Carburetor Inner Passages 1) Idling Passage - TOHATSU MFS 9.9 Owner's Manual

Fuel System
3.Carburetor Inner Passages
1) Idling Passage
a
m
l
a - Air intake
b - Air vent inlet
c - Air-bleed inlet
d - Slow air jet
e - Bypass port
f - Idle Port
g - Throttle valve
As engine rotates, intake valve opens and piston moves from top dead center toward bottom dead center, the piston movement
causes vacuous 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
vacuous 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 vacuous area in
the back of throttle valve. The fuel is sent to main fuel well through main jet, runs through idle passage, slow jet, bypass (off idle)
port, and then is ejected from idle port. 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.
4-6
c
b
d
k
h - Fuel inlet
i - Chamber drain
j - Main jet
k - Slow jet
l - Outlet check valve - Accelerator pump circuit
m - Choke valve
e
f
g
h
j
i
4st 9.9/15/20 2008