In concept the system remained similar throughout production. The atomiser is arranged in the transfer port and a fixed proportion of fuel is thus added to each air charge. The quantity of air charge is regulated by a sliding valve in the transfer port which is moved by the weight and spring governer fixed to the starting side flywheel.  Fuel ratio adjustment is by a needle valve between the fuel chamber and the atomiser.

However this was achieved by a wide variety of methods.

The earliest models are fitted with a one piece carburettor with vertical mixture needle and a float designed to stop fuel supply when the desired level is reached. A crude atomiser is used which visually resembles a funnel and is an annular flow-accelerator around a single jet. The fuel is supplied by a piston pump, in the reed valve housing, which is operated by crankcase compression and has a foot valve on the feed tube.  A draincock allows paraffin to be returned to the tank before starting on petrol. The early atomiser has poor efficiency at hand-cranking speed and to overcome this a priming cup is fitted in the top flange of the crankcase on the starting side.  The air entering the reed valve is also regulated by a rotating shutter operated by a lower extension of the governer lever. An adjustable governer override ("Speeder") is fitted and allows some user variation of the engine speed. Early needle-valve knobs are marked 1-4hp so the intent must have been to allow the engine to operate smoothly over a wide variation of required outputs.

After 1000-1200 engines, in about 1915, some detail changes were made. An overflow was fitted in the side of the carburettor body presumably in an attempt to deal with over-enthusiastic pumping which overcame the merrily jiggling float! Initially it seems that the overflow ran straight to the base tank thus producing a tank with 4 holes rather than the usual three. The overflow was soon redirected into the normal fuel return pipe and the extra drilling deleted.  Control of the air valve on the reed valve housing and the governer arm lower extension  were deleted (presumably as it served little purpose) although the brass valve remained for some time.

At the same time as the "Jellymould" head was introduced  a second chamber was added to the carburettor which remained as previously except that it is a separate casting from the transfer port cover. The second chamber served as an oil dripper and allowed the glass oiler in the reed valve boss to be deleted. The unused boss remained in  the housing throughout "Jellymould" production. The top of the reed valve housing acquired a hole for the dripper pipe.The reason for the change is unknown but perhaps customers complained about bending down between the flywheels to refill or adjust the oiler?     At this time the priming cup was moved to the right front of the cylinder head flange.

With the "Victory" head arrived the familiar carburettor, with its improved atomiser and the patent diaphragm pump. Both the speeder and the priming cup   disappear at the same time. Caution: The change from Jellymould to Victory is one of the most protracted with batches of both being overlapped for perhaps a year.