Beta RR 4T-400 Workshop Manual page 149

Carburettor - Idle speed adjustment
The adjustment of the idle speed strongly affects engine starting.
In other words, an engine whose idle speed is properly adjusted
is easier 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 is used to alter the basic position of
the throttle valve; the mixture adjusting screw is used to adjust the
idle speed mixture, which comes to the engine through the idle
speed system. Turning the screw clockwise decreases the quan-
tity of fuel (lean mixture); turning it anticlockwise increases the
quantity of fuel (rich mixture).
TO PROPERLY ADJUST THE IDLE SPEED, FOLLOW THESE
STEPS:
1 Screw in mixture adjusting screw 2 until it stops and then screw
it out until the basic adjustment specified by Betamotor is ob-
tained (see Chapter 3 Tightening torques - Specifications - Rec-
ommended products).
2 Warm up the engine.
3 Using adjusting roller 1, adjust the standard idle speed (1400 -
1500 rpm).
4 Slowly turn mixture adjusting screw 2 clockwise until the idle
speed begins to lower. Memorize this position and then slowly
turn the mixture adjusting screw anticlockwise until the idle
speed begins to lower again. Choose the point between the two
settings where the idle speed is highest. Should the engine
speed increase excessively, decrease the speed to the stan-
dard level and go through step 4 again. Anybody using the ve-
hicle intensively for sporting purposes should choose a leaner
mixture by approximately 1/4 of a turn (clockwise) relative to this
ideal value. This is because, in these conditions, the engine
heats more than in standard use.
NOTE: If the above procedure should prove unsuccessful, the
problem 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, a smaller idling jet is needed.
b) If the engine stalls while the mixture adjusting screws is still
open by two turns, a larger idling jet is required.
It goes without saying that, after replacing the jet, the adjust-
ment will have to be restarted from the beginning.
5 Turn the adjusting roller until the desired engine speed is ob-
tained.
6 The idle speed will have to be readjusted 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 nozzle are subject to
heavy wear and tear caused by engine vibration. This may result
in carburettor malfunctions (e.g. enrichment of the mixture). The
above-mentioned parts should consequently be replaced after
200 hours.
Mixture adjusting screw
The mixture adjusting screw is difficult to reach. For this reason a
special tool is provided to facilitate the task. Place the special tool
on mixture adjusting screw 2 on the lower side of the carburettor.
Slightly press the tool upwards and turn adjusting roller 3 until the
tool snaps into the slot of the mixture adjusting screw. Now it is
possible to perform the adjustment. The roller has reference
marks for the turns.
Checking the float level
Remove the carburettor and the float chamber. Tilt the carburettor
so that the float rests on the float needle valve without crushing it.
In this position the float edge should be parallel with the sealing
surface of the carburettor float chamber (see figure). If the float
level differs from the nominal value, check the float needle valve
and if necessary replace it. If the needle valve is in working order,
the float level can be adjusted by bending float lever 4. Fit the car-
burettor float chamber and the carburettor and then adjust the idle
speed.
7 - Carburettor
Release 01 Date 09/2007
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