Carburettor
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 carburettor governs the engine speed via the throttle. Air/fuel are mixed in the carburettor. The air/fuel mixture is adjustable. To take advantage of the saw’s maximum output the setting must be correct.
•The satisfactory operation of a catalytic converter depends, among other factors, on the correct adjustment of the carburettor. Follow carefully the instructions below, using a tachometer to check engine speed.
•Adjusting the carburettor means the engine is adapted to local operating conditions, e.g. climate, altitude, petrol and the type of 2-stroke oil used.
LH
• The carburettor has three adjustment possibilities: L = Low speed jet.
H = High speed jet.
T = Adjustment screw for idling.
T
•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 anti-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; anti-clockwise a lower idling speed.
WARNING! The catalytic converter muffler gets very hot during and after use. This also applies during idling. Be aware of the fire hazard, especially when handling the saw near flammable substances or vapours.
Basic setting and running in
The carburettor is adjusted to a basic setting when the saw is tested at the factory. The basic setting is: H = 1 turn respective L = 1 turn.
To provide the engine’s components with a good level of lubrication (running in) the carburettor should be set for a richer fuel mixture for the first 3-4 hours of operating. To obtain this adjust the speed 6-700 rpm under the recommended max. speed.
If you do not have the possibility to check the speed using a tachometer the H-jet should not be set for a leaner mixture than that stated for the basic setting.
The recommended speed should not be exceeded. NOTE! If the chain rotates while idling the T screw should be adjusted anti-clockwise until it stops.
Fine adjustment
•When the saw has been ”run-in” the carburettor 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. The following engine speed applies:
| Max. speed | Idling speed |
346XP: | 14 200 rpm | 2 700 rpm |
351: | 12 500 rpm | 2 700 rpm |
Changing the type of fuel
Fine tuning may be required if the chain saw, after changing the type of fuel, performs differently with regard to starting, acceleration, max. speed, etc.
Conditions
•Before any adjustments are made the air filter should be clean and the cylinder cowling fitted. Adjusting the carburettor 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 and H-jets clockwise to the bottom. Now turn the jets one turn anti-clockwise. The carburettor is now set to H = 1 and L = 1.
•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 anti- 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 | | | + 1/4 | | | | | |
| | | | | | |
Try to find the highest idling | | | | | | | | | | |
| | | | | | | | | |
speed, turning the low speed | | | | | | | | | | |
needle L clockwise respectively | | | | | | | | | | |
counter-clockwise. When the | | | | | | | | | | |
| | | | | | | | | |
highest speed has been found, | | | | | | | | | | |
turn the low speed needle L 1/4 | L | | | | | | | | | |
turn counter-clockwise. | | | | | | | | | |
NOTE! If the chain rotates in | | | | | | | | | | |
the idling position, turn the idling speed screw counter-clockwise until the chain stops.
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.
| 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 | |
| closed too much) gives overrevs | |
| and damages the engine. Let | |
| the saw run at full speed for | |
| about 10 seconds. Thereafter, | H |
| turn the high speed needle H 1/4 |
| |
| turn counter-clockwise. | |
Let the saw run again at full speed for about 10 seconds and note the difference of the enginesound. Repeat this procedure with the high speed needle H turned 1/4 turn more counter-clockwise. The saw has now been tested with the following settings: H=±0, H=+1/4, H=+1/2 from basic adjustment. At full speed the engine has produced a different sound for each setting. The high speed needle H is correctly set when the saw ”4-cycles” a little. If the saw ”whist- les” 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 carburettor, contact a qualified servicing dealer who has a revolution counter at his disposal. The maximum speed recommended must not be exceeded.
Correctly adjusted carburettor
A correctly adjusted carburettor means that the saw accelerates without hesitation and the saw 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 accelera- tion. 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.
