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491
High Altitude Operation
This engine has been factory adjusted to maintain satisfactory starting and
durability performance up to 335 m (1,100 ft.) above sea level (ASL)
(96.0 kPa). To maintain proper engine operation above 335 m (1,100 ft.)
ASL the carburetor might need to be adjusted by an authorized service
dealer.
If the engine is adjusted for operation above 335 m (1,100 ft.) ASL,
the carburetor must be readjusted when operating the engine below
335 m (1,100 ft.) ASL, otherwise severe engine damage can result.
1.
Before adjusting carburetor clean or replace air filter and muffler spark
arrester screen.
2.
Make sure the bar and chain are properly adjusted.
3.
Start engine and run several minutes to bring to operating temperature.
Flash choke twice during warm-up to clear any air from the fuel system.
4.
Stop engine. Turn "H" High Speed needle counterclockwise (CCW) to
stop. Turn "L" Low Speed needle midway between full clockwise (CW)
stop and CCW stop.
5.
Idle Speed Adjustment:
• Start engine, turn Idle speed adjustment screw "T" CW until the saw
chain begins to move, then turn screw out CCW until the saw chain
stops moving. Turn screw out, CCW, an additional 1/4 turn.
When carburetor adjustment is completed, the saw chain
should not move at idle, otherwise serious personal injury can
result.
6.
Accelerate to full throttle for two to three seconds to clear any excess
fuel in the engine, then return to idle. Accelerate engine to full throttle to
check for smooth transition from idle to high speed. If engine hesitates
turn "L" needle CCW 1/8 turn and repeat acceleration. Continue
adjustment until smooth acceleration results.
7.
Check idle speed and reset if necessary as described in item 5. If a
tachometer is available idle speed should be set to value listed on
specifications page.
X7503312606
© 02/24 ECHO Incorporated
MAINTENANCE
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