Dealer Development Center
44
Dealer Development Center
43
Starter Circuit : Constant Velocity Carburettor
1. Plunger Cap
2. Diaphragm Cap
3. Diaphragm Piston Valve
4. Piston Valve with Jet Needle
5. Float Chamber
Air inlet
for choke
Towards
Engine
Function
The function of starter circuit is to provide rich air fuel mixture on starting / cold starting. At cold engine
condition the air is dense also the engine parts are cold enough this does not allow the petrol to
vaporize properly this leads to starting trouble.
Construction
The Starter Circuit consists of a starter jet and a plunger. The starter jet is used to meter the fuel and a
plunger that opens an air passage from the inlet of the carburettor (underneath the diaphragm) which
passes the mixture to the mainfold.
Working
On pulling the choke lever the plunger is lifted by a cable. This uncovers the fuel passage that leads to
the starter jet, air inlet passage and the outlet passage towards the manifold. This creates enough
suction to draw fuel up from the bowl into the mixing chamber (below the plunger). Here the fuel is
mixed with the air and the mixture is drawn into the engine through the outlet passage.
Cut Section View
of Mixing Chamber
Towards
Engine
1. Plunger
2. Mixing Chamber
3. Starter Jet
Pulsar DTS-i UG-III-180cc Training NotesPulsar DTS-i UG-III-180cc Training Notes
1. Pilot Jet
2. Pilot Outlet Hole
3. Butterfly Valve
4. Volume Control
Screw
5. Idling Adjustment
Screw
6. Fuel Inlet
Function
The pilot circuit provides the air fuel mixture at idling when not enough air is being drawn through the
carburettor to cause the main circuit to operate.
Construction
The pilot circuit consists of pilot jet, pilot air jet and volume control screw. The pilot jet meters the fuel
and the pilot air jet meters the air quantity. The volume control (VC) screw controls the amount of air fuel
mixture flowing through the pilot outlet.
Working
As the air enters the pilot air inlet the fuel is metered by pilot jet and air quantity is metered by pilot air
jet. The atomized / vaporized mixture is discharged through the pilot outlet. The pilot outlet is located on
the manifold side of the carburettor. Since the throttle valve is almost at fully closed position, air fuel
mixture is supplied mainly by pilot outlet only. Air fuel mixture volume is adjusted by volume control (VC)
screw and mixture becomes lean when volume control (VC) screw turned clockwise and rich when it is
turned Anticlockwise direction.
Pilot Circuit : Constant Velocity Carburettor
Towards
Engine
Air Inlet
for pilot jet
Working of CarburettorWorking of Carburettor
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