Specifications

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Tips from the Shop
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While a bench test is the
best way to diagnose and repair
an air leak, the following simple
test may help you. While it
may not tell you exactly what
the problem is, you can easily
learn what it is not, and this can
save both money and time.
If you have access to a good
running spare saw of the same
model as the saw giving you
trouble, remove the carburetor
from the good running saw.
Install the known good carbure-
tor on the problematic saw and
test run it. If the loaner carbu-
retor fixes the problem, you
know the carburetor on your
problematic saw is the culprit.
On the other hand, if the saw
still has the same symptoms
after running it with what you
know is a good carburetor, your
saw's original carburetor is
probably OK. You likely have
some other problem -- like an
air leak.
Why Air Leaks Harm Saw
Engines
When a saw has a slight air
leak, the problem can some-
times be masked by setting the
carburetor more rich. While
this can provide temporary
relief, it is not a good solution
because most leaks don't leak
the same amount of air all the
time. When an engine's air/
fuel mix varies, erratic opera-
tion is the result. Secondly,
even if you could compensate
for an air leak with a rich carbu-
retor adjustment, air leaking
into your saw's engine is unfil-
tered. So while the air/fuel mix-
ture may be controllable on a
saw with a slight air leak, debris
getting into the engine is not.
Never ignore an air leak if
you suspect one. Not attending
to an air leak can cause a lean
seizure. When this occurs, air
leaking into the saws engine
makes its air/fuel mixture get
lean. This lean condition some-
times causes the piston to try to
weld itself to the cylinder wall.
This ruins the piston and the
saw's cylinder -- an expensive
repair.
Today's Saw Engines Are
Less Tolerant Of Air Leaks
Today's saw engines are
built to run lean, because lean
burning engines produce fewer
unburned hydrocarbons -- less
emissions. These new saws
have additional cooling capac-
ity as well as other features that
allow them to run well and per-
form this way, however since
they already run lean, even a
slight air leak can push them
over the edge.
continued from page 107 Today's rev-limiting igni-
tion systems are another way
manufacturers keep lean run-
ning engines from over-speed-
i n g , a n d t h i s i s g o o d .
Unfortunately, this can also-
mask the early signs of an air
leak making it harder to detect.
Our Advice
• When frustrated by what you
believe is ongoing carburetor
problems, make sure the root
cause is not an air leak.
• If you have a saw with symp-
toms of an air leak, have it
checked. Unfiltered air and
extra-lean running conditions
can permanently damage your
saw's engine.
• When repairing damage after
an accident, look closely for
damage that could cause an air
leak.
• When repairing damage from
a seizure, check for an air leak.
Seizure repair is expensive --
something you only want to
pay for once.
Conclusion
We hope this information is
helpful and gives you working
knowledge of how an air leak
affects the performance of a pro
saw. We realize we have just
touched the surface on much of
this information, so please con-
tact us if you have questions.
You can count on for straight
and informed talk on pro saws...
That’s why we’re the Pro’s
Choice.
“The Pro’s Choice”
The siezure damage on this piston
was ultimately casued by an air
leak.
The seal behind the flywheel some-
times fails and causes an air leak.