1. GENERAL INFORMATION 1.1 Original calibration

The carburation of each machine is regulated in the factory, in controlled environmental conditions, comparable to those found at sea level. This calibration allows optimal carburation, such as to ensure the maximum level of performance and, at the same time, reduce polluting emissions.

1.2 Environmental variables

The efficiency of an internal combustion engine varies in relation to atmospheric pressure and is therefore sensitive to changes in altitude.

The drop in efficiency is normally around 10% for every 1000 meters above sea level; this is evidenced by a reduction in the maximum speed, which is reflected in higher fuel consumption.

1.3 When to perform the carburation calibration

Normally, the carburetion calibration must be performed in case of replacement or revision of the carburettor and if the environmental conditions of use deviate significantly from those of the Factory.

1.4 Equipment needed

The carburetion calibration must be carried out at a qualified Center, with the use of an electronic tachometer; screwdrivers suitable for the various adjustment screws are also needed, the shape of which is indicated in the summary tables that complete this document.

1.5 Precautions for the operator

The carburetion calibration must be performed in a suitable place, equipped with adequate devices for the aspiration and evacuation of the fumes; the operator must wear appropriate clothing and make use of the individual protective devices provided for by the current regulations regarding the protection of health and the prevention of accidents at work

2. THE CARBURETOR

2.1 Type of carburettor and operating principle

The operating principle of the carburettor mounted on these machines is schematically shown in the figure.

The air, under the effect of the depression created by the piston, draws fuel through the jets of the minimum "L" and the maximum "H" located respectively downstream and upstream of the throttle valve.

With the engine idling (and therefore with the accelerator released), the throttle is almost completely closed and the fuel mainly comes from the "L" jet.

Accelerating, the throttle opens and the predominant supply of fuel takes place through the "H" jet.

2.2 Adjusting screws and effects

These carburettors include:

- screw «L» of the idle jet:

screwing (clockwise), the passage of the air / fuel mixture is closed and the

idle speed;

unscrewing (anti-clockwise), the passage of the air / fuel mixture opens and the engine idle speed is increased.

- screw «H» of the maximum jet:

screwing (clockwise), a leaner air / fuel mixture is obtained with an increase of

engine speed;

unscrewing (anticlockwise), a greasy air / fuel mixture is obtained with a reduction in engine speed.

- throttle adjusting screw «T»:

screwing (clockwise), the throttle opens and increases the idle speed; unscrewing (anticlockwise), the butterfly is closed and the engine speed is reduced to the minimum.

It is a good rule to make one adjustment at a time, checking that the effects correspond to what is desired.

3. CALIBRATION PROCEDURE

3.1 Preparing the machine

Before carrying out the calibration it is necessary to:

- empty the fuel tank and refuel with petrol / oil mixture in the ratio indicated in the Instruction Manual of the machine;

- make sure that the air filter is clean and correctly assembled. The machine must be set up:

- with the chain assembled and tensioned correctly, taking all precautions to avoid accidents if the chain starts moving;

- resting on a bench in a horizontal position.

3.2 Carburation calibration

1. Start the engine as indicated in the Instruction Manual, and keep it accelerated for at least 1 minute to warm it up. If the engine does not run for a sufficient time, a reset of the settings and a pre-calibration must be carried out, as indicated in point 3.3.

2. Release the accelerator to bring the engine to idle.

3. Tighten screw «L» until the engine tends to stop, at an indefinite speed.

4. Act appropriately on the screw «T» in both directions, until reaching the "TOP" rotation speed indicated in the table (Engine RPM setting) for each machine model.

5. Unscrew the screw «L» (anticlockwise) until reaching the minimum rotation speed corresponding to the value indicated in the table (Engine RPM setting) for each machine model, obtaining the result of keeping the engine running, with the chain stops.

6. Accelerate fully and check that the maximum rotation speed corresponds to the value indicated in the table (Engine RPM setting) for each machine model.

7. If different values ​​are found, it is necessary to act appropriately on the screw «H» in both directions, until the correct maximum speed is obtained.

8. Carry out a further check of the idle speed and, if necessary, act appropriately on the screw «T» in both directions, until reaching the value indicated in the table (Engine RPM setting) for each machine model.

3.3 Carburetion pre-calibration

This operation is necessary when the machine is totally scarpened and therefore unable to remain in motion for the time sufficient to carry out the checks indicated in point 3.2.

1. Fully tighten the screws «L» and «H» without forcing them, then unscrew them (anticlockwise) by 2 complete turns.

2. Tighten screw "T" 2 full turns from the beginning of contact with the throttle lever.

3.4 Result and verification

Once the calibration has been carried out, perform two accelerations at the bottom interspersed with a return to the minimum, to check the acceleration progression and the maintenance of the minimum and maximum values.

The engine speed at idle must be such as not to cause any movement of the chain when the accelerator and the starter are not activated.