Idling Speed Circuit; Slow Speed Circuit; Medium Speed Circuit - Vento Phantom R4i Service Maintenance Manual

3. IDLING CIRCUIT:
After starting operation choke is
released, more air starts flowing thru
the venturi. From slow jet fuel is
sucked due to venturi effect. A
separate passage from the air filter
side is coming at the diffuser of the
slow jet for the atomization of fuel in
slow jet. This atomized fuel is
sucked into the venturi as started
above from the slow jet (As shown in
figure). The amount of air for
atomization is regulated by air screw
located at bottom side of the
carburetor body.
4. SLOW SPEEDCIRUIT
Slow speed requires very less
acceleration. Air fuel mixture is being
supplied by slow jet and also from
main jet. This is due to partial
opening of throttle valve, lifts needle
jet upwards. Hence some quantity of
air fuel mixture coming out from
main jet diffuser also mixes along
with slow jet mixture to increase the
mixture quantity as required by
engine.

5.MEDIUM SPEED CIRCUIT

(Economy speed range)
Further acceleration the air fuel
mixture supplied to engine only
from main jet. During this slow jet
stops supplying air fuel mixture
due to venturi effect. Hence air is
drawn to main jet through metered
air jet (Brass tube) for better
mixing of fuel with air in the main
jet diffuser. Main
supplying air fuel
economy range i.e. more air with
less quantity of fuel as per engine
requirement.
VENTO MOTORCYCLES
jet started
mixture in
Rev no.01/ page 53of 84