Patent ID: 7407153
Filing Date: 2008-08-05
Classification: F02B,F02D,F02M,Y10S

Abstract:
1. A carburettor for a two stroke engine including a flow duct comprising rich and lean flow passages in parallel separated by a substantially planar partition, at least one fuel jet communicating with the rich passage, the partition including an aperture towards which the fuel jet is directed, and a substantially planar butterfly valve being received in the aperture so as to be pivotable between a first position, in which the flow duct is substantially closed and the aperture is substantially open, and a second position, in which the flow duct is substantially open and the aperture is substantially closed, the upstream half of the aperture being defined by an upstream semi-annular seating ledge affording an upstream seating surface which is engaged by one of the surfaces of the butterfly valve when it is in the second position and a first end surface which extends between the upstream seating surface and that surface of the partition which is directed towards the lean passage, the downstream half of the aperture being defined by a downstream semi-annular seating ledge affording a downstream seating surface which is engaged by the other surface of the butterfly valve when it is in the second position and a second end surface, which extends between the downstream seating surface and that surface of the partition which is directed towards the rich passage, characterised in that at least one of the upstream semi-annular seating ledge, the downstream semi-annular seating ledge and the valve are so shaped that, in use, a pressure differential is created between the rich and lean passages at the upstream and/or downstream edges of the valve, the pressure in the lean passage being higher than that in the rich passage.