Some of the motorcycle owners always ignore small parts when doing the maintenance for their motorcy

1. Some of the motorcycle owners always ignore small parts when doing the maintenance for
their motorcycle, and then it will leave some problems or quality issues for the motorcycle
accessories even after repaired and affect the service life.
Here we will discuss about some problem which is easy to be ignored in the process of
motorcycle maintenance, like circuit, oil, gas or mechanical parts.
1. Minimum ignition speed
In general, magneto ignition system has minimum ignition speed and it can ensure that the
ignition system can realize high voltage ignition at low engine speed. However, most
repairman will usually remove the spark plug on the fault engine and do the arcing tests on
high-pressure damping cap when there is a ignition failure. These methods are simple and
easy and have been widely adopted by them. But some engine failure like difficult to start, is
due to ignition coil and the electronic igniter with a high ignition speed.
Such as Honda CH125 water-cooled scooter, its minimum ignition speed is 300 r/min. If the
minimum ignition performance reduces, the minimum ignition speed increase, and it
sometimes even need to reach more than 400 r/min to ignite. If the repairman still use simple
arcing tests as above, then they may be fooled by some false appearance and even mislead.
This is because there is no compression resistance in the cylinder when the piston runs up
and down without spark plug in the engine; the start speed is above 400 r/min, which is much
higher than with speed with the spark plug. At surface, the spark plug does have a spark at this
moment, but after putting it on engine and then apply electric start or pedal starts, then, there
is certain pressure inside the cylinder and the running resistance will increase, start speed will
be only about 300 r/min. If the battery voltage is low, then the start speed is even lower, which
can’t meet the minimum ignition speed, of course, the motorcycle will not start.
Therefore, when using the spark plug or ignition coil to ignite, make sure to install a spark plug
in the engine, or it is even better to use electronic tachometer to measure start speed. If using
the old battery around 12 V, the start speed is around 300 r/min to 350 r/min, the spark is weak,
while using the new battery above 13.5 V, the start speed is more than 400 r/min, the spark is
blue and white, then we can get a preliminary conclusion: the minimum ignition speed is too
high. Then, you need to test the performance of each electric equipment of ignition system,
and replace the ignition coil and electronic igniter for contrast test, which can eliminate the
failure.

2. 2. The ignition triggers gap or the air gap
The ignition system of motorcycle engine generally adopts the flywheel rotor type, while
magnet and flywheel are united into one and form as a part of the engine flywheel, and
permanent magnets rotate together with the flywheel and form a magnetic field, then there will
be induced current in the fixed coil, at the same time play a role of mechanical energy storage
and release. Four-stroke engine use non-contact ignition system, the trigger coil of magneto is
at the external of the flywheel rotor, where there is a permanent magnets, with the rotor
rotating, trigger coil will induce pulse current and provide trigger signal to electronic ignition
device (CDI).
In order to ensure that the ignition system has a strong ignition trigger signal, while it will not
interfere trigger poles and flywheel rotor, so there is trigger gap around 0.40 mm to 0.80 mm
between the trigger pole and the flywheel rotor. In general, the gap can be adjusted by the
mounting hole or oval hole on trigger pole. Due to the error at manufacturing, or reassemble
after repair, or trigger pole wear and tear, the ignition trigger gap may get bigger, thus affecting
engine ignition performance in different degrees. Besides, there is also air gap between
cylindrical stator and flywheel magnetic, under normal circumstances, unilateral air gap should
be no greater than 0.75 mm, in order to ensure the magneto ignition and charging system work
normally.

3. For a 125 type motorcycle, driving more than 43000 kilometers, after the stator component
was changed for the magneto fault and then electric start can’t work while the pedal start is
normal. Then, repairman will check both static and dynamic of battery voltage, which turns to
be normal, overrunning clutch, start circuit and relay are also normal, then check
the starter circuit, carbon brush and so on, they are all normal. Remove the spark plug, put it
on the high-pressure damping cap and do electric start check, the spark is dark red, and after
changing a spark plug, electric start is still not working. Then you need to replace the stator coil,
and remove the ventilation cover, check the trigger gap between flywheel and trigger pole,
there are unexpectedly about 2.0 mm. Realigns the trigger to standard 0.50 mm, reinstall the
parts, then electric start can work successful now.
Another 125 scooter, due to loss of excitation with the magneto flywheel rotor, vehicle cannot
be started even after replacing new parts. After several check, the problem turns to be the
flywheel rotor wall, whose diameter is too large and exceeds the specified value between the
stator cylindrical. Replace the magneto flywheel, check the gap between stator cylinder and
the flywheel rotor wall, make sure it is less than 0.50 mm, assemble the dismantled parts, start
the engine, then the failure is solved.
You can be seen from the examples above, repairman didn’t adjust the trigger gap according
to the rule when changing the stator component, the ignition trigger gap will be too large. When
applying the pedal start, because recoil inertia is big, it can barely achieve start speed; and
when electric start, because starter speed is relatively low, the large gap will reduce the pulse
signal, the spark is not strong enough to start. And the other motorcycle can’t be started
because the air gap is too big between cylindrical stator and the flywheel rotor magnetic
cylinder wall, which will seriously affect the ignition performance of magneto.