Workshop Manual

REG. CODE
1-5302-509
MODEL N°
50778
DATE OF ISSUE
10.06.99
REVISION 00
DATE
10.06.99
ENDORSED
COMPILER TECO/ATI
56
FUELLING CIRCUIT
XI
140
137
139
138
Cold starting
Enrichment is obtained by shutting off eccentric throttle 2, controlled
by a cam.
An intermediate cam meanwhile partially opens accelerator throttle
1.
Fast idling speed allows the engine to quickly warm up and be
immediately used.
Normal speed
The fuel passes through the reedle valve into the float chamber
where float 12, articulated in the center pivot, regulates reedle 13
opening to keep the fuel itself at a constant level.
The fuel passes from the float chamber through main jet 3 until it
reaches the diffuser tube. Mixed with the air from the calibrated bush
4, the fuel reaches the carburation zone formed by the centering
device and choke 9. A full load enrichment jet increases mixture
enrichment through the opening of a fuel inlet by-pass 10 in the
fuelling circuit controlled by the air system. When the low speed
throttle opens, vacuum reaches under the throttle, the spring acts on
the diaphragm and the valve opens a complementary circuit to the
main jet.
At a high rate, a power enricher 11 adds a a supplementary quantity
of fuel to the engine by the action of vacuum at jet level.
Idling speed
Fuel from the float chamber passes through jet 3 and reaches the
sump of the diffuser tube. A hole transfers the fuel to slow running jet
6 where it is mixed with the air. The fuel flows past the throttle
through the enrichment jet adjuster screw 8. When the throttle opens,
operation progressively passes from the idling circuit to that of
normal speed through the holes on a level with throttle 15, forming
an offtake of the idling circuit (progressive outlet holes).
Pick-up
When the throttle opens, the cam actuated with the throttle rod acts
on lever 17 which pushes diaphragm 18. The fuel passes through a
non-return valve 21 and flows towards jet 19 to be atomized in the
choke. A spring on the diaphragm rod absorbs the quick throttle
openings, prolonging the fuel supply. When the diaphragm returns to
its position, the valve on the jet shuts and the valve on the float
chamber 20 side opens, taking in the fuel which fills the pump
chamber.