Honda CG125 Basic Fault Finding
The Honda CG125 is pretty tough, strong and reliable even with severe
neglect.
The basic fault finding below will fix almost all the common faults your
likely to get with the bike.
Just like the Servicing, its very easy for anyone
without any skills to do and its much cheaper than a mechanic.
A worn out Battery is the most common fault, its also one of the easiest faults to find and fix (see Battery section below in Electrical Faults).
The Honda CG125 has been around since 1976, it has a reputation of being
indestructible and lasts forever no matter what you do to it (not including
crashing it).
I keep hearing this from everyone including motorcycle dealers and mechanics.
They tell me the average Honda CG125 is never serviced, the owners only do
something or take it to a mechanic when they absolutely have to.
They say the majority of faults are often fixed by basic servicing or just
basic simple repairs.
Many UK mechanics keep telling me 80,000 miles is nothing for a Honda CG125,
they say they opened a Honda CG125 engine that had done 80,000 to 100,000
miles and it was perfect inside and had never been opened before.
They say the only reason they normally have to open an engine is if the oil
had not been changed regularly, so they have to clean it out.
They also say the bikes last forever and there are many 25 year old bikes
around (I personally have seen several 1981 to 1986 and newer bikes).
I have not had a Honda CG125 long enough or done enough miles to confirm all
these claims for my self,
I do know over the years the engine has gone through changes and until those
engines have had a chance to do high mileages we only know about old ones.
I assume clutches wear out and are replaced (basic job for a mechanic, does
not require opening the engine).
I personally recommend you service your bike yourself and do not forget about
it like other people do, see servicing page.
When to change the Oil and
Checking the oil level is very
important and should never be neglected.
Serious mechanical
engine fault
Basics
Mechanical faults often affect the fuel to air mixture entering the
combustion chamber (engine).
If the air is restricted you will get a rich mixture,
if the petrol is restricted you will get a lean mixture.
If the mixture is to rich or lean it will ether result in bad engine performance
(and other side effects) or if really bad it will stop the engine from working.
A spark plug colour chart (shows you how the engine has been running, rich /
lean / perfect or other problems).
Look at Normal, Overheated, Carbon Fouled pictures in the link below.
http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
For more Spark Plug information, see Spark Plug
section below.
An explanation of how carburettors work and how they change the mixture at
different throttle positions
http://hondanighthawks.net/carb14.htm
A very useful device that lets you see inside the combustion chamber (engine)
and see the colour of the flame (rich / lean / perfect mixture).
Colortune Review
If the bike has been stored for a long time see Get bike working after storing for months in Servicing page.
Petrol
Petrol ages, if its old petrol it can cause trouble, there are also bad
batches from time to time, try to dilute it with fresh petrol or drain and
replace it.
Some petrol brands and versions have more inbuilt cleaners in than others.
Shell V Power, BP Ultimate, Tesco 99 are more expensive than normal Unleaded
Petrol, but they have extra cleaners in them.
If the engine is able to work, using petrol with extra cleaners in over time
may slowly clean the carburettor and engine.
Over a long time a petrol tank can build up rust, sludge and dirt inside. This
normally settles in the bottom of the tank.
The petrol tap is fed by 2 pipes from the tank, reserve petrol tap position is
a shorter pipe and so feeds from petrol lower down the tank.
So if reserve petrol tap position does not work try the main petrol tap
position.
Only do all the following in the Petrol section below if your sure the fault
is nothing else in this page.
If the bike falls over or if the petrol tank is shaken excessively the rust,
sludge or dirt could float up and then block the main or reserve pipes.
The petrol tap has filters that can become blocked with rust, sludge or dirt
that must be cleaned (only if they become blocked).
Switch petrol tap off.
Unscrew the bottom of the petrol tap and remove the filter.
Clean the filter in petrol, if there are any holes in the filter replace it.
If that fails to work you will need to drain the petrol tank.
To drain the tank remove the rubber petrol pipe, switch the petrol tap to
reserve position and let it drain in to a container.
When the petrol has drained out, get rid of the old petrol since it will be
contaminated from the contents of the petrol tank (it can not be flushed down a
toilet).
Remove the petrol tap from the petrol tank by removing the nut between the tap
and the tank.
Inspect both petrol tap pipes and clean thoroughly in petrol (there probably
are filters on the end of each pipe that need cleaning).
You then need to clean the inside of the petrol tank, petrol is a good
cleaner.
Its probably best to remove the petrol tank,
remove left side panel of bike, unclip right side panel where it clips in to
petrol tank (some bikes do not clip to petrol tank),
unclip petrol tank electrical connection (only bikes equipped with a fuel
gauge have a electrical connection) and un hook wire from the bikes metal frame,
remove seat (see Remove Seat part in
How to find your bikes Tool Kit and Owners Manual section of the
Servicing page),
remove bolt holding tank, remove tank by pulling it towards rear of bike and
up.
If all of the above fails to fix the fault, the carburettor will need to be
cleaned, search the internet or get a Haynes Honda CG125 manual to find out how
to clean it.
A universal motorcycle carburettor cleaning guide will do, you do not need
Honda CG125 carburettor cleaning instructions.
On the internet enter motorcycle carburettor cleaning in to your favourite
search engine.
Cleaning a carburettor is not an extremely difficult job but you have to be
careful, if in doubt find someone who has done it before or ask a mechanic to do
it.
If you need to take carb (carburettor) off,
WARNING do not undo the nuts that hold the carb to intake manifold rubber,
since the carb if over tightened can change shape and will not make a good seal,
so will cause week mixture.
Also as you push carb back you have to use a great deal of force against air box
rubber which will damaged it / split it causing you week mixture.
The way to take the carb off is undo the manifold bolts (8mm head) on the
cylinder head the carb comes out/back in so easy (engine must be cold when this
is done)
Oil
Check the oil level (see Oil page), if its burning oil
the level will drop, you need to see a mechanic if it's substantial.
Make sure you change the oil at the correct mileage or before (see
Oil page).
Spark Plug
Check the spark plug (see Spark Plug page),
look at the colour, this tells you how the engine is running, see
Basics section above for a link to a colour chart.
If its running rich (black sooty deposits = Carbon Fouled) clean the air
filter.
If its running lean check the Exhaust and Silencer (see Exhaust and Silencer
section below), it could also be a fuel starvation (blocked) fault in the
Petrol line or carb.
When choke is on the mixture will be rich.
Its always a good idea to change the spark plug and see if it fixes the fault.
Air filter
Clean it (see Air Filter in
Servicing page), it's always a good idea to clean the filter and see if it
fixes the fault, this would cause the engine to run rich.
If there are holes in the air filter or if the engine is run without an air
filter, the engine would run lean or not at all. Its very bad for the engine to
run without filtered air.
See Basics section above for more information and links
about rich or lean running.
Exhaust and Silencer
If the Exhaust or Silencer has rusted all the way through it will make the
engine run lean or rich (probably lean).
You must replace it, be careful with non Honda parts unless it says it will
not change the mixture of the engine (rich / lean).
If you fit a non Honda part you may have to alter parts inside the carb to get
the mixture correct at all throttle positions.
Make sure any parts are designed for your version of Honda CG125.
See Basics section above for more information and links about rich / lean running and carb
Clutch or Gearbox
Clutch or Gearbox faults can often be due to Clutch
free play, Chain Tension,
Chain Oiling or Idle Speed
(check all of these in the Servicing page).
Clutch Cable
Clutch cables break on any motorcycle, often without warning and no way of
predicting it, see Clutch cable page on how to
service and replace it.
Valve Clearance
Check the valve clearance (see Valve Clearance
page).
If the valve clearance is wrong, some of the problems are, engine performance
/ power may reduce, it can make the engine run rich or lean,
reduce compression, hard to start, if its very wrong valve or engine damage may
occur.
If the valve clearance is to big, you may hear excessive noise from the
valves.
If the valve clearance is to small, you may hear no noise from on of the
valves, this is very bad for the engine.
The noise test should not be relied on, you should only rely on the
Valve Clearance page.
Ignition Timing
If you have a Honda CG125 before 1995 (before S & T models) it could still
have the old Points system.
See Ignition Timing in the
Servicing page.
Just like the Valve Clearance, the Points need to be checked and adjusted.
The Points effect the timing of when the spark plug fires. It also varies the
timing dependant on engine Revs.
If the timing is wrong the power will reduce from the engine.
Front Disc Brake
If the brake looses pressure or becomes spongy, check fluid level, see
Front Disc Brake fluid level
in Brakes page (also part 12 of
Front Disc Brake fluid
changing)
Brake fluid will become spongy over time, replace it at least every 2 years,
see
Front Disc Brake fluid
changing in Brakes page.
If you hear metal grinding against metal when you use the brake see How and when to change the Brake Pads
If the brake seizes on, you need to clean the brake, again its simple, search the internet for information about cleaning (its a single piston calliper).
Air Suction Valve
It's a Secondary Air Induction (SAI) valve system, not an Exhaust Gas
Recirculation (EGR) valve system.
The Air Suction Valve is only fitted in countries that require it to reduce
emissions, the UK and most of Europe did when the front brake went from Drum to
Disc.
The Air suction valve is on the left hand side of the bike just under the
petrol tank. Picture (ignore white arrow)
It has 3 pipes connecting it to the top of the engine, the air filter and the
metal pipe connecting the carb to the engine (intake port).
Air is sucked from the Air Filter in to the Exhaust valve which is on top of the engine, this enables the excess fuel in the exhaust gas to burn in the exhaust.
The Air Suction Valve is actually 2 valves, both valves must be open for air
to flow from air filter to exhaust port.
One opens when there is negative pressure on the exhaust valve at the top of
the engine(so when fumes are sent out the exhaust it sucks air from the air
filter with it)
The other valve is open all the time except when there is negative or low
pressure at the intake port (metal pipe connecting the carb to the engine).
Negative pressure is generated when closing the throttle and decelerating, the
valve must close to prevent after burning.
Low pressure for example is generated at high engine revs, the valve must
close to prevent a loss in performance due to Exhaust Gas Recirculation.
I'm guessing a fault creating Exhaust Gas Recirculation does not sound good if
the exhaust gas ends up in parts not designed for the heat or fumes (air suction
valve).
It looks like you disable the valve by disconnecting the pipe going to the top
of the engine.
You then bung up the pipe and tie it tight to stop air flowing through the
pipe.
The UK MOT still may not check the exhaust emissions of motorcycles (check
first), cars have been checked for many years.
I'm not sure, but its probable that disabling the valve will not improve
engine performance unless the valve is faulty,
people who guess it would may be thinking of Exhaust Gas Recirculation (EGR)
valve system which always reduces engine performance.
Someone told me their Air Suction Valve stuck open, the bike juddered at around 5500 rpm and could not get past 6000 rpm in any gear, see MPH to RPM page.
If you disable the Air Suction Valve I am not sure if it would change the air
mixture (lean or rich), it might at all or some throttle positions?
It could well be that it does not since you have to disable the valve (close
it) when you do an emissions check.
You can find out by checking the spark plug colour, see
Basics section above for more information and links about rich / lean
running and carb
Serious mechanical
engine fault (not easy to do, only for mechanical enthusiasts)
In the unlikely event that your engine has developed a serious fault that can
not be easily or cheaply fixed,
a common solution among Honda CG125 owners is to simply buy a 2nd hand Honda
CG125 engine from a scrap / salvage yard or from ebay.
The idea seems very easy for anyone without any skills to do, unbolt old
engine and disconnect it from everything,
then put 2nd hand engine in and tighten bolts and connect everything.
That would work if its the same exact version of Honda CG125 engine, but often
things slightly change over the years.
You also need to be happy buying a 2nd hand engine and trust that its ok.
The engine is affected by the carburettor, exhaust / silencer and air filter.
Examples,
if the air filter is changed for one that has more resistance the engine will
run rich (less resistance = lean),
if the exhaust / silencer is changed for one that has more or less resistance
it will run rich or lean.
The carburettor is what sets and changes the engine running rich or lean (its
actually called the fuel to air mixture).
The carburettor has to change the settings at different throttle positions
(you need to check the fuel to air mixture is correct at all positions).
See Basics section above for more information and links
about rich / lean running and carb
If you put a engine with a Air Suction Valve in to a bike that does not
support it or the other way round (bike is designed for a Air Suction Valve,
engine does not),
you might be wondering what to do with pipes and connections.
Have a look at the Air Suction Valve section
above to find out what it does and how to disable it. I would seal off any pipes
and connections they connect to.
If you have bought a 2nd hand Honda CG125 and need to work out if the engine
has been changed for a different model version,
check the serial number against one of the websites in
Spare Parts section in the
Links page.
How to buy and fit a new Battery
How to charge a battery and detect if it is worn out
Light Bulbs
If a light bulb fails, you must fix it as soon as possible, you would fail a
police check and a MOT in the UK.
Never ride in the dark without a working headlight.
If the bike is very old the bulbs will be 6 V (volts), if its a modern bike
it will be 12 V (volts), bulb and battery will be marked 6 V or 12 V.
If you accidentally put a 6 V bulb in a 12 V bike the bulb will probably just
burn out immediately (bright flash of light then never works again).
If you accidentally put a 12 V bulb in a 6 V bike the bulbs light output will
be half what it should be.
Headlight, if the dipped headlight blows, use the non dipped headlight
instead, you can point the headlight down to stop blinding other vehicles.
Legally you must still replace the bulb as soon as possible (see
How to replace the Headlight Bulb in the Servicing
page).
Rear Brake light,
if it does not come on when rear brake is applied,
there's an adjustment wire,
it's vertical and has a spring connecting it to the pedal.
Push the brake pedal down and up and find the cable and spring,
there's an adjustment screw in the middle of it.
The indicator bulbs (probably 16w) and the rear light / brake bulb are
probably standard bulbs that all cars and bikes use.
Rear light and brake light are probably combined in to a single dual filament
bulb, one filament for rear light (5w) the other for brake (21w).
Left and Right Turn Indicators, there's a fuse (see
Fuses section below) and a small box
that makes the indicators flash.
Low battery voltage can make the flasher malfunction so check battery first,
see Battery section below. If its a low voltage fault it
should recover with full voltage.
The box could be around the battery, under the seat or be the black box where
the Idle Speed Screw is (see
Idle Screws page), don't touch the idle speed screw.
The box will be a standard flasher, you could probably buy a universal one,
maybe even a car one (if you have a 12 volt system, look at battery to find
out).
But I would see how much a genuine Honda one is.
Fuses, Connectors, Wires
Check the fuses, they are around the battery (behind bikes left side panel),
see if any are blown, there should be spares with them.
Front Disc Brake model has
20A Fuse, this powers the electric engine starter motor and is also the master
fuse.
5A Fuse, this powers the left and right turn indicators.
15A Fuse, this powers everything else including the electric starter motor
button.
If moisture gets in to any electrical connections or wires (usually were the
connectors touch the wire) in the bike, they can corrode (rust),
this increases the resistance for electricity (drops the voltage) and can even
break the connection.
If you have this problem, you need to find it, check any connections you can
find and also look at the wire where it connects to the connector.
If you know how to solder, cutting off the connector and any corroded wire
and soldering instead is much better, it is sealed from moisture and dirt.
Of course if you are bad at soldering, you can create what's known as a dry
joint, this will corrode internally and break the connection.
For people who do not no how to solder, you can do the following.
If the fault is with the wire, you will have to cut off the connector,
cut off all the corroded part of the wire (usually that's only the bit without
plastic around it), take a bit of the plastic off the wire,
then try to reuse the connector or buy a new one.
If the fault is a corroded connector, you can use a normal can of WD40
(available at most motor shops, DIY and even supermarkets).
But only use WD40 if the connector is corroded, WD40 cleans, removes water and
eats corrosion (over time), but leaves a deposit that attracts dirt.
This deposit may help the connection to begin with, but later dirt could brake
the connection,
you can then put more WD40 on and if the corrosion is gone, wipe off the WD40
as much as possible.
On old bikes the electrical wires can become stiff and brittle.
There are several electrical wires that go to the headlight and the front
indicators.
Every time you turn the handlebars these wires are stretched and bent around the
part of the bikes metal frame (chassis) that the handlebars attaches to.
Eventually these wires can brake and even short out, blowing the fuse.
The battery's - (negative = maybe brown or black wire) connector is wired to the
bikes metal frame,
the headlight and front indicator wires are likely to have worn the paint off
the bikes metal frame and so any + wires can short out if there insulation is
worn away.
Some electrical devices on the bike do not have a - (negative wire) instead
they connect to the bikes metal frame to get the - voltage.
When corrosion / rust build up between them it can reduce the voltage or break
the connection.
Battery
Low battery voltage effects all the electrics, including the spark plug.
A test of low voltage is to switch the ignition key on, with the engine off
try the horn, if the tone is much lower than normal, you have low voltage.
You can also do this test with the lights, if they are dimmer than usual with
the engine off, you have low voltage.
If the engine will not start due to low battery voltage and you need it
started soon, try switching off the ignition for a minute or two.
If that fails to work you could try bump starting the motorcycle (may or may not
work).
I have never bump started (push started) a motorcycle but I believe the
technique is the same for all bikes.
Sit on the bike (I do not recommend you try this off the bike, you could drop
it), switch the ignition on, put bike in to 2nd gear, keep clutch pulled in,
move the bike forwards with your feet as fast as possible (best if its down hill
or get some friends to push you),
let the clutch out smoothly and quickly, when engine starts pull in the clutch.
If that fails to work you may have to open the throttle a bit just before or
when you release the clutch, if that fails you may have to try the bike in 3rd
gear.
To get the bike in to 3rd gear you may need the bike to be moving at the time.
Someone made a video of them bump starting a Honda CG125 (looks like electric
start only version with low battery voltage)
Push Start Honda CG125 Video
A more detailed video of how to bump start a different bike
Motorcycle Bump Start Video
An electric start Honda CG125 needs a massive amount of power (voltage and
current) to start the engine (battery needs to be healthy and fully charged or
nearly).
A failing battery might seem to have enough voltage but when the electric start
is used the voltage can drop significantly resulting in the engine not firing
up.
The electric start may turn the engine over (might be slower than normal), but
not have enough voltage left to ignite the petrol.
It may not even have enough voltage to turn the engine over and you only hear a
click instead.
If you have a kick-start as well, try it since it needs far less power than an
electric start.
As soon as you take your finger off the electric start button the battery may
return to a good voltage.
The Front Disc brake Honda CG125 automatically cuts off the front headlight
briefly when the electric start is used (this is deliberate design and not a
fault).
Some Honda CG125 electric starter motors have failed (they just go click and do
not turn over the engine even though battery is fine),
I believe they fail due to black dust building up inside, all you have to do is
remove the starter motor and clean its insides.
The starter motor is the round cylinder underneath the choke lever, someone made
a video
Part 1
Part 2
Part 3
Some people have got the starter motor going by hitting it with a hammer
instead.
There is also the possibility that the engine just needs to turn over once or
twice (with ignition off, put bike in to 2nd gear and turn wheel by hand).
There are several reasons for low battery voltage.
1. It's simply worn out, this is by far the most likely.
2. If it's a maintenance battery, see Battery
in the Servicing page.
3. You have left it for months and so it has gone flat (all bike batteries
loose charge over time so charge it).
4. You have been doing loads of very short journeys and it has not been able
to recharge enough (not so likely if you use a kickstart),
5. The engines battery charger has stopped working or the fuse / wire
connecting it to the battery has failed.
6. You have an alarm fitted and it has drained the battery.
7. You have left the lights on (if your model has that ability).
Testing the motorcycles battery charger is probably easiest by simply
replacing the battery, if the new battery suffers low voltage with use,
it must be the motorcycles battery charger.
You can test the battery with an automatic battery charger, see the section below called How to charge a battery and detect if it is worn out.
You can test the battery, but you could also just replace it.
If you have a voltage meter you can do some basic tests.
When the engine has been off for at least 1-2 hours with ignition key turned
off,
100% Charged 12.60 to 12.8v
75% Charged 12.4v
50% Charged 12.1v
25% Charged 11.9v
0% Charged less than 11.8v
When the engine has been off for at least 1-2 hours,
Switch ignition key on and switch headlight on (engine must not be running, some
Honda CG125 headlights only work with engine running),
you need at least 11.5v on a 12v battery or 5.75v on a 6v battery.
When the engine is running the bikes inbuilt battery charger should raise the
voltage well above 13v especially when the engine revs are well above idling.
You need at least 14.2v to recharge a 12v battery. A failing battery can drag
the bikes inbuilt battery chargers voltage down.
How to buy and fit a
new Battery
The front disc brake model Honda CG125 is supplied with a Yuasa maintenance
free battery.
It's probably for the electric starter motor, since it has twice the current
to start the engine, recovers and recharges faster than a conventional
maintenance battery.
It also self discharges nearly 3 times slower than a maintenance battery (so
bike can be stood for longer without battery needing to be charged).
The downside of the maintenance free battery is it costs 3 times more than a
maintenance battery but Yuasa claims it will last 3 times longer so costs the
same.
I am not sure if the older Honda CG125 electric start bikes were supplied
with a Yuasa maintenance free battery or not (read the paragraph above about
it).
I have a strong feeling they were since electric start needs a massive amount
of current from the battery to start the engine.
A Yuasa conventional maintenance battery would need to be twice the
size(capacity = eg. 8 Ah) to deliver the same current as a maintenance free
battery(eg. 4 Ah)
I am pretty sure the kickstart only Honda CG125 have always had the maintenance type battery since you need far less current to start the bike.
Some maintenance free batteries need a bike designed to work with them, other makes of maintenance free batteries may have a different amount of current output.
When buying a new battery, you need the details of the old one.
If you find a model number on the battery, you may be able to buy the same
battery or find a conversion chart for other makes.
Front disc brake model has a Yuasa YTX5L-BS (12V 4Ah maintenance free)
Front drum brake model with electric start probably has a Yuasa YTX5L-BS (12V
4Ah maintenance free)
Front drum brake model with kickstart only and 12 Volts probably has a Yuasa
YB2.5L-C (12V 2.5Ah extra power maintenance)
Front drum brake model with kickstart only and 6 Volts probably has a Yuasa
6N6-3B (6V 6Ah conventional maintenance)
The voltage should be on the battery and on every light bulb, it will be 12V or 6V. A 12V battery has 6 compartments (6 filling holes), 6V only has 3.
If the model number is no good you will have to find the following on the
battery.
The most important thing is the voltage and capacity (front disc brake model
is 12V and 4Ah), do not change the voltage or capacity.
There have been many different versions of Honda CG125 over the years and the
voltage and capacity required has changed several times.
A common mistake is to fit a higher capacity battery than original, this can
overload the bikes electrical system and cause many faults.
The next thing you need is the physical size of the battery, height, width,
depth to make sure it fits.
Then you need to know which way round the + and - connections are.
If its a maintenance battery, you need to make sure the plastic breather tube
is in the correct place or its supplied with a longer one that will fit.
Maintenance Free batteries have no plastic breather tubes since they are
sealed.
Of course the battery compartment of the bike might allow a different size of
battery and plastic breather tube (if the battery has one).
There are different battery terminals requiring different connectors (some
times a new battery comes with new connectors to put on the bikes wires).
A new battery will come with an instruction leaflet, if you pour the acid in
to the battery read it,
it will tell you to stand the battery for at least 30 minutes after pouring
the acid in (before charging).
It may tell you to tap the battery to get air bubbles out and pour more acid
in if the level drops on maintenance type batteries.
A new battery is semi charged when assembled (probably 80% charged),
for maximum performance and life it should be fully charged with a charger
before putting it in the bike (see
How to charge a battery and detect its worn out below).
A shop or you can charge it, but it takes time.
After charging for the first time, if it's a maintenance battery the fluid
levels must be checked (ideally pour acid in if needed), see
Battery in the Servicing page.
When fitting a maintenance battery, you must connect the plastic breather
tube, it needs to point down and away from the bike,
this is usually in the middle of the bike, just in front of the rear wheel.
This tube may have corrosive gasses and liquids pouring out, so do not let it
point at anything other than the ground.
The battery terminals and any exposed (bare metal, not plastic) metal wires
connecting to them,
need to be protected from the corrosive gasses from the battery, this might
not apply with maintenance free batteries,
but it definitely does for maintenance batteries.
I put any type of grease over them to protect them, you can buy special grease
for this, but there's no need.
Make sure you do not get grease between the battery terminals and the
connectors, unless the grease is designed to allow voltage to pass through it.
How to charge a
battery and detect if it is worn out
Do not use a non automatic battery charger unless its designed for motorcycle
use, else it will charge the battery far to fast and damage it.
Maintenance free (sealed) batteries can easily be damaged if overcharged so an
automatic (smart) battery charger is recommended because it will not overcharge.
If you have a battery charger that's designed only for motorcycle use (not
car and bike), you can skip this paragraph.
You may be able to use a car automatic battery charger, it may even say
suitable for motorcycles or has a motorcycle switch.
If an automatic(smart) battery charger charges the battery with a constant
voltage during the entire charging sequence, you can use it on any motorcycle
battery.
Do not confuse it with a charger that uses both constant voltage and constant
current in the charge sequence.
Constant voltage means the battery controls the current so it does not matter
how small the battery is (motorcycles are very small), it will not damage it.
If the battery charger uses constant current in any of the charging sequence
you need to be very careful to make sure it does not damage a motorcycle
battery.
A motorcycle battery is identical to a car battery except for its capacity
(size), cars might be 35 to 70 Ah and motorcycles 2.5 to 25 Ah.
Some car battery chargers claim to also work with motorbikes with a 2 A charge
current, many (including motorcycle only chargers) are 0.8 or 0.6 A (600 mA).
Ideal charge current is 10% of its capacity. The Honda CG125 battery is one of
the smallest motorcycle batteries made, since its engine size is small.
Honda CG125 front disc brake model battery is 4 Ah so it ideally wants 0.4 A
charge (your very unlikely to find a charger with such a low output).
Often you can not find out if an automatic battery charger has constant
current in the charging sequence so my advice in these cases is to,
check the charger outputs or has a switch to output 0.6 or 0.8 A (600 or 800
mA) or it claims to work with your battery capacity (size).
To charge a battery, you must disconnect at least one of the battery
terminals from the bike.
This is to stop the battery charger damaging the bike's electrical system.
The negative battery terminal is often hooked up to the bikes metal frame, so
its best to remove the positive battery terminal (Red wire),
since if the battery charger accidentally touches the metal frame,
it would send the battery charger voltage through the bikes electrical system
if only the negative terminal was disconnect.
An automatic battery charger will tell you when the battery is fully charged, a faulty or worn out battery will probably never reach fully charged.
If you have a very old Honda CG125, your battery may be 6 V (volts) instead
of the normal 12 V,
if its 6 V you need a battery charger which is or can switch to 6 V.
If you have a 6 V battery, all of the bikes electrical system and everything
that connects to it will be 6 V,
do not change it for a 12 V battery since it would destroy everything.
All batteries will have a label on them stating if they are 6 V or 12 V, if
the label has worn off, all the light bulbs will also state if they are 12 V or
6 V.
6 V maintenance batteries have only 3 compartments to top up with water
(distilled), 12 V maintenance batteries have 6.
