25 CS-450
CARBURETOR ADJUSTMENT
Every unit is run at the factory and the carburetor
is set in compliance with Emission Regulations. In
addition, the carburetor is equipped with “H” (High
Speed) and “L” (Low Speed) needle adjustment
limiters that prevent settings outside acceptable
limits.
1. Before adjusting carburetor clean or replace air
lter and mufer “Spark Arrestor Screen”.
2. Make sure the bar and chain are properly ad-
justed.
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” speed needle counterclockwise (CCW)
to stop.
Turn “L” speed needle midway between full
clockwise (CW) stop and CCW stop.
5. Idle Speed Adjustment:
• Start engine, turn “Idle” speed adjustment
screw CW until the saw chain begins to turn,
then turn screw out CCW until the saw chain
stops turning.
Turn screw out, CCW, an additional 1/4 turn.
6. Accelerate to full throttle for 2 - 3 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 2700 RPM.
WARNING
Cutting attachment must not move when unit
is idling.
CAUTION
When starting, idling adjustment speed
should be adjusted not to rotate the saw
chain. Correct idle speed is adjusted 2700
RPM. Or 1/4 turn CCW from the point the
chain stops moving.
When you experience trouble with the
carburetor, contact your dealer.
Idle adjusting screw
Low speed needle (L) High speed needle (H)
High Altitude Operation
This engine has been factory adjusted to maintain
satisfactory starting, emission, and durability
performance up to 1100 feet above sea level (ASL)
(96.0 kPa). To maintain proper engine operation
and emission compliance above 1100 feet ASL
the carburetor may need to be adjusted by an
authorized ECHO service dealer.
IMPORTANT
If the engine is adjusted for operation above
1100 feet ASL, the carburetor must be
readjusted when operating the engine below
1100 feet ASL, otherwise severe engine damage
may result.
Engine Break-In
New engines must be operated a minimum dura-
tion of two tanks of fuel break-in before carbure-
tor adjustments can be made. During the break-in
period your engine performance will increase and
exhaust emissions will stabilize. Idle speed can
be adjusted as required.