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CHAPTER 9 Two-Stroke Engine Troubleshooting and Evaluation
Copyright Goodheart-Willcox Co., Inc.
When fuel is poured into the fuel tank, the
phase-separated layer remains at the lowest
part of the tank. The weighted fuel filter also
falls to the lowest part of the tank. So, when
the engine is running in different positions, the
fuel filter and phase-separated layer are always
together. Two-stroke oil does not dissolve into
the phase-separated layer. When the fuel filter
pulls any of this layer into the engine, the engine
will have little to no lubrication. The water con-
tent of the layer washes off lubrication from the
engine’s internal surfaces. The engine will pro-
duce the same scoring as a raw gas failure.
Test the Customer’s Fuel
To determine if the fuel is fresh, marginal, or
stale, put the tip of a gasoline test swab into
the fuel for 10 seconds. The swab has a chem-
ical that detects stale fuel. Remove it and let it
dry for one to two minutes. Match the color of
the test swab with the color on the container.
The test swab in Figure 9-45 indicates that the
fuel being tested is marginal. This fuel being
tested came from a chain saw that would not
start. When fresh fuel was added, the chain saw
started and ran.
Next, test the fuel for the percentage of
alcohol. The test vial for the percentage of alco-
hol is calibrated with a water level mark and a
fuel level mark. The vial in Figure 9-46 has a
line labeled “Add water to this line.” Add plain
water to this mark. Add the customer’s fuel to
the line marked “Add gasoline to this line.” Seal
the vial and shake. During the shaking process,
ethanol in the fuel will bond with the water, and
the ethanol will phase separate and sink to the
bottom of the vial. The lines above the water
level line indicate the percent of alcohol in the
fuel. The fuel in the vial in Figure 9-46 contains
approximately 6% ethanol.
Next, test for the presence and percentage of
two-cycle oil. Put a sample of the customer’s fuel
into a small vial. Add an equal amount of the
B3C Solutions 2-Cycle Oil Test solution. Shake
well. Compare the color of the liquid with the
charts for red or green two-stroke oil.
Discuss with the customer the problems
related to the fuel. If the engine being evaluated
had fuel in the tank when it came in for repair,
this fuel was saved into a sealed container at the
beginning of the engine evaluation process. The
fuel needs to be tested for staleness, percent of
alcohol, and presence of premixed oil. After-
ward, the results of the fuel testing could be
shared with the customer to help purchase and
store fuel properly in the future. Guidelines for
properly maintaining the fuel system are pub-
lished in the equipment’s owner’s manual. The
Goodheart-Willcox Publisher
Figure 9-45. The test swab indicates the condition
of the fuel being tested. The swab shown here indi-
cates the fuel is not fresh, but marginally stale.
Step 3:
Seal and shake
Step 4:
Read ethanol
percentage
Step 2:
Add customer’s
fuel to this line
Step 1:
Add water to this line
Goodheart-Willcox Publisher
Figure 9-46. A test vial is marked for a water
level (bottom line) and a fuel level (top line). Add
water first and then the fuel. Shake. The ethanol
bonds with the water and phase separates. The
increase in clear liquid above the water level line is
the percentage of ethanol in the fuel.