Toro GTS 120 Service Manual page 8

carburetor causes atmospheric pressure to push
rawfuel from the float bowl into theair stream, where
it breaks up into a fine spray, or becomes atomized,
and mixes with the air stream (Figure 1-5).
Float Bowl To Engine
Figure
1-5
Operation
When starting the engine, an extra rich mixture is
required. The choke plate is closed by the opera-
tor to provide an approximate 8:1 ratio of fuel to
air for this rich mixture. Closing the choke plate
further reduces the air pressure area in the
venturi to increase the fuel drawn into the car-
buretor bore. In this condition fuel is drawn from
the float bowl through the pilot system ports as
well as the main discharge tube to achieve the
proper starting mixture (Figure
1-6).
Pilot Jet
Pilot System
Pilot Air Fitting
COLD START
Figure
1-6
Fuel atomization becomes more efficient, due to
heat, once the engine has reached normal
operating temperature. As a result, the engine
does not require the rich mixture it did for
starting and the choke plate must be moved to
the open position. The engine speed is now
regulated by the throttle plate. In no load condi-
tions a small portion of the fuel may be drawn
from the main discharge tube, however the pri-
mary fuel supply is drawn from the pilot circuit.
1-4
Air passing through the pilot jet from the pilot air
fitting draws fuel out of the pilot jet orifice from
the float bowl. This fuel pre-mixes with the
incoming air, then is discharged into the car-
buretor bore where the fuel becomes atomized
(Figure
1-7).
NO
LOAD
Figure
1-7
As the throttle plate is opened to compensate for
loads the engine is being placed under, the main
discharge tube becomes the main source of fuel.
Opening the throttle plate increases the flow of
air through the venturi and strengthens the low
pressure area at the main discharge tube. Fuel
discharge increases at the main discharge tube
as
it
decreases from the pilot
system. Air is
drawn from the air correction jet through holes
along the length of the main discharge tube. This
pre-mixes air with the fuel before it enters the
carburetor bore for more efficient atomizing of
:he fuel (Figure
1-8).
/pilot System
Float Bowl
UNDER LOAD
Figure 1-8