Carburetor Operation - Toro TC 1000 Service Manual

SECTION 1
Carburetor Operation
The carburetor for the TC1000 is a diaphragm
style carburetor. It uses alternating pulses from
the crankcase to pump fuel from the fuel tank to
the carburetor.
To adequately describe the function of the car-
buretor, it is necessary to break its operation
down into three systems:
-The Diaphragm Pump
Fuel Metering and Mixing System
The Primer System
Carburetor Operation The Diaphragm Pump
The diaphragm pump requires alternating posi-
tive and negative air pressures working upon it in
order to fluctuate and perform a pumping
function. The source of the positive and negative
pressures is the lower crankcase where these
pressures are alternately being created by the up
and down movement of the piston.
Transfer of these pressure pulses is accom-
plished by a passage which leads from the lower
crankcase, to a point just below the intake port.
See Fig. 7.
PULSE
PASSAGE
Figure 7
From there, the passage leads through the intake
flange and into the carburetor. It /terminates in
the diaphragm chamber at a point called the
pulse hole. See Fig. 8
10
PULSE PASSAGE PULSE HOLE
Figure 8
The pulses vary with the movement of the piston.
As the piston moves upward, vacuum is created
which pulls the diaphragm toward the pulse
hole. This movement results in three things
happening on the pump cover side of the
diaphragm. See Fig. 9.
1.
The outlet flapper valve is drawn toward the
pump cover. This seals the outlet passage to
ensure that fuel is drawn only through the
fuel inlet.
2. The inlet flapper valve is pulled open to allow
fuel toflowfrom thefuel line into thefuel inlet
cavity.
3. Fuel is drawn into the fuel pump cavity.
FUEL PUMP
FUEL INLET
COVER
CAVITY
. _ I
Figure 9