8
User Manual
9
The carburettor
The Raket 120 is equipped with a Walbro diaphragm
carburettor of type VG6 with fixed High Speed jet.
How it works
The carburettor is connected to the fuel tank with a flexible
hose, made of rubber or plastic. The hose connects to the
fuel inlet nipple (part No 32029 - see figure).
When you pull the starter rope and the piston moves up and
down the cylinder, the pressure variations in the crankcase makes the
pump diaphragm (part No 32045) move up and down. As the outer side of
the diaphragm is connected to the fuel inlet nipple via two rubber valves, the
movement of the diaphragm will cause a pumping action that will draw fuel
from the tank to the carburettor.
NOTE! The tank and the engine shall be placed so that the carburettor
normally shall suck fuel from the tank, i.e. the fuel shall not flow freely from
the tank to the carburettor causing an over-pressure. Neither shall the tank
be placed so low that the pump of the carburettor has difficulties in pumping
the fuel from the tank.
NOTE! During normal operation the carburettor shall pump air free fuel
from the tank. If, due to heavy vibrations or excessive movements of the
fuel tank, you can observe that the fuel is mixed with bubbles of air (use a
transparent plastic hose), this may cause the engine to loose power or to
stop. If this problem cannot be solved by changing the mounting of the fuel
tank, you may try to equip the fuel take off in the tank with a fuel pick up.
Fuel pick ups are normally used in power chain saws, and may be obtained
from most chain saw service stations.
After the fuel has passed the pump it reaches the inlet valve (sometimes
referred to as the inlet needle valve - part No 32025). The normal position
for the valve is closed. The valve can be opened only if the main diaphragm
(part No 32017) is pressing down the lever (part No 32024). It is the amount
of fuel in the main chamber that makes the main diaphragm move. When
the valve is open, the fuel will flow into the main fuel chamber of the car
-
burettor. From the main chamber the fuel can flow into the venturi of the
carburettor through two jets. One jet is fixed, and controls the flow of fuel
at high speed. The size of this jet is factory set and shall not be changed. If
you change the fixed jet to another size you will either loose some power or
your engine will run too lean and seize up.
The second jet is adjustable, it is a needle valve. It controls the flow of fuel
at low speed. The normal setting of this needle valve is one turn open from
its closed position. Before you make any attempts to start the engine, make
sure that the needle valve is in the ”one turn open” position. Later you may
open it a little further to make your engine run a little richer, or close it to
make the engine run leaner.
NOTE, never set the low speed valve less than ¾ of a turn open, as leaner
settings may cause severe engine problems.
The carburettor is equipped with a cold start device, sometimes referred to
