(57) The invention provides a carburettor for an internal combustion engine, comprising
an upper plate element, a lower plate element and a side wall structure which spaces
the plate elements from one another to define a mixing chamber within its surround.
A tangential inlet to the chamber is defined in the side wall structure while a central
outlet from the chamber is provided so that fluid entering the inlet follows a vortical
path en route to the outlet. In a preferred arrangement the inlet is provided with
a variable throat which includes a hinged flap adapted automatically to open the throat
in proportion to air flow therethrough so that velocity through the throat remains
substantially constant until the flap is fully open. A fuel jet is disposed a short
distance downstream from the free end of the flap so that with the flap partially
open, the jet is subjected to a constant pressure differential and in order to compensate
for increasing airflow, a number of jets are provided successively upstream from the
first jet. Once the flap is fully open, increased air flow results in an increased
pressure differential over the jets so that the air fuel ratio remains substantially
constant. A feature of the invention is that during low engine speeds, for example,
during starting and idling, the air velocity is sufficiently high to effect vaporisation
of liquid fuel. While the carburettor is of extremely simple construction, the mixing
chamber ensures a high degree of vaporisation of liquid fuel without the application
of heat or dependancy upon a manifold for the internal combustion engine.
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