Onan MJA Series Service Manual page 36

J4 J!'U.I:!.;L SYSTEM
4. Adjust the choke, Sect
3.2.4.1.
5. Attach the electrical connec­
tion, and reinstall the air
silencer adapter and air
housing.
3.2.5 CARBURETOR GASOLIl\TE
The gasoline carburetor is a hor ­
izontal draft type, -with an up ­
turned intake horn (air silencer
adapter). The carburetor con ­
sists of 3 major sections - the
bowl
and float, the idle circuit,
and the load circuit.
~
\ \ t\".
~',
....-FUEL INLET
\
~~
... ; jeLVEjSEAT
FLOAT
\~l~r~.I~=~l
CA.R. BURETOR
PI N
~~~:~
,
/'dt-Q.
.1" BODY
i,. . . . . . . .
FUELINLET
I \
VALvE
~
L=J
CARBURETOR
FLOAT
FIG 3.2.G-INLETVALVE
.,\
Fuel enters the. carburetor through the inlet valve, Fig 3.2.
G,
and pas ­
ses into the float chamber. To control the fuel level in thEE bowl, the
float, closes the inlet valve when fuel reaches a certain height, and opens
it when the fuel level drops,.
The idle circuit, Fig 3.2. H, supplies fuel during no load operation and
for small loads. Since the throttle plate is nearly closed at no load,
the intake manifold vacuum is high <tnd the pressure difference between
the manifold and float chamber causes fuel to flow through the idle cir ­
cuit. The pressure difference draws fuel up through the hollow center
of the main adjusting needle, through passages in the carburetor body
to the idle port. Bleed holes in the main. adjusting needle allow air to
bleed in and mix with the fuel. When the throttle is almost completely
closed, the fuel passes out throu,gh the idle port, controlled.by the idle
~
MAIN JE:T OPE:RATING
FIG 3.2. H - CARBURETOR IDLE FIG 3.. 2.1 - CARBURE TOR LOAD
CIRCUIT CIRCUIT