MINSK Repair Manual page 20

are very hard to replace. You also want the stopping pin to be able to move up and
down freely. Sometimes it can get jammed.
Of critical importance if you have the square
carburettor is the tiny plastic washer on the stopping
pin. If it is genuine then this washer will be clear,
uniform and well made. This washer ensures that when
the float tank moves up with the level of the petrol to
its top position – i.e. when the carburettor is full of
petrol – the pin performs its job correctly by stopping
any more petrol getting in. Conversely, should the
washer get dirty, then the stopping pin can get stuck
and block any further fuel from entering the carburettor.
The washer can not be replaced without buying a new
carburettor. The round carburettor does not have this
washer, using instead a ball bearing to stop the petrol
from flowing into the carburettor.
Another problem concerns the jets in the carburettor,
which if old and worn, won't spray the petrol and air in
the right way. When you turn the accelerator handle, a
long pin moves up and down through a hole at the end
of the accelerator jet through which the spray comes out
of. This action, over time, wears the pin and the hole
down, thereby allowing more petrol into the petrol/air
spray. Mechanics correct this by placing a thin piece of
wire through the hole in the jet to limit the amount of
petrol which can get through. This works pretty well but is haphazard because if
the wire breaks or becomes loose then the carburettor won't work. No problem if
you are experienced and have some replacement wire but quite nasty otherwise.
The last items of importance are the gasket seals both inside the carburettor as
well as between the carburettor and the engine and the air-box. The two seals used
in the rectangular carburettor need to be sound and not cut up or worn through.
The same goes for the round carburettor, but it only has one seal between the main
middle section and the bottom cup. The same can be said for the two larger gasket
seals on either side of the hollow square shaped component which is fitted
between the carburettor and the engine. These two seals should also be sound.
Always make sure the square shaped component and the carburettor are fitted
snugly between the gaskets when you screw the carburettor back on.
Likewise, if the rubber seal between the carburettor and air box is improperly
fitted or the seal is not sound then too much air and dirt will spoil the combustion.
If water gets into the carburettor then it will sink to the bottom of the
carburettor. When enough water collects there then it will get sucked up the jets
and foul the combustion in the cylinder. Sometimes it only gets sucked up the
longer accelerator jet and fouls the bike when you rev it up. So keep your air-box
clear of water and check your petrol filter regularly for water build up.
©Digby Greenhalgh 2000
Minsk Repair Manual
17
petrol
enters
here
washer
stopping
pin
As the float tank
rises it pushes the
stopping pin into
the petrol tube