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.