Table of Contents
Advertisement
INSTRUCTION
FOR CARBURETOR
(MODEL VM
-
30)
This
manual has
been
prepared for those who
engage in maintenance and repair of
Model VM-30
carburetor
installed
to Polaris Model
EC-40,
44,
50 snowmobile
so that they may work with
proper
understanding
and
knowledge
of its
constructions
and functions.
1.
Constructions
and
functions.
Model VM-30
carburetor
has varying
constructions
depending upon varying driving
conditions, and
is
constructed
with
the float
system,
the pilot system, the main
system, and
the
starter system
(initial
starting device!.
1-1.
Float
system
(Fig.
11
The float
system
is designed to maintain a
constant
height of gasoline during
operation.
When the fuel flowing from the fuel
pump
into the float
chamber
through the needle valve reaches the
constant
fuel
level, the float
rises.
When the buoyancy of the float
and
the fuel pressure of the fuel pump balance, the needle valve
sticks fast to the needle
seat,
preventing further delivery of gasoline, thereby holding the
standard
level of
gasoline.
The standard level of gasoline is set at below 30
mlm
± 1 from the center of the main bore.
1-
2.
Starter system
-
Choke system (Fig. 2)
The starter system is designed to make the engine
start
quickly in
cold
weather. It is constructed with functional parts
such as a starter jet, a starter emulsion tube, and a starter plunger
etc.
When the engine starts with the throttle valve closed and the
starter
plunger wide open, the intake negative pressure of
the engine works on the fuel nozzle. By this negative pressure the fuel is measured by the starter jet, mixed with air in
the starter emulsion tube, absorbed into the plunger chamber, mixed again with air from the starter air inlet, made the
most suitable concentration of fuel-air mixture for initial starting, and delivered to the
engine
through the fuel nozzle.
In this starter system, you can be sure of initial starting without any skill of operation, since both fuel and air are
measured and the constant fuel-air mixture ratio is always
secured.
1-3.
Pilot system (Fig. 3
&
4)
The pilot system is designed to deliver gasoline during idling and low-speed driving.
Fuel for idling is measured by the pilot-jet, mixed with the air regulated with the air-screw, mixed again with the air
from the by-pass, and delivered to the engine through the pilot outlet. The concentration of
fuel-air
mixture for idling
is determined by the air screw. When the air
screw
is
closed
the amount of air is reduced and the fuel -air mixture is
en-
riched. When the air screw is opened the amount of air increases and the fuel -air mixture is lean.
When the throttle valve opens slightly during low-speed driving, gasoline injects through the by-pass in addition to the
fuel-air mixture from the pilot outlet to secure smooth operation of the engine. When the throttle valve opens wider,
approximately above 1/8 of the diameter of the main bore, gasoline injects through the needle jet. The adjustment of
the time and the amount of injection from the needle jet is
chiefly
performed by the cutaway furnished on the side of
the air cleaner of the throttle valve.
1-4.
Main system (Fig. 5
&
6)
The main system is designed for delivering fuel between low·speed driving and
high·speed
driving.
The fuel during the low·speed driving is delivered, as
shown
in
fig.
4, from the pilot
system and
the main
system.
Dur-
ing intermediate-speed driving (the opening
of
the throttle valve is
above
1/4),
the fuel is largely delivered from the main
system. The fuel during intermediate-speed driving flows into the needle jet
through
the main jet
and mixes
with
the
air measured by the air-jet to make a fine
spray
of fuel-air mixture
of good quality.
19
•
Advertisement
Table of Contents
