tends to make life easier on the float under extreme conditions (bow of the boat hitting waves, or a truck tire hitting large holes, being on the side of a hill, etc.). If your truck is used primarily on road, then the spring-loaded valve does not enjoy a large advantage over the solid valve (on second thought, the pot-holes in the streets around here might be an advertisement for the spring-loaded valve
)
I saw a tourist sitting in his lawn chair on the side of one of our city streets after a rain fishing in one of the pot-holes!
Seriously, the orifice size for non marine or off-road is more important than the spring.
The float in the carburetor has a certain buoyancy, and because of this buoyancy, the float will exert a certain pressure to withstand the input fuel pressure. The larger the fuel valve orifice, the less inlet pressure can be held with the same float.
As to the Chinese carburetor and your YF exhibiting the same issues? Honestly, there is insufficient data available on the Chinese carburetor to confirm or deny that assertion. Maybe yes, maybe no.
Jon
