for Yamaha RD400 C/D with original Mikuni carburetor
Keyster = KYV-03025
OEM = 23L-14107-25-00
please check and adjust float valve level if you chang float valve.
level data you find by Keyster carburetor parts in this shop, search your model.
please clean your petrol system
change complete set, not only new valve in old holder.