CARBURETTOR-8

Assemble and disassemble of Carburettors For 40 PAIO – Carburettors: Solex Down Draught Carburettors

The operation of this starter system is also by rotation of the Starter valve which is connected to the dash board control in the same way. (In this type we have two Discs, one for Air control and the other for petrol control) In-this system we have two positions of operation (viz.) Starter full open position and warm up position. Starter full open position

(a) During very cold weather (as these type of carburettors are fitted mainly to vehicles used by Army), when the choke knob is pulled fully away from dash board, it opens the disc valve. Now when the engine is cranked, due to suction created at starter discharge hole, the system draws air through float chamber cover, starter air bend and the small orifice (only little air for atomisation, as extreme cold conditions call for a complete rich mixture) and petrol via starter petrol jet, and passed through the petrol control valve. Now petrol is emulsified and the mixture passes through the starter discharge holes into the engine.

Starter Warm up position

In extreme cold conditions once the engine is started, a progressive fast idle is provided in this system for flexible control of cold engines.

In operation the starter provides a progressively weaker mixture as the dash board control is moved from the intermediate to full in position. This movement adjusts the mixture strength and gives the fast idling speed required to suit a warming engine and also provides a slightly rich mixture for quick drive away whilst the engine is still cold.

In the ‘Intermediate’ position which is located by a spring loaded ball under the starter lever, the dished hole in the petrol regulating valve is getting communicated to circuit from starter petrol jet. The orifice at the dished portion (smaller in size) reduces fuel input from starter petrol jet and combined with air drawn into channel shown as Air above throttle spindle, supplies a weaker mixture.

Rotation of valve as the dash board control is pushed home progressively reduces the starter discharge, thus causing the engine to slow down and the strength of the mixture is adjusted to suit the new conditions as the engine warms up. When the knob is fully closed the device is put out of action by the disc valve which closes the concerned petrol and Air orifices.

Driving away:

On opening the throttle with a cold engine, extra enrichment is provided by suction then being brought directly into the channel marked ‘Air’ above throttle, drawing mixture from the petrol channel. The degree of enrichment progressively diminishing as the disc valve is progressively closed.

THE SLOW SPEED JET SYSTEM

During slow speed, the engine normally requires a relatively richer mixture compared to what it would require under cruising conditions. The slow speed system consisting of the idling and the By-pass (transition) circuits, takes care of these requirements. The idling circuit comes into operation when the throttle valve is practically closed, and the By-pass circuit when the throttle is slightly opened. Usually there is a slight difference from engine to engine in the requirements of idling mixture and this changes with age and engine parameters like ignition timing, compression pressure etc. To take care of these variables Volume Control screw is provided to alter slightly the air-fuel mixture. Opening of the throttle required for idling speed is controlled by the slow running adjustment screw.

IDLING CIRCUIT:

When the engine is idling, suction felt underneath the throttle causes petrol to flow from the emulsion well to the Pilot Jet. The petrol, after being metered by the Pilot Jet combines with air metered by Pilot air bleed. The mixture then moving down to the volume control screw and through the discharge orifice in to the engine. With a given size of Pilot Jet and air bleed the volume of the idling mixture is controlled by screwing the volume control strew in or out, which respectively permits a reduced or increased quantity of air fuel mixture passing through the idling discharge orifice. For correct setting of the idling it is necessary to use both means of adjustment, i.e., volume control screw for mixture strength and slow running adjustment screw for speed.