CONSTRUCTION DATA
The HU series carburetor is die-cast aluminium, consisting of three basic parts: metering body, pump cover plate
and main diaphragm cover plate. This carburetor incorporates many of the components found in float type
carburetors: throttle, idle and high speed mixture screws, idle speed screw and inlet needle.
High speed and idle mixture screws are spring friction type and require no packing. These mixture screws are
located on the right side looking toward air horn.
A rubber tipped needle seats directly on a machined orifice in the body casting. An inlet tension spring exerts a
pre-determined force on the inlet control lever, which holds the needle on its seat.
A metering diaphragm is subjected to engine suction on the metering chamber side and atmospheric pressure on
the vented side. Atmospheric pressure on the vented side pushes the diaphragm toward the inlet control lever,
opening the inlet needle to allow fuel to enter the metering chamber, from which it is then delivered into the mixing
passages.
The inlet control lever hooks on the inlet needle on some models and a self-tapping screw holds the fulcrum pin in
place.
Movement of the pump diaphragm is caused by pulsations from the engine, acting on it through an impulse
channel. This movement draws fuel into the fuel chamber and a reverse movement forces fuel out of the fuel
chamber through the inlet needle into the metering chamber.
An easily accessible fine mesh-filtering screen is located under the fuel pump cover and diaphragm.
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