198
Two-Stroke Engines
Copyright Goodheart-Willcox Co., Inc.
At this point in the engine evaluation, the fuel
filter has been removed from the fuel line con-
nected to the carburetor. This is the appropriate
time to perform the first test for evaluating the
carburetor.
Carburetor Evaluation
Test the fuel line, carburetor fuel pump, and nee-
dle by attaching a pressure tester to the end of
the fuel line where the fuel filter was removed.
See Figure 9-35. Pressurize the fuel line to 7 to
10 psi. Once you are done pumping, the pres-
sure should remain constant. If the pressure
holds steady, the fuel line, pump side of the car-
buretor, and inlet needle are leak-free.
Next, test the purge prime system if the engine
is equipped with one. While the gauge is holding
pressure, depress and release the primer bulb
several times. See Figure 9-36. Notice the nee-
dle on the gauge. The needle on the gauge should
drop slightly each time the bulb is released. This
indicates that purge prime check valves, the
carburetor’s metering chamber check valves,
and the accelerator pump O-ring are working
properly.
Switch the pressure-vacuum tester to vacuum
mode. Continue depressing and releasing the
primer bulb to pull about 10 inches vacuum. The
carburetor should hold the vacuum. This means
Should hold
1.5–5.5 psi Vent
Goodheart-Willcox Publisher
Figure 9-32. The tank vent should hold 1.5 to
5.5 psi pressure. It should not hold a vacuum.
Fuel filter Hook
Goodheart-Willcox Publisher
Figure 9-33. Use a hook to pull the fuel pick-up
line and filter out of the tank.
Blocked filter Vacuum
Goodheart-Willcox Publisher
Figure 9-34. If the fuel filter holds vacuum, it is
clogged and must be replaced.
Pressure should hold Fuel pick-up line
Goodheart-Willcox Publisher
Figure 9-35. Attach a pressure tester to the fuel
line. Pressurize the fuel line to 7 to 10 psi. If the
pressure does not drop, then there is no leak in
the fuel line itself or the pump side of the carbure-
tor. The needle is not leaking, but holding the 7 to
10 psi pressure.