Radne Motor Raket 95, Руководство пользователя

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Raket 95 Manual - English Raket 95 Manual - English
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which you can check by using the same
method as we have previously described.
If you still – despite everything – are not
able to receive fuel then the needle valve
must be stuck and in that case there is
nothing else to do than to continue. The
pump pushes the fuel forward towards the
needle valve, but it cannot open it through
its own force. The needle valve is held
closed by a spring that operates over a le-
ver. The master diaphragm works against
the lever, which we know from the small
rivet in the middle of the diaphragm. One
side of the diaphragm is in contact with
the carburettor’s venturi. When the fuel is
sucked out through the needle valves, the
amount of fuel beneath the diaphragm is
reduced. This in turn applies pressure to
the lever and cancels the spring’s force.
Now the inlet valve can open and more
and more fuel can flow in – the chamber
beneath the diaphragm fills up and the
diaphragm moves outwards. In this way
the spring closes the needle valve and
maintains a relatively constant amount of
fuel in readiness for the needle valves.
Fuel can find its way out of the chamber
to the carburettor’s venturi via the H and
L screws. The channels there are so thin
that the fuel will not normally escape
of its own accord but rather must be
sucked out. The shape and placement
of the channels in the venturi decide the
characteristics of the carburettor. That is
however not something that we shall go
into in any more detail here.
Now we can start with the needle valve.
Take away the pressed metal cap and the
master diaphragm together with its gas-
ket. By loosening the small screw that can
now be reached, the needle valve can be
disassembled. Be careful that the spring
does not come loose! Now you should
check the needle valve itself (nr: 25) to
ensure that its pin is totally even – change
it if you are unsure. Check that the seat-
ing at the bottom of the valve appears to
be even and undamaged. Unfortunately
it can happen that the seating sustains
damage in which case the valve will not
be able to close properly.
When you have checked and cleaned
everything it is time to reassemble the
needle valve with its lever. The spring
should not be deformed (you should
always have a couple available to change
when necessary) and the lever should
not be bent. When you assemble the
valve, the part of the lever that has a
fork that fits onto the master diaphragm’s
rivet should lie exactly at the edge of the
carburettor’s rough surface.
Now you should attach a small air pump
with a manometer (art nr: 5054) to the
fuel nipple on the pump side. Drop a few
drops of fuel down onto the needle valve
and pump up the pressure on your pump.
At approx. 1.0 kp/cm2 the inlet valve
should open and after that it should re-
lease air through it down to a pressure of
approx. 0.5 kp/cm2. Now the valve should
be totally sealed! If this test does not
appear to have worked properly then the
question is, what should we do next? The
most common problem is probably that
the valve is not sealed, and in that case
one must search for dirt or pores or else
change the needle valve. PLEASE NOTE!
Leaking gaskets on the pump side will ex-
hibit the same symptoms. If the opening
or sealing pressure is not correct then you
will have to change the spring and lever
until it does appear to be correct.
OK – now the valve is correctly adjusted.
What other faults could exist? The master
diaphragm – maybe?! It is most likely so
that far too many master diaphragms are
changed for no good reason. There are
strong forces at work on the diaphragm.
One should really be able to feel that it
has become stiff before it is definitely time
to change it. Check the gasket (that is
lying closest to the carburettor casing on
this side of the carburettor).
Assuming that you have cleaned the car-
burettor properly and that the High Speed
and Low Speed screws are not damaged,
then there is really not too much more
that can be wrong.
The only thing that remains now is to
check if the engine is difficult to start and
if it refuses to react when the setting of
the L-needle is changed. In that case
there could be dirt under the expansion
cap that is located beneath the master
diaphragm. The fuel from the Low Speed
needle passes through a small chamber
on its way out to the venturi and on very
rare occasions this chamber can become
clogged. In such a case one should bore
a 2 mm hole in the middle of the cap (nr
20) and then pry it away using a sharp
object that one can stick into the hole.
Thereafter you should carefully check
all of the channels running to and from
the chamber and seal those with a new
expansion cap that you must carefully
put in place using a mandrel 8 mm. Now
there should not be any more faults with
your carburettor.
Normally these diaphragm carburettors
are extremely reliable. They are devel-
oped for use with chainsaws and snow-
mobiles. On very rare occasions one may
come across a carburettor that does not
provide satisfactory performance. In that
case you should borrow an identical one
if possible. If you notice a large difference
in the performance of the carburettor you
have borrowed compared with your own
then you should change your carburettor.
It is more or less a practical impossibility
to alter the fuel channels in a carburettor
on one’s own.
4. Starter equipment
On engines that are equipped with a
manual coil starter (or Magnapull starter),
the coil or the return spring may need to
be changed. The basic rule regarding an
eventual change is that the return spring
may never be drawn to such an extent
that it causes a stoppage for the coil when
it is fully drawn. A small amount of “give”
should always exist in the spring when the
coil is fully drawn.