Honda CB160 Shop Manual page 91

5. 3 IGNITION CIRCUIT
87
E. Spark advancer
The angle advancing mechanism automatically acce-
lerates ignition timing in accordance to an increase
of engine rotation. This is performed by a device
fixed by a screw and adjusted by a wire. In the
latter case, adjustment is performed by changing the
position of the breaker arm. When the positions of
the cam and breaker arm are changed, adjustment is
obtained That is when the breaker arm is fixed, the
cam moves correspondingly to the number of rotations.
In the CB 125 and CB
l
60 spark, the cam is moved
by utilizing centrifugal force. (Refer to Fig, 5. 25)
As shown in Fig. 5. 26, the spark advance mecha-
nism is fixed by a spring at a position of
O
angle
advance (5° prior to top dead center]. However,
corresponding to rotation, the weight opens outward
resisting the tension of the spring by centrifugal force,
thereby rotating the cam. (The rotating direction ac-
celerated by the spark time.I
The dotted line in Fig. 5. 26 illustrates the full
advanced position. The advance angle of the spark
advance mechanism opens at l 600 r.p.m. and is re-
leased at approximately 4200 r.p.m. The angle ad-
vanced is from 5° to 45°. (Refer to Fig. 5. 26)
In Model CB 125 and CB
l
60, the spark advance
mechanism is included in the camshaft. Only the
paint cam is exposed at the paint section which makes
visual inspection of the advance mechanism difficult.
However, it is necessary to inspect and insure correct
operation of the weight by turning the paint cam
rotor.
Angle advance starts ...... crank r.p.m •
. . . .. • l 600 r.p.m.
Angle advance ends ...... crank r.p.m.
...... 4200 r.p.m.
Advanced angle ..... .40°
l. Maintenance and replacement
In the spark advance mechanism, the centrifugal
piece, spring hook hole, and the coupling section of
the cam are worn after prolonged use, causing in-
creased play. These are indicated in a totally com-
bir,~d status, an advance characteristic. The spark
advance mechanism should be replaced if the following
is noted:
*
A
range deviation.
*
Generation of noise.
*
Rough advance curve.
Fig. 5. 25 Spark advancer
RECESSED SEAT
FOR
ROTATION
MEASUREMENT
5° ADVANCE ANGLE
45°ADVANCE ANGLE
Fig. 5. 26 Graph of spark advancer
CHARACTERISTIC RANGE OF
ADVANCE ANGLE
._______,_~ I I
O
1,000 2,000 3,000 4, ,000 6,000 7,000 8,000 9,000 10.000
1.100 3,900 MOO CRANKSHAFT SPEED (R.P.M.)
Fig.
5.
27 Graph of advanced angle of spark advancer