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General
The user must only carry out the maintenance and service
work described in this manual. More extensive work must be
carried out by an authorised service workshop.
Function
•
The carburettor governs the engine’s speed via
the throttle control. Air and fuel are mixed in the
carburettor. The air/ fuel mixture is adjustable. Correct
adjustment is essential to get the best performance
from the chainsaw.
•
The setting of the carburettor means that the engine is
adapted to local conditions, for example, the climate,
altitude, fuel and the type of 2-stroke oil.
•
The carburettor has three adjustment controls:
L = Low speed jet
H = High speed jet
T = Idle adjustment screw
•
The L and H-jets are used to adjust the supply of fuel to
match the rate that air is admitted, which is controlled
with the throttle. If they are turned clockwise the air/
fuel ratio becomes leaner (less fuel) and if they are
turned anti clockwise the ratio becomes richer (more
fuel). A lean mixture gives a higher engine speed and a
rich mixture gives a lower engine speed.
•
The T-screw regulates the throttle setting at idle speed.
If the T-screw is turned clockwise this gives a higher idle
speed; turning it anti-clockwise gives a lower idle speed.
Basic settings and running in
The basic carburettor settings are adjusted during testing at
the factory. Avoid running at a too high speed for extended
periods during the first 10 hours. Rec. idle speed: 2700 rpm
Fine adjustment
When the chainsaw has been “run-in” the carburettor
should be finely adjusted. A qualified person should carry
out the fine adjustment. First adjust the L-jet, then the idling
screw T and then the H-jet.
Conditions
•
Before any adjustments are made, the air filter should
be clean and the cylinder cover fitted. Adjusting the
carburettor while a dirty air filter is in use will result in
a leaner mixture next time the filter is cleaned. This can
give rise to serious engine damage.
•
Do not attempt to adjust the L and H jets beyond either
stop as this could cause damage.
•
Now start the chainsaw according to the starting
instructions and let it warm up for 10 minutes.
•
Place the chainsaw on a flat surface so that the bar
points away from you and so that the bar and chain do
not come into contact with the surface or other objects.
Low speed jet L
Turn the low speed jet L clockwise until it stops. If the engine
accelerates poorly or idles unevenly, turn the low speed jet L
anti-clockwise until good acceleration and idling is achieved.
Fine adjustment of the idling speed T
Adjust the idle speed with the T-screw. If it is necessary to
re -adjust, turn the T-screw clockwise while the engine is
running, until the chain starts to rotate. Then turn anti-
clockwise until the chain stops. A correctly adjusted idle
speed setting occurs when the engine runs smoothly in every
position. It should also be good margin to the rpm when the
chain starts to rotate.
High speed jet H
At the factory the engine is adjusted at sea level. When
working at a high altitude or in different weather conditions,
temperatures and atmospheric humidity, it may be necessary
to make minor adjustments to the high speed jet.
When test run at the factory, the high speed jet is set so that
the engine satisfies the applicable legal requirements while
at the same time as achieving maximum performance. The
carburettor’s high speed jet is then locked using a limiter cap
in the fully screwed out position. The limiter cap limits the
potential to adjust the high speed jet to at most half a turn.
Be sure to adjust the carburettor with the bar chain attached.
1. Stop engine and screw in both H and L needles until they
stop. Never force them. Then set them back the initial
number of turns as shown below.
H needle: 1¼±¼
L needle: 1½±¼
2. Start the engine and allow it to warm up at half-throttle.
3. Turn L needle slowly clockwise to find a position where
idling speed is maximum. Then turn the needle back a
quarter (1/4) turn anti-clockwise.
4. Turn idle adjusting screw(T) anti-clockwise so that the
saw chain does not turn. If idling speed is too slow. Turn
the screw clockwise.
5. Make a test cut and adjust the H needle for best cutting
power, not for maximum speed.
a. L needle
b. H needle
c. Idle adjusting screw
MAINTENANCE
CAUTION If the chain rotates while idling the T-screw
must be turned anti-clockwise until the chain stops
WARNING! Contact our Customer Support
Department, if the idle speed setting cannot
be adjusted so that the chain stops. Do not
use the chainsaw until it has been properly
adjusted or repaired.
CAUTION If the high speed jet is screwed in too far, it
may damage the piston/cylinder.
NOTE
BT-CS-40
