Robin America EH63, Service Manual

Page: 57 / 85

– 54 –
FLOAT SYSTEM
The float system is consists of a float and a needle valve, and maintains a constant fuel level during
engine operation.
The fuel flows from the fuel tank into the float chamber through needle valve.
When the fuel rises to a specific level, the float rises, and when its buoyancy and fuel pressure are
balanced, the needle valve closes to shut off the fuel, thereby keeping the fuel at the predetermined level.
Air vent hole of float chamber is provided around the carburetor air hone and the fuel vapor is sucked into
the combustion chamber. This closed system has unti-dust feature.
PILOT SYSTEM
The pilot system feeds the fuel to the engine during idling and low-speed operation.
The fuel is fed through the main jet to the pilot jet, where it is metered, and mixed with the air metered by
the pilot air jet.
The fuel-air mixture is fed to the engine through the pilot outlet and the by-pass.
At idling speed, the fuel is mainly fed from the pilot outlet.
MAIN SYSTEM
The main system feeds the fuel to the engine at medium-and high-speed operation.
The fuel is metered by the main jet and fed to the main nozzle. The air metered by the main air jet is
mixed with the fuel through the emulsion tube, and the mixture is atomized out of the main bore. It is
mixed again with the air taken through the air cleaner into an optimum fuel-air mixture, which is supplied to
the engine.
CHOKE
The choke is used for easy start when engine is cold.
When the starter is operated with a choke valve fully closed, the negative pressure applied to the main
nozzle increases and draws much fuel accordingly; thus easily start up the engine.
ACCELERATOR-PUMP SYSTEM (EH72 only)
When the throttle is opened rapidly for acceleration, air flow and manifold vacuum change almost
instantaneously. Because fuel is heavy and lags behind air flow, a momentary leanness results. The
accelerator-pump supplies extra fuel for smooth operation during this condition.
At constant load condition, a vacuum passage in the carburetor applies manifold vacuum to the pump
diaphragm and the pump diaphragm is held to pull position.
When the throttle is opened rapidly for acceleration, the manifold vacuum is dropped, the pump diaphragm
moves by the diaphragm spring, the fuel in the pump chamber push out by the pump diaphragm and the
fuel gush out from the accelerator-pump nozzle.
FUEL CUT VALVE
Fuel cut valve, operated with starter key switch, is equipped with main system of carburetor for preventing
engine running on and after burning.
When the key switch is on, the valve is activated and the plunger is pulled in to open the main jet.
When the key switch is off, the power source to the valve is off. The plunger is pushed out by the return
spring and stop the fuel flow of main jet.