Checking The Air/Petrol System; How Good Is Your Carburettor - MINSK Repair Manual

Checking the Air/Petrol System
If there is a good spark to the sparkplug but the engine is still not starting then
the problem is with the air/petrol system. Essentially there is too much petrol, too
little petrol or water is getting into the engine and fouling the sparkplug. The
problems causing these involve the air filter, the carburettor, the petrol and the
seals between them. Of these it is the carburettor that can cause the most grief, so
you need to understand its internal mechanics first.
petrol tube,
petrol filter
air filter
under side
panel

How Good is your Carburettor?

The small float tank in the carburettor and the small blocking pin connected to
it regulate how much petrol lies dormant in the bottom of the carburettor. The
float tank can cause problems if it can't move freely, if it is adjusted wrongly or if
it is damaged. If the float tank gets stuck below its top most position – the point
when the pin cuts off the petrol coming into the carburettor – then petrol will
continuously flow into the carburettor and flood the engine because the stopping
pin will never be pushed all the way into the petrol line. If, on the other hand, the
float tank is adjusted wrongly, it will cut off the petrol prematurely, ensuring that
the bike will not run on idle. Remember that the idle jet is shorter than the
accelerator jet and will be high and dry is there is not enough petrol at the bottom
of the carburettor. You also must ensure that the float tank has no leak to it,
otherwise a little petrol will get in and mess up its buoyancy – damaged float tanks
©Digby Greenhalgh 2000
Minsk Repair Manual
air box
16
Air/petrol
System
carburettor,
rubber seal
and gasket
seals