Carburetor Inner Passages; Idling Passage - TOHATSU MFS 4 Service Manual

Fuel System

3. Carburetor Inner Passages

1) Idling Passage

a - Air intake
b - Air vent inlet
c - Main air jet
d - Pilot air jet
e - Bypass port
f - Pilot outlet
g - Throttle valve
h - Fuel inlet
i - Main jet
j - Pilot jet
k - Choke valve
l - Main nozzle
m - Air bleed
å Air
∫ Air-fuel mixture
As engine rotates, intake valve opens and piston moves from top dead center toward bottom dead center, the piston
movement causes vacuum or low pressure area to occur in the back of throttle valve.
Then, the air enters carburetor through air intake port, runs through throat venturi and throttle valve, and then is sucked into
the combustion chamber area in the cylinder that is in air intake stroke.
The float chamber receives atmospheric pressure through air vent. This pressure causes fuel to be sucked into low
pressure area in the back of throttle valve. The fuel is sent to main fuel well through main jet, runs through idle passage and
pilot jet bypass (off idle) port, and then is ejected from pilot outlet. When this fuel goes through bypass port, it is mixed with air
in the carburetor bore to be air-fuel mixture which is sucked into the cylinder.
4-8
a
d
c
k
å
e
j
b
l l
l m
h h
i
<Over view>
g
f
<Side view>
∫
4st 4/5/6 2011