Radne Motor Raket 95, Owner'S Manual

www.raketengines.com

www.raketengines.com

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 Raket 95 Manual - English

Raket 95 Manual - English     

23        

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.