Bajaj pulsar DTS-i, Service Station Manual

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CARBURETTOR CIRCUITS
Pulsar 150/180 DTS-i
Service Station Manual
83
Dealer Development Center
Akurdi Pune
Towards
Engine Air Inlet
for main jet
Main Circuit :
Constant Velocity Carburettor
1. Piston Valve
3. Jet Needle
4. Needle Jet
5. Jet Holder
2. Piston Valve Diaphragm
Function
The Main Circuit provides air fuel mixture by lifting
up the piston valve in direct proportion to the
engine demand. This assures the correct venture
size & air velocity throughout the mid range
operation of the engine.
Construction
This circuit consists of jet needle, needle jet and
main jet. To assist in atomization an air bleed circuit
is incorporated in the main metering system and it
aids fuel vaporization by introducing the air into the
fuel before it enters the main air stream.
The piston valve movement is controlled by spring and carburettor venture vacuum which is generated below
the piston valve diaphragm.
When the butterfly valve is opened and air flow through the venturi increases, the air pressure in the venturi
(and the upper chamber) decreases.
As the atmospheric pressure in the bottom chamber is greater than the venturi pressure above the
diaphragm, the piston valve along with jet needle is pushed up and more air fuel mixture is drawn into the
engine from main jet through needle jet into the main air stream.
When the butterfly valve is closed, air flow through the venturi decreases; air pressure in the venturi
increases and approaches atmospheric pressure, & the spring pushes the piston valve along with jet needle
down.
Working