This is an Amal type 4-127, which is fitted as standrad with a size 70 main jet, a type 4 No. 5 throttle valve (marked 4 /5) and No. 4 throttle needle. The throttle needle is set for normal purposes with the fixing clip in the middle groove. The carburetter is provided with a pilot air adjusting screw, which is screwed into the mixing chamber body horizontally just behind the oil pump control rod. The correct adjustment for this screw varies with individual engines, but is usually from 1 to turns open from the fully closed position. The mixture is enriched by screwing in the screw and weakened by screwing it out. The fuel consumption may become heavy if the pilot air adjustment is too rich. For further particulars, see the instruction leaflet issued by the manufacturers of the carburetter.