SECTION
1
CARBURETOR
Carburetor Operation
The carburetor used on the TC3000, TC4000 and the
TC5000 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 carburetor,
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 positive 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 accomplished by a
passage which leads from the lower crankcase to a point
just below the intake port. See Figure
6.
PULSE
PASSAGE
Figure
6
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 Figure
7.
n
PULSE PASSAGE
PULSE
HOLE
Figure
7
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 Figure
8.
FUEL
FUEL
PUMP
COVER
INLET
CAVITY
Figure
8
1.
The oulet flapper valve
is
drawn toward the pump
cover. This seals the outlet passage to ensure that
fuel is drawn only through the fuel inlet.
11
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