Float valve -DELLORTO Ø=5,0mm- PHBH, PHBL -

The float needle valve provides a regulated fuel supply into the carburetor. The carburetor floats it. At a certain level defined by the carburettor manufacturer, the float needle seals the inlet bore of the needle valve seat. This is ensured by the rubberized cone tip of the needle. If the float level drops, the float needle opens an annular gap and the fuel can run again. The size of this annular gap significantly influences the filling speed of the float chamber.

If the needle valve is too small, the fuel supply may no longer be sufficient under full load. If the valve is too large, the engine can literally be flooded with gasoline, resulting in increased gasoline consumption, poor running culture and other unsightly results.

Float needle valve size
One is primarily guided by the main nozzle used to determine the optimum size of the float needle valve. Approximately 30% larger than the main nozzles is the rule of thumb. An engine with a main nozzle requirement of 130 therefore requires a float needle valve in the order of ~170.

• Special cases

- Vespa
The 30% recommendation refers only to carburettors that receive falling gasoline, i.e. where the tank is higher than the carburetor, such as Lambretta.
When used on vehicles where the carburetor is at almost the same level as the fuel level in the tank, the float needle valve can also be selected up to 50% larger than the main nozzle. This is the case with all Largeframe Vespa such as the PX, Sprint, Rally and many other older models. Due to the very small difference in height between the two communicating systems, a larger than usual float needle valve helps to ensure a permanent sufficient fuel supply.

An engine with a main nozzle requirement of 130 requires a float needle valve in the order of ~200.

- petrol pump
If a fuel pump is installed, the float needle valve can be smaller than usual. The pump pressure ensures sufficient filling. In addition, a branch with return flow into the fuel line in front of the carburettor should be installed. This prevents the excess fuel from being pressed into the carburettor against the float pressure.

(machine-translated)