A big advantage of the PHB carburettors is their simple and good tunability as well as their insensitivity to weather changes. The PHBH shows quite fast and clearly if the mixture is too rich or too lean. A Mikuni or Keihin carburettor usually runs surprisingly well, even if tuned too lean, which unfortunately can also quickly lead to problems.
On most scooter engines, the following basic fuel mixture has proven to be a good starting point for the PHBH series:
If problems with the fuel supply are suspected, it is advisable to convert to a larger float needle valve (#250).
BS Carburettor = adjusting screws in suction direction left