Jonsered Chainsaw Carburetor Adjustment Guide: How to Adjust Your Chainsaw for Peak Performance

MAINTENANCE

Carburetor

Your Jonsered product has been designed and manufactured to specifications that reduce harmful emissions.

After your unit has been run 8-10 tanks of fuel the engine has broken in. To ensure that your unit is at peak performance and producing the least amount of harmful emissions after break in, have your authorized servicing dealer, who has a revolution counter at his disposal, to adjust your carburetor for optimum operating conditions.

Functioning, Basic setting, Final setting

!WARNING! Do not start the saw without the bar, chain and clutch cover (chain brake) assembled. If you do, the clutch might come loose and cause severe injuries.

Operation

•The carburetor governs the engine speed via the throttle. Air/ fuel are mixed in the carburetor. The air/fuel mixture is adjustable. To take advantage of the engine’s optimal output the setting must be correct.

•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.

Conditions

•Before any adjustments are made the air filter should be clean and the cylinder cover fitted. Adjusting the carburetor while a dirty air filter is in use will result in a leaner mixture when the filter is finally cleaned. This can give rise to serious engine damage.

•Carefully turn the L needle to the mid point and H needle counter-clockwise against the stop.

•Do not attempt to adjust the needles beyond the stops as damage can occur.

•Now start the saw according to the starting instructions and run it warm for 10 minutes.

NOTE! If the chain rotates the T screw should be turned counter-clockwise until the chain stops.

•Place the saw 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 needle L

Turn the low speed needle L clockwise until the stop. If the engine has bad acceleration or erratic idling, turn the L needle counter-clockwise until good idling and acceleration.

NOTE! If the chain rotates in the idling position, turn the idling speed screw T counter-clockwise until the chain stops.

•The carburetor has three adjustment possibilities:

L = Low speed jet. H = High speed jet.

T = Adjustment screw for idling.

T	H
L

Final setting of the idling speed T

Adjust the idling speed with the screw T. If it is necessary to re- adjust, first turn the idle speed adjusting screw T clockwise, until the chain starts to rotate. Then turn, counter-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.

!Contact your servicing dealer, if the idle speed setting cannot be adjusted so that the chain stops. Do not use the saw until it has been properly adjusted or repaired.

•The fuel quantity required in relation to the air flow, provided by opening the throttle, is adjusted by the L and H-jets. If they are screwed clockwise the air/fuel ratio becomes leaner (less fuel) and if they are turned counter-clockwise the ratio becomes richer (more fuel). A leaner mixture gives a higher engine speed and a richer mixture give a lower engine speed.

•The T screw regulates the idling speed. If the screw T is turned clockwise this gives a higher idling speed; counter- clockwise a lower idling speed.

Basic setting and running in

The carburetor is set to its basic setting when test run at the factory. The basic setting should be kept during the machine‘s first working hours. Thereafter the carburetor should be finely adjusted. Fine adjustment should be carried out by a skilled technician.

NOTE! If the chain rotates while idling the T screw should be adjusted counter-clockwise until it stops.

Recommended idling speed: 2 700 rpm.

!Contact your servicing dealer, if the idle speed setting cannot be adjusted so that the chain stops. Do not use the saw until it has been properly adjusted or repaired.

Fine adjustment

•When the saw has been ”run-in” the carburetor should be finely adjusted. The fine adjustment should be carried out by qualified person. First adjust the L-jet, then the idling screw T and then the H-jet.

High speed needle H
The high speed needle H
influences the power of the
saw. A too lean adjusted high
speed needle H (high speed
needle H turned too much
clockwise) gives overrevs and
damages the engine. Do not
allow the engine to run at full
speed for more than 10
seconds. Turn the high speed
needle H counter-clockwise	H
until the stop. If the engine
runs roughly, turn the high
speed needle slowly the
minimum amount clockwise
until the engine runs smoothly.

The high speed needle H is correctly set when the saw ”4- cycles” a little. If the saw ”whistles” the setting is too lean. If there is too much exhaust gas at the same time as the saw ”4- cycles” much, the setting is too rich. Turn the high speed needle H until the setting sounds correct. NOTE! For optimum setting of the carburetor, contact a qualified servicing dealer who has a revolution counter at his disposal.

Correctly adjusted carburetor

A correctly adjusted carburetor means that the saw accelerates without hesitation and the saw preferably 4-cycles a little at max speed. Furthermore, the chain must not rotate at idling. A too lean adjusted low speed needle L may cause starting difficulties and bad acceleration. A too lean adjusted high speed needle H gives lower power=less capacity, bad acceleration and/or damage to the engine. A too rich adjustment of the two speed needles L and H gives acceleration problems or too low working speed.

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