Taper Needle; Size Of The Throttle Valve's Bevelled Edge; Main Jet; Carburettor Setting - Husqvarna CR 125 2011 Workshop Manual

Workshop Manual Ed. 06-2011
ENGINE OVERHAUL
CR 125 2011 - WR 125 2011

Taper needle

The taper needle influences the air-fuel mixture from the small and medium
openings of the throttle valve. Size 60, at the end of the code found on the part,
indicates that the external diameter is 2.60 mm. The smaller the diameter of the
needle, the more the mixture is enriched.

Size of the throttle valve's bevelled edge

The size of the throttle valve's bevelled edge influences the air-fuel ratio at
openings of the valve from 1/8 to 1/2 and especially between 1/8 and 1/4.
If the valve's bevelled edge increases, the resistance to air flow decreases,
leading to an increase in the air intake with a corresponding impoverishment
of the mixture. Conversely, if the valve's bevelled edge decreases the mixture
is enriched.

Main jet

The main jet regulates the quantity of fuel that must be supplied to its circuit
and is marked by an identification number that indicates its size. The higher
this number is, the larger the diameter of the jet, leading to a corresponding
mixture enrichment.

Carburettor setting

The concentration of oxygen in the air changes in relation to temperature, al-
titude and humidity; these elements therefore influence the setting of the car-
burettor. Since the effects of humidity on oxygen concentration are negligible,
the two elements that must be taken into consideration are temperature and
altitude. Therefore, the quantity of fuel to be mixed with air must vary accord-
ing to specific environmental conditions, keeping in mind that an increase in
the oxygen concentration in the air causes the impoverishment of the mixture,
while a decrease leads to its enrichment.

How to evaluate the mixture

For a correct setting, it is necessary to evaluate correctly the air-fuel mixture
supplied by the carburettor; below is a list of guidelines for the evaluation.
The symptoms of a too poor mixture are the following:
- The engine overheats;
- Acceleration is faulty;
- The engine tends to knock and makes an irregular noise;
- The spark plug tip is white or grey;
- The engine does not develop power.
The symptoms of a too rich mixture are the following:
- The engine behaves like a 4 stroke;
- The engine misfires at low rpm;
- Deposits on the spark plug;
- Acceleration is faulty;
- The exhaust releases excessive emissions.
G.22