1. GENERAL INFORMATION 1.1 Original calibration

Each machine's carburation is factory-adjusted, in controlled environmental conditions, comparable to those found at sea level. This calibration allows for optimal carburation, ensuring top performances and simultaneously reducing pollutant emissions.

1.2 Environmental variables

An endothermic engine's performance varies according to the atmospheric pressure and is therefore sensitive to variations in altitude.

Performance decreases normally around 10% for each 1000 metres of altitude above sea level. This is indicated by a reduction in the maximum speed, which causes an increase in fuel consumption.

1.3 When to calibrate carburation

Normally, carburation must be calibrated after the carburettor has been replaced or serviced and when environmental conditions of use deviate significantly from factory conditions.

1.4 Necessary equipment

Carburation must be calibrated by a qualified Service Centre, using an electronic tachometer. Special screwdrivers suited to the various adjusting screws are necessary, whose shape is indicated in the summary charts at the end of this document.

1.5 Operator precautions

Carburation must be calibrated in a suitable place, and requires proper devices for suction and fume removal. The operator must wear suitable clothing and use the personal protective equipment provided for by the laws in force on the matter of safeguarding health and preventing accidents at the workplace.

2. THE CARBURETTOR

2.1 The carburettor's operating principle

Air, under the effect of a vacuum created by the piston, pulls fuel through the high «H» jet above the valve connected to the throttle.

2.2 Adjusting screws and effects

These carburettors are equipped with:

- «H» screw for the high jet (if provided): tightening (clockwise), a weaker air/fuel mixture is obtained with an increase in engine speed;

loosening (anticlockwise), a richer air/fuel mixture is obtained with a reduction in engine speed;

- valve adjusting «T» screw:

tightening (clockwise), the valve is opened and the minimum speed is increased;

loosening (anticlockwise), the valve is closed and the minimum speed is reduced. Adjustments should be made one at a time, making sure that the desired effects are obtained.

3. CALIBRATION PROCEDURE

3.1 Machine presetting

Before calibrating:

- empty the fuel tank and refill it with petrol/oil mixture in the proportions indicated in the machine Instruction Manual;

- make sure that the air filter is clean and properly fitted. The machine must be set up with:

- cutting line head mounted, with the line cut to the maximum allowed length;

- guards mounted.

3.2 Calibration phases

1. Start up the engine following the indications in the Instruction Manual, and accelerate for at least 1 minute continuously to warm it up. If the engine will not run for a long enough time, you must reset the adjustments and carry out pre-calibration, as indicated at point 3.3.

2. Release the throttle to reduce the engine to minimum.

3. Check that the minimum rotation speed corresponds to the value indicated in the chart (Engine RPM setting) for each machine model.

4. If the values are different, use the «T» screw to obtain the correct minimum speed.

5. Accelerate completely and check that the maximum rotation speed corresponds to the value indicated in the chart (Engine RPM setting) for each machine model.

6. If the values are different, use the «H» screw in both directions (only on carburettors that are equipped with them) to obtain the correct maximum speed.

3.3 Carburation pre-calibration

This operation is necessary when the machine is not properly tuned and is not able to run long enough to carry out the checks indicated at point 3.2.

1. Tighten the «T» screw 2 complete turns from the beginning of the contact with the valve lever.

2. Tighten the «H» screw (if provided) completely without forcing it, then loosen it (anticlockwise) with 2 complete turns.

3.4 Results and check

When calibration is completed, accelerate twice completely, alternating by allowing the engine to return to minimum, to check acceleration progression and if minimum and maximum values are maintained.

The minimum engine speed must be such as to not cause the cutting device to move when the throttle and choke are not operated.