Jonsered FC 2255 - Manual (Page 28)

MAINTENANCE
28 – English
Carburetor
Your Jonsered product has been designed and
manufactured to specifications that reduce harmful
exhaust fumes. The engine will be run in after it has used
8-10 tanks of fuel. To ensure that the engine runs at peak
performance and produces as little harmful exhaust
fumes as possible after the running-in period, ask your
dealer/service workshop (which has a rev counter for this
purpose) to adjust your carburettor.
Carburetor adjustment
The carburettor can be designed in different ways,
depending on the existing environmental and emissions
legislation. Some machines are equipped with movement
limiters on the carburettor’s adjuster screws. These limit
the adjustment range to a maximum of 1/2 turn.
Function
• The carburetor governs the engine’s speed via the
throttle control. Air and fuel are mixed in the
carburetor. The air/fuel mixture is adjustable. Correct
adjustment is essential to get the best performance
from the machine.
• The setting of the carburetor means that the engine is
adapted to local conditions, for example, the climate,
altitude, fuel and the type of 2-stroke oil.
• The carburetor 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 screwed
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 setting
• The basic carburetor settings are adjusted during
testing at the factory. The basic setting is richer than
the optimal setting and should be maintained for the
first few hours the machine is in use. The carburettor
should then be finely adjusted. Fine adjustment
should be carried out by a skilled technician.
CAUTION! If the cutting attachment rotates when the
engine is idling the idle adjustment screw T should be
turned anti-clockwise until the cutting attachment stops.
Rec. idle speed: See the Technical data section.
Recommended max. speed: See the Technical data
section.
Fine adjustment
When the machine has been ”run-in” the carburetor
should be finely adjusted. The fine adjustment should
be carried out by a qualified person. First adjust the L-
jet, then the idling screw T and then the H-jet.
Conditions
• Before any adjustments are made, make sure that the
air filter is clean and the air filter cover is fitted. If you
adjust the carburettor when the air filter is dirty it will
result in a leaner mixture when the filter is finally
cleaned. This can lead to serious engine damage.
• Carefully turn both jets, L and H, so that they are
midway between fully screwed in and fully screwed
out.
• Do not attempt to adjust the L and H jets beyond either
stop as this could cause damage.
• Now start the machine according to the starting
instructions and let it warm up for 10 minutes.
CAUTION! If the cutting attachment rotates when the
engine is idling the idle adjustment screw T should be
turned anti-clockwise until the cutting attachment
stops.
!
WARNING! The complete clutch cover
and shaft must be fitted before the
machine is started, otherwise the clutch
can come loose and cause personal
injury.
1/2
1/2
H
L
!
WARNING! If the idle speed cannot be
adjusted so that the cutting attachment
stops, contact your dealer/service
workshop. Do not use the machine until
it has been correctly adjusted or
repaired.