I won't discuss the Chinese carb, there really is no reason to do so, and insufficient information to do so even if there was a reason. But there is sufficient documentation and parts existing that your YF CAN be fixed.
Do you remember if the fuel valve was spring loaded or solid?
And most would never think to measure the fuel valve seat orifice, but I would suggest this is your next step.
The spring loaded valve has a hole drilled in the end of the valve opposite the point. A small spring is inserted in the hole, and a small metal pin resembling a golf tee is then inserted into the center of the spring.
Jon
