Aeon AT56-69E, Service Manual, Page: 121 / 196

FUEL AND CARBURETOR
6-11
IDLE AND LOW SPEED CIRCUIT
At idle with the throttle plate closed and the air stream cut off,
idle speed is maintained by fuel metered through the slow jet.
Air from the slow air jet mixes with the fuel and is delivered to
the port at the vacuum side of the throttle plate. At low speed
as the throttle plate is cranked open the transfer ports are
exposed to the vacuum side of the throttle plate and additional
fuel is directed to barrel of the carburetor.
With the throttle plate cranked open a quantity of fuel also
enters the air stream from the needle jet. The idle and transfer
ports supply additional fuel to the carburetor barrel to assist
during the transition period from idle to mid range.
The venture opening is reduced by the low position of the
vacuum piston. This enables initial air stream velocities
provide great quantities of fuel necessary or good acceleration.
MIDRANGE SLIDE POSITION AND FUEL
DISCHARGE
As the throttle plate is opening, airflow increases through the
carburetor and the pressure drop in the venture near the needle
jet increases.
The low pressure in the venture travels through the vacuum
port in the vacuum piston to the chamber above the diaphragm.
The chamber beneath the diaphragm is vented to atmospheric
pressure by a passage from the chamber to the carburetor inlet.
The higher pressure at the underside of diaphragm overcomes
spring pressure and moves the vacuum piston upward in
proportion to the pressure difference between chambers.
The tapered needle moves upward with the vacuum piston
opening the needle jet. The higher pressure in the float
chamber force fuel into the needle jet passage. Air at
atmospheric pressure from the main air jet is forced through
the main bleed tube openings and mixes with the fuel. The
fuel/air mixture is than delivered through the needle jet into air
stream.