184
Two-Stroke Engines
Copyright Goodheart-Willcox Co., Inc.
looks like it is good condition, the blades are
rusted together from several years of sitting.
The preliminary inspection may reveal a
problem that is the cause of the customer’s com-
plaint. It is important for the repair technician
to record each of the problems found.
Q uick Tests on the Engine
Reducing repair time on two-stroke equip-
ment is important because it keeps the custom-
er’s repair expense down. Having the following
troubleshooting aids on hand will help reduce
repair time:
• Fresh premix.
• New spark plug.
• Spark tester.
• Spark plug gap feeler gauge.
• Compression gauge.
Performing the following tests in the
sequence shown will help you quickly identify
the problem:
• Evaluate the engine’s fuel delivery system.
• Check secondary compression.
• Check for spark.
• Perform lower end pop-off test.
• Perform upper end pop-off test.
Evaluating the Fuel Delivery System
Evaluate the engine’s fuel delivery system by per-
forming a quick examination of the customer’s
fuel; testing the fuel filter, fuel line and carbure-
tor purge system (if the engine has one). Then,
replace the customer’s fuel with known good
fuel and attempt to start the engine.
Pour the fuel from the customer’s fuel tank
into a container so the entire contents of the
tank can be examined. If the engine has a purge
system, pump the bulb several times to evac-
uate fuel from the carburetor, and empty the
tank again. Observe the fuel in the container
for contaminants, water, or any problems that
would prevent the engine from starting or run-
ning. The fuel in Figure 9-4 shows evidence of
debris, as well as water. Debris can be as large
as visible particles and as small as dust. Water is
heavier than the fuel and sinks to the bottom of
the fuel, forming a bubble or puddle. As a quick
test, carefully smell the fuel to determine if the
fuel is stale.
Stale fuel smells like old varnish or nail pol-
ish. The gasoline will have a sour smell very
different from fresh fuel. The fresh-fuel-smell
is what a person smells when putting gasoline
into their vehicle at the fuel pump. Gasoline that
smells other than fresh has become stale.
Inspect the customer’s fuel for presence of pre-
mixed oil. Fuel with a blue or red tint, Figure 9-5,
most likely contains premixed oil. Save the fuel
Water bubble
Debris
Goodheart-Willcox Publisher
Figure 9-4. Debris is any contaminant present in
the fuel. Water looks like a bubble or puddle.
Goodheart-Willcox Publisher
Figure 9-5. The colors of red or blue tend to indi-
cate the presence of two-cycle oil. The fuel in the
bottle on the left does not contain oil.