Motorcycle Owners Club

Honda CG125 but also some universal motorcycle information

Honda CG125 Servicing

The bike has been designed to be very easy to service; there is no need to pay a mechanic.

If you insist on paying a mechanic, find out what their hourly labour charge is, then insist on watching them work.
This means you will know they have carried out the work, the real time it takes and how to do the work yourself next time.

The Owner's Manual states you should use a torque wrench,
there's no need for one unless your hands are very insensitive.

If you bought a 2nd hand bike, the chances are the previous owners have not bothered to service the bike.
So I would advise doing everything in the Servicing pages and this page as soon as possible.

How to find your bikes Tool Kit and Owners Manual

All motorbikes when new come with an Owner's Manual and a basic tool kit for the bike.
These are normally stored in special compartments in the bike.
It's not uncommon for the owner to remove and store the Owner's Manual away from the bike,
and fail to return it to the bike or pass it on to the new owner when they sell the bike.
I would hope they do not do the same with the tool kit;
it should always be left in the bike when travelling in case of breakdown.

Trying to find these special compartments can be tricky since they are small
and often change from model to model of Honda CG125.
The tool kit for example is around 14 cm long, 7 cm wide and 3 cm high on the front disc brake model.
It has the basic tools needed for the bike, like the rear suspension adjustment C spanner,
spark plug tool and several other spanners and screwdrivers.
On the front disc brake model, the special compartment is behind the left hand side panel, beneath the battery.
But on other models it could be under the seat or even in the tail of the bike or just strapped to the battery.
There's a small chance it could be behind the right hand side panel, but all that space is normally taken up by the air filter.

How to remove the seat depends on the model.
It's usually held on by 2 screws or 2 nuts and bolts at one end of the seat (one on each side).
They are usually underneath the back of the seat pointing horizontally (look underneath the mudguard),
but some models are at the front (you need to remove both side panels to get to them).

There's even a possibility that instead of screws or bolts,
it has 2 latches at the back, pull them towards the back of the bike to release,
there could be a wire from the seat locked to the helmet lock to stop people stealing the seat.

The other end of the seat is normally held in place by a piece of the seat slotting in to a hole.

If there's a storage compartment in the tail of the bike,
you will need to remove the seat and unbolt and remove the grab rail, unbolt the tail from the bike and remove.

The Owner's Manual is stored in a special compartment beneath the right hand side panel on the front disc brake model,
but could also be in the same places as the tool kit mentioned above in other models.


My website has been designed so you do not need any manuals,
but if you have any of the following, I would use them as well as my website
(always look at my website as well for any subject since it may or may not have more information and be easier to understand).

You can buy the Haynes Honda CG125 Owner's Workshop Manual;
this can probably replace the Honda CG125 Owner's Manual.
It also tells you how to service and repair the bike.
Make sure it supports your model year, you will also find that it tells you everything about the oldest model it supports,
then in the back of the book it tells you the changes in the instructions for newer models.

You can also buy the official Honda CG125 Workshop Manual for your model of Honda CG125.
You can probably get it from your local Honda dealer,
but this manual is designed for experienced mechanics, so it probably will not tell you how to do very universal basic things.


It's behind the left hand side panel, if not it must be behind the right hand side panel (very unlikely).

If you have a maintenance free battery, you do not and must not try to check or change the liquid levels below;
a maintenance free battery should have maintenance free printed on it.
The original battery in the front disc brake model is maintenance free (all electric start Honda CG125 could be the same).

If you have a maintenance type battery (will not have maintenance free printed on it),
you need to keep an eye on the liquid levels
of all 6 (6 V batteries only have 3) compartments.
Keep the liquid between the min and max mark.
You top the battery up with distilled water or deionised water
which is available from most shops, including food supermarkets,
DIY shops, car shops, motorcycle shops and maybe even petrol stations.
You must only use distilled water or deionised water,
do not use any other types of water. Distilled water or deionised water is also used
in domestic steam irons and other devices,
do not use it if anything is added to it (like perfume).
Never use battery acid unless it's a new battery just before or after its first charge.
Each compartment can be opened from the top of the battery.

For more information about batteries, faults and charging see Electrical Faults in the Basic Fault Finding page.

Air Filter

When to clean or replace the Air Filter has nothing to do with mileage, it has to do with how clean the air is in your country.
You only need to replace the Air Filter if it has holes in it or you cannot clean it.

In the UK for example the air is so clean that you may never or hardly ever need to clean the filter for the life of the engine.
In another country that for instants has a desert, you may have to clean the filter every few miles in a sand storm.

You can always have a look at the Air Filter to see if it needs cleaning or replacing
(the cleaning instructions below will show you how).
But you can also simply check the spark plug or check it when the engine runs rich (loses power and other things);
see Spark Plug in Mechanical Faults section of the Basic Fault Finding page.

The Owner's Manual tells you how to clean the Air Filter (if you do not have it, see below).
The Air Filter is behind the right hand side cover of the bike (if not it must be behind the left hand side cover, very unlikely).
Remove Air Filter.

If it's paper type,
tap it and blow (in reverse so air goes the opposite way through the filter)
with a pump or compressor (front disc brake model is paper type).

If it's foam type, you can wash it.
Wash the foam filter in white spirit or warm water with detergent (washing up liquid).
Make sure you rinse out all the white spirit or detergent thoroughly with loads of water.
Make sure the foam is 100% dry (see below about squeezing) then soak in
SAE 80 gear oil, SAE 90 gear oil or SAE 30 (often sold for Lawn Mowers) engine oil.
Gently squeeze out excess oil (else exhaust will smoke until it's burned off).
Squeezing should be more like pressing,
do not wring it out (do not turn one bit one way and the other another) else you will damage the foam.

Throttle cable

If it stretches, adjust it to 2-6 mm free play,
the adjuster is on the throttle cable,
there's a lock nut to undo first.

I was told by a Honda dealer that
the throttle cable is maintenance free on the front disc brake model,
if it wears out you need to replace it, you do not oil it.
I do not know if this applies to older models or not (see Clutch Cable page for oiling).

Ignition Timing

All the 1995 ? (S & T models) onwards, Honda CG125 bikes have Electronic Ignition,
also known as Capacitor Discharge or CDI, it requires no maintenance.
The only reason to change the Electronic Ignition Timing setting,
is to bodge a worn out engine (if you are too lazy to replace the worn out parts).
Some people change the Electronic Ignition Timing setting to try to get more power out of the engine
(not advised, it's not a sports bike engine).

If you have a Honda CG125 before 1995 ? (before S & T models) it could still have the old Points system,
this requires maintenance a bit like the Valve Clearance.
The Points system wears out (can buy new points),
is less reliable and does not work as well as Electronic Ignition (lack of power at some engine revs).
If you have the Points system, below are the details you need for the Honda CG125,
you will need to search the internet for a universal guide for Points.
You could instead look at the Haynes Honda CG125 workshop manual but it's not really needed.
The Points are behind the left hand engine cover (gear lever side).
Follow steps 1 and 3 from the Valve Clearance page, but instead of aligning up the T, align up F.
The point's gap should be ideally set at 0.3 mm (0.012 inch) to 0.4 mm (0.016 inch), 0.35 mm (0.014 inch).


All of the following could transform your bike if it has not already been done.
Suspension without enough grease or oil in will not only make the bike uncomfortable when going over bumps,
but will also substantially affect the cornering ability round bends and lift the wheel off the road (not to mention corrosion).

Also see Rear Suspension in General page

There is a strong probability when the bike was manufactured,
that the rear swinging arm bolt was not greased properly (or at all).
It should also be re greased every few years as well,
a red coloured grease is ideal, see Red Grease in Brakes page.
It's a very quick thing to do, if you're really not confident to do it yourself,
get a mechanic to do it, watch them work, may only take 10 minutes (so do not pay a fortune for it),
they should also have the grease.
If you find no mechanic will do it cheaply, rounding up 10 minutes work to 30 minutes or an hour,
in the UK see if they will do it when you have an MOT.

Front suspension, the forks should have their oil changed every few years as well,
it's even possible the manufacturer did not put enough in the first place.
So I recommend you change it,
you need to find out how much to put in (ask a dealer for your bike version, Haynes are not always right).
The Front Disk brake model should have 74.5ml of 10W Fork Oil per fork,
do not assume this is the correct amount for other models of CG125.

When you change the fork oil, it's probably a 10w weight motorcycle fork oil you need.
It's also the perfect time to fit fork gaiters to protect the chrome in winter.
To see how to remove the forks, see Fork Gaiters in Riding In Winter page.

But make sure you slacken the cap on the very top of the fork leg first (that's where the oil comes out).
When you have the fork out, remove the cap at the top and turn it upside down,
let the spring fall out and let the oil run out for around 20mins.
Then move the chrome part in and out of the leg a few times to get anything left out.
Then put the correct amount of new fork oil in and put the spring and cap back on.
See Fork Gaiters in Riding In Winter page again to see how to put fork back in to bike.
Then you will be able to fully tighten the cap.

How to replace the Headlight Bulb

For information about different headlight bulbs; see Headlight Bulb in Accessories page.

The following is for the front disc brake model, I would not be surprised if it was also correct for the front drum brake model.

The original bulb is a 12v 35/35w incandescent type with a BA20d connection to the bulb holder.

Remove the 2 screws underneath the headlight (just behind the chrome rim), they will be very tight.
Both screws will have a washer and a plastic tube that goes through the hole, make sure you get both of them out as well.

Pull the bottom of the chrome rim away from the bike to remove the headlight (this will be hard so use brute force).

When you remove the headlight,
you will find the headlight wire half way along has a connector, remove the connector (it has a little clip).
The headlight should now be totally disconnected from the bike.
Look at the rubber bulb holder, there's a small spring connecting it to the headlight; remove the spring at that end.
Pull the rubber away at the edges, then lift the bulb holder out,
it has a little piece of metal sticking in to a slot in the headlight at the opposite end to the spring.

You should now put a pair of clean gloves on, this is critical if you are touching a Halogen bulb,
it's also recommended for any type of bulb.
I use normal disposable gloves that are totally clean;
if you touch the bulb without gloves you must clean it with a soft cloth and methylated spirit.
If you do not clean it,
the bulb is likely to fail (overheat and destroy itself) when you use it next due to the natural oil in your fingers.

To remove the bulb, push it in to the bulb holder and twist it anti clockwise.

To put a new bulb in, you will find it will only go in one way round, the 2 bayonet arms are different sizes.
You may think a Halogen bulb has so much metal you would not touch the glass / plastic sensitive part,
but it's impossible, you must wear gloves.
Push the new bulb in to the bulb holder and twist clockwise.
Find the little piece of metal sticking out of the bulb holder (opposite side to the spring); put it in the slot in the headlamp.
Push the rubber back in to place to create a seal; reconnect the spring to the headlight.
Reconnect the headlamp wire connector to the bike.
Put headlamp back in to bike and line up the screw holes and put the 2 screws back in with the bits that were with it.

Ethanol in Petrol Warning

This section was last updated in March 2012.

Ethanol is very bad for all petrol engines and will cause extreme damage if you are not careful (more details below).

The percentage (amount) of ethanol being added to petrol has and is increasing every year in the UK
and many other countries, due to governments trying to reduce the amount of petrol used.

As a result many petrol engine manufacturers ether refuse to mention if they can be run on ethanol or advise you not to use it.
Even if they say it can be run on ethanol,
the good manufactures will say you must remove it from the vehicle if stored for months.

Trying to avoid buying petrol with ethanol in it is impossible (or almost) in the UK and many other countries.

The higher the percentage (%) of ethanol in the petrol the worse the problem.

The main problems with ethanol are.
It prefers to mix with water instead of petrol.

Since all petrol tanks have a breather hole / tube,
moisture from the air outside gets in to the tank and turns to water (condenses).
Petrol and water will not mix, petrol will always sit on top of water even if you mix or shake it around.
So over time more and more water will get in to the tank and sticks to the ethanol.

When too much water sticks to the ethanol, the water and ethanol will drop to the bottom of the petrol tank.
No matter how hard you try, there is no way to get the petrol to mix back in to the ethanol.

If the water and ethanol sitting at the bottom of the tank is low enough,
it hopefully will not be high enough to go down the petrol pipe.
Since ethanol increases the petrol octane, losing it means the engine may not start or will run very badly,
but no damage will occur if you realise the problem and replace the fuel.

The real problem happens when you get pure ethanol + water going down the petrol pipe.
Ethanol is a very strong cleaner; it will dissolve glue, sealants, rubber and some plastics.
The water will corrode (rust) things.
Even if it only happens once, it's often too late;
petrol pipes and everything else between the petrol tank and the engine are often ruined.
Even if you have the best vehicle designed to run on 10 or even 20% ethanol.
The repair bill is likely to be incredibly high, so should be avoided at all costs.
Even some petrol tanks are sealed with glue or made of plastic, so even they can suffer.

Parts of the fuel system between the petrol tank and engine are also full of fuel and exposed to the outside air.
So they are also at risk.

The amount of water that gets in to the petrol tank will depend on the weather.
It's also dependant on time, the more time the more water gets in.

UK and Europe have the same rules about Ethanol since Europe writes the rules.
Up to 5% ethanol they claim can be used in any petrol engine and does not have to be mentioned on the petrol pump.
Ethanol over 5% must be mentioned on the petrol pump, since many engines cannot run on ethanol above 5%.
In the UK as of 2011 no petrol is available above 5%, but France and Germany have 10% ethanol (UK may go 10% in 2013).
The European rules state the symbol for 10% ethanol in petrol is E10 on the petrol pump;
E stands for ethanol, 10 stands for the percentage (%).
The European rules also currently (as of 2011) state that where E10 is sold,
E5 or lower must also be available at the same petrol station.
They say this normally means, E10 is only available in petrol stations that sell super unleaded as well as normal unleaded.
The super unleaded is E5 or lower, the normal unleaded is E10.

The very simple message about all this ethanol business is avoid E10 in any engine.
But any percentage of ethanol is real trouble if left in the vehicle for months.
So remove all the fuel from the petrol tank and run engine until it stops to remove the rest of the fuel from the system.
If you forget to do this, whatever you do, do not try to start engine,
since it will suck pure ethanol in and immediately damage everything between tank and engine,
you must remove all fuel from petrol tank first and put fresh fuel in.

When E10 was introduced in France and Germany, they had to have a massive advertising campaign to inform the public.
They told the public to look in their owner's manuals to see if their vehicles can run on E10.
But they also told them to check with the manufacture
even if it's not mentioned in the owner's manual since they may have changed their mind.

E10 also has many other major problems,
even in engines designed for E10 and only have fresh (less than 1 week old) petrol in the tank.
That's because it is so strong at 10% that it will attack many parts of the fuel system and engine,
even in modern fuel injected quality cars.
An engine that claims to be suitable for E10, simply has parts that are resistant to Ethanol,
but they are still eventually worn out by it.

Another major problem with ethanol (especially at 10%) is it has less energy than normal petrol.
This means worse petrol consumption.
But also means the engine runs leaner unless the engine automatically adapts.
Running to lean results in engine temperature increasing (that is a very bad thing for engine life),
poor drivability (hesitation, surging, poor throttle response etc.).

In a carburetted engine (even ones that claim to be E10 compatible), there is no way for it to adapt.
Motorcycle carburetted engines in the UK sold between 2004 and 2008 had to meet Euro 2 Emission laws,
which means they are running very lean in the first place (2001 to 2003 is a bit better, but 2009 onwards is far worse),
So making them any leaner will make things even worse.
Especially in winter, since the air is denser (since it's colder) which makes the engine run even leaner.
The only hope to richen (the opposite of lean) the mixture with these engines is to allow the air filter to bung / clog up
(simply do not clean or replace it), so less air gets in to the engine.
But you do not want it to become too rich else you will also have problems.
The only other option would be to change some of the parts inside the carburettor to richen things up.
But what size parts and where to get them from may be very difficult to find (as well as making sure they are E10 compatible).

If you think a Fuel Injection engine will adapt to E10 perfectly think again,
since most cannot (including ones that are E10 compatible).
First of all the computer in the Fuel Injection system needs to have been programmed (mapped) for it.
Even if it has, you are probably thinking that since all Fuel Injection systems have an oxygen sensor,
it adjusts the engine to automatically richen / lean it to get the perfect fuel mixture.
The problem is at full throttle not all Fuel Injection systems use the oxygen sensor.
So unless you have a knock sensor (adjusts to the quality / octane of the fuel by adjusting the ignition timing),
you will have problems like a carburettor engine (see the paragraph above).
Running to lean with a fuel injection system may be worse than a carburetted engine.
Since the fuel system often does not like excessive heat (especially if the fuel pump is above the engine).
Also motorcycle fuel injection engines sold after 2009 have to meet Euro 3 emission laws,
which means they are running very lean in the first place.

More details about the problems with Ethanol
can be found from Classic Car and Classic Motorcycle places since they have more experience.
Also lawn mower places are starting to notice and petrol boats and light aircraft are suffering.

A simple test for ethanol in petrol is.
Get a clear container (with a top) that can withstand petrol.
Put a mark around 25% from the bottom of the container.
Pour water up to the mark.
Fill the rest of the container with petrol.
Put the top on and shake / turn upside down.
Turn container upright.
Immediately the petrol will separate from the water.
If there is any ethanol, it will have mixed with the water; since both are transparent they will both look the same.
So if it looks like the water is above the mark, you have ethanol, the higher it is above the mark, the more ethanol there is.

Storing the bike for months

See Ethanol in Petrol Warning
You must get the petrol out of the carburettor or it can go off and block the carburettor over a long time
(often blocks the idle part of the carburettor).
You can get the petrol out by switching the petrol tap off and running the engine until it stops.

Change the engine oil, see Engine Oil page.
Oil the chain; see Chain Oiling in Chain page.

Empty the petrol tank and spray inside with anti-rust oil.
The only alternative is to remove the petrol tank and leave it in the house.

Remove the spark plug and put a tablespoon of engine oil down the hole.
Cover the spark plug hole with a cloth and turn the engine over several times.
This is best done with the kick-start; if you only have electric start it's best to recharge the battery afterwards.
Then put the spark plug back in, see Spark Plug page.

Remove the battery, you should also slow charge it every month to stop it going off, see Battery section above.

Pump up the tyres regularly.
Take the weight off both tyres by putting blocks under the bike, if you cannot turn the wheels regularly.

Get bike working after storing for months

See Ethanol in Petrol Warning
Charge the battery and do not be surprised if you need a new battery, check fluid level if it's maintenance type,
see Battery section above.

Change the engine oil if it's been stored for more than 4 months, see Engine Oil page.
Oil the chain; see Chain Oiling in Chain page.

If the petrol tank was left empty with anti rust oil sprayed in it, drain off the excess and fill with fresh petrol.
If tank was left with petrol in, it may have gone stale, empty it or dilute it with fresh petrol if you have trouble.
If petrol tank was left with petrol inside it but not full, expect rust inside tank,
it should fall to the bottom of the tank, the reserve petrol tap position could pick up the rust and block carburettor.

If carburettor was left with petrol in the petrol could have gone off and blocked the carburettor, try fresh petrol.

If you still have a petrol related problem see Petrol section in Basic Fault Finding page.