Toro 51643 Service Manual page 24

Carburetor Operation Fuel Metering & Mixing
(cont'd)
2. The fuel is drawn through the hole in the top of the
main diaphragm chamber and past the high speed
mixture screw. The high speed mixture screw
regulates the maximum amount of fuel
that
can
enter the carburetor throat.
3. The fuel is then drawn past the secondary needle
which is attached to the throttlevalve.
It
moves with
the throttle valve and regulates the amount of fuel
allowed into the carburetor throat in proportion
with the throttle setting.
4. The venturi is the portion of a carburetor throat that
is narrowed in order to increase air velocity. On the
TC1000 carburetor, the venturi size is variable and
is controlled by the postion
of
the throttle valve.
See Figure 12.
THROTTLE
VALVE
Figure 12
5. The vacuum in the venturi area draws the fuel past
the secondary needle jet and into the carburetor
throat.
VENTURI
AIR CORRECTION JET
Figure 13
6.
To better atomize the fuel, an air correction jet was
added. The air correction jet allows filtered air to
enter the carburetor throat perpendicular to the
normal air flow. This action creates turbulence in
the venturi area and helps mix the fuel with air as
it
enters the carburetor throat. See Figure 13.
7.
The air/fuel mixture enters the engine.
Carburetor Operation The Primer System
The TC3000, TC4000 and TC5000 trimmers use a primer
system that ensures fuel is present throughout the fuel
system. When properly used, this primer system should
not induce flooding.
The recommended procedure for priming is as follows:
See Figure 14
CHOKE LEVER
OVERFLOW
TUBE
\
Figure 14
Push the tickler button fully inward.
Manually pump the primer pump until a small
amount of fuel is emitted from the overflow tube.
Stop pumping the primer pump and release the
tickler valve. The engine is now ready to start.
The operation of the primer system is as follows: See
Figure 15.
1. When the tickler valve is depressed slightly, the
2. Depressing the tickler valve fully keeps the inlet
needle unseated and also opens the overflow
needle.
inlet needle is unseated.
13