Don - a lot of the early YF carbs did use the ball with a weight on top. I dislike using the word "all", but as far as I am aware, all of these used in YF's were superceded by the pointed needle (fewer parts to lose). Carter again occasionally use the check ball without the weight (less mass) on some of the AFB 4-barrel carbs. The mass of the discharge check valve is a "tuning aid" to time the initial discharge of the accelerator pump shot.
The white powder is zinc oxide. Carter used a sulpher-based gasket, and the sulpher in presence of humidity caused the formation of zinc oxide.
Jon.
