Husqvarna 250 PS Workshop Manual page 22

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Fine tuning
First adjust the L needle, followed by the T needle, and
finally the idle screw T. The recommended engine
speeds are as follows:
Max. engine speed11,000 rpm
Idle speed 2,500 rpm
Low speed needle L
Find the highest idle speed by slowly turning the low
speed needle clockwise, then anticlockwise. When you
have found the highest idle speed turn the L needle 1/4
turn anticlockwise.
NOTE! If the chain rotates at idle, turn the T screw
clockwise until it stops.
High speed needle H
The high speed needle affects the power and engine
speed of the pruning saw.
Run the pruning saw at full throttle for about 10 seconds.
Then turn the H needle 1/4 turn anticlockwise.
Run the pruning saw at full throttle again for about 10
seconds and listen for any difference in speed.
Repeat this procedure after turning the H needle a
further 1/4 turn anticlockwise. You have now run the
pruning saw at H=1, H=1 1/4 and H=1. At full throttle the
engine should sound different at each setting.
The H needle is correctly set when the engine "burbles"
slightly. If smoke comes from the silencer and the engine
burbles too much then the mixture is too rich. If the
pruning saw "screams" then the setting is too weak. Turn
the H needle clockwise until the engine sounds right. Do
not exceed the recommended engine speed of 11,000
rpm.
Fine tuning the idle setting T
If it is necessary to adjust the idle setting, turn the idle
screw T clockwise with the engine running until the chain
starts to rotate. Then turn the idle screw anticlockwise
until the chain stops. The idle setting is correct (around
2,500 rpm) when the engine runs smoothly in all
positions and there is a good margin to the speed at
which the chain starts turning.