Beta RR 4T-400 Workshop Manual page 47

Carburettor - Idle speed adjustment
The adjustment of the idle speed strongly affects engine start-
ing, i.e. an engine whose idle speed is properly adjusted is eas-
ier to start than an improperly tuned engine.
The idle speed is adjusted by means of adjusting roller 1 and
mixture adjusting screw 2. The adjusting roller alters the base
position of the throttle valve; the mixture adjusting screw adjusts
the idle speed mixture, which comes to the engine through the
idle speed system. Turning the screw clockwise decreases the
quantity of fuel (lean mixture); turning it anticlockwise increases
the quantity of fuel (rich mixture).
To properly adjust the idle speed, follow these steps:
– Turn in mixture adjusting screw 2 until it stops, then turn it to
obtain the basic adjustment prescribed by BETAMOTOR (see
engine specifications in Chapter 3).
– Warm up the engine.
– Using adjusting roller 1, adjust the standard idle speed (1400
- 1500 rpm).
– Slowly turn mixture adjusting screw 2 clockwise until the idle
speed begins to decrease. Memorize this position. Now slow-
ly turn the mixture adjusting screw anticlockwise until the en-
gine speed starts to decrease again. Choose the point be-
tween these two positions where the idle speed is higher.
Should the engine speed increase considerably, reduce it to
the standard level and repeat the above procedure.
NOTE: Failure to successfully complete the above procedure
may be due to an idling jet of unsuitable size.
a)If the mixture adjusting screw is turned until it stops and the
idle speed does not change, fit a smaller idling jet.
b)If the engine stalls while the mixture adjusting screw is still two
turns open, fit a larger idling jet.
Obviously, once the jet has been replaced, the adjusting proce-
dure will have to be restarted from the beginning.
– Now use the adjusting roller to obtain the desired idle speed.
– The idle speed needs to be adjusted again in case of marked
changes in the outside temperature and the riding altitude.
Basic information about carburettor wear
The throttle valve, the jet needle and the needle jet are subject
to heavy wear and tear due to engine vibrations.
This could result in carburettor malfunctions (e.g. a richer mix-
ture).
4 - Maintenance
Release 01 Date 09/2007
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