Page 26 - Demo

Page 26.Alvis Three Litre Shop Manual - T.A. 21 and T.C. 21Generaal Fuuncti ction off tthe CaarbuburettttorAir is drawn downwards through the choke tubes (K) creating a depression or suction on the spraying assembly exit holes (S).The petrol, calibrated by the main jets (Gg) which are screwed into holders (Y), is lifted from the well at the base of the spraying assembly and simultaneously is emulsified and %u2018corrected%u2019 by air passing through the %u2018correction jets%u2019 (a) and out of the base holes of the emulsion tubes beneath.The resultant emulsion emerges from the holes (S) and is finally disintegrated by the main air stream, the volume of which is controlled by the size of the choke tubes before passing to the engine via the throttle butterflies (V).Accccelerati atingg DDevic viceWhen the throttles are suddenly opened the mixture is enriched by petrol sprayed into the air stream by the accelerator pump through the two injectors (i).Prior to depressing the accelerator pedal, petrol is drawn into the pump via nonreturn valve (Cl) by the expanding action of the spring (r) on the membrane (M). Opening the throttles ejects petrol from the pump via the calibrated %u2018speed%u2019 jets (Ca) which control the rate of discharge from the accelerating device.Caarbuburati ation FauaulttsWhen carburation trouble occurs with a carburettor which has previously been functioning satisfactorily the fault can usually be traced to dirt or water in the jets or jet channels. Jets should on no account be cleaned out with wire but should be washed in petrol and blown out.Flooding may be caused by grit on the needle valve seating or a punctured float, both points can be checked by removing the carburettor top cover which is retained by four hexagon headed screws.It is not usual for grit to get on to the needle seating provided the filter is in good condition. Should this occur however, remove the valve, blow it out, and test by General view of S.U. carburettors