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Carburettor Tuning and Adjustment

Before any adjustment is carried out it must be ensured that the engine condition and all other service aspects have been correctly maintained.

Personal Protection Equipment

Use Ear Defenders suitable for chainsaw use.

Tools Required


Make sure the air filter is clean and the cylinder cover is installed before any adjustment is carried out.

Fully screw in (clockwise) both the High and Low jet adjusting screws without using force! Then turn them both anti-clockwise one full turn each (use the raised indicator on the screwdriver).

This basic setting will enable the engine to start.


Should the technician feel that holding the saw with one hand in the high speed adjustment sequence and the circumstances recommended later, is unacceptable they can connect the tachometer to the engine HT lead with accessory lead supplied. They can then hold the saw with both hands when taking speed readings and allow the engine to return to idle during adjustment.

If this connection is required should be made at this stage.

Start Up

Start the engine and allow it to warm up at part throttle for approximately one minute.

Release the throttle trigger and if necessary adjust the throttle stop screw (T) to obtain a reliable tickover. This must be fast enough to prevent the engine stalling but not so fast that the chain will rotate or even attempt to.

Place the saw on a flat surface with the bar and chain pointing away from you making sure that the bar and chain cannot contact any other surface or object…

Low Speed (L) Jet

If the engine casings carry no markings by which to identify this jet the low speed jet is always that nearest the cylinder, irrespective of which side of the engine on which the jet adjusting screws are located.

Always begin the adjustment sequence with this jet screw. With the engine idling, screw the (L) jet clockwise until the engine begins to falter, at this point stop turning the jet and note the position of the lug on the screwdriver. Then turn the jet anti-clockwise until the engine again begins to falter, stop turning and again note the two extremes of travel noted.

Open the throttle quickly to check the acceleration, if this is hesitant turn the jet anti-clockwise incrementally by the width of the lug on the screwdriver at a time until you have smooth acceleration.

High Speed (H) Jet

Ensure that the saw has not move and that the bar and chain remain clear of any unwanted contact. Consult the speed chart to obtain the recommended maximum speed for that model.

Open the throttle fully and holding the tachometer in the vicinity of the spark plug, but without touching the cylinder cover, read off the speed shown.

Then simply turn the (H) jet screw in whichever direction is needed to attain the speed shown on the chart.

Return the engine to tickover and using the tachometer adjust the idling speed as per the chart by means of the throttle stop screw (T). Do not adjust the jet for this purpose.

The speeds listed on the chart are for engines which are fully run-in.

The speed on new or rebuilt engines should be reduced by 600-700 rpm for the first 5 hours of operation.

After this period of operation speeds can be set as per the chart. A general check on the security of all external nuts and screws is also beneficial at this time.

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