Yamaha F4B Service Manual page 39

Medium speed operation
When running at medium speed, the air that has entered through the main bore a flows faster,
causing negative pressure to increase in the main bore a.
When the negative pressure in the main bore a increases, the fuel is sucked from the main jet a to
be mixed with the air that has entered from the main air jet b through the emulsion tube c, and
then drawn into the main nozzle b.
The fuel drawn into the main nozzle b is mixed with the air in the venturi, producing air and fuel mix-
ture that will be supplied to the engine.
The air and fuel mixture is simultaneously supplied to the engine through the pilot hole d and the
bypass holes e.
A Air
B Fuel
C Air and fuel mixture
d
e
b
a
b
c
a
Fuel system
0
1
2
3
4
5
6
A
B
C
7
8
9
10
A
2-10