High Speed Passage - TOHATSU MFS 4 Service Manual

Fuel System

3) High Speed 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 throttle valve is turned to a position over bypass port, the low pressure produced in the back of throttle valve extends to
an area near main nozzle. At the same time, as flow of air that runs through carburetor bore increase, the whole space in
the venturi becomes low pressure. The low pressure in this venturi causes large suction force in the main nozzle. The fuel
goes through main jet, flows into main fuel well, goes through main nozzle, and ejects from venturi.
The fuel that runs through main nozzle is mixed with air that comes from air bleed hole made on the side of main nozzle to
make the fuel/air (atomized). When throttle valve is fully open, the amount of fuel is determined by the size of main jet.
The idle and off-idle passages keep feeding fuel as well as air to the engine.
4-10
a
d
c
k
å
e e
j
b
l l
l m
h h
i
<Over view>
g
f
<Side view>
∫
4st 4/5/6 2011