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 tells you to 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 this Servicing page as soon as possible.
How to find your bikes Tool Kit and Owners Manual
How to replace the Headlight Bulb
Get bike working after storing for months
In the UK, the shop probably told you, that if a Honda dealer does not service the bike, the Honda 2 year warrantee is invalid,
this is a deliberate lie to increase their profits, since there servicing costs are very expensive for hardly any work.
If you read the UK warranty book that comes with the bike, it states anyone can service the bike and the warranty stays intact,
the only way to invalidate the warranty is if you do not do the servicing correctly.
For instance if you forget to change the oil at the correct mileage and the bike then develops a fault that is due to the lack of oil change,
you can not claim on the warranty to fix that fault.
But if you have not changed the oil and the petrol tank rusts through (very unlikely), you can make a warranty claim for a tank.
I have confirmed all this with the Honda UK helpline who were emphatic about this.
I also remember the UK government passed a law about this a few years ago,
to stop all motor vehicles begin forced to be serviced at the manufacturers dealers, in order to keep the warranty.
Of course a dealer has no legal obligation to carry out warranty work unless you bought it from them.
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.
Its not uncommon for the owner to remove and store the Owner's Manual away from the bike, and do not return it 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, 3 cm high on the Front Disc Brake model.
It has the very basics of tools needed for the bike, like the rear suspension adjustment 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 the 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 only one end of the seat (one on each side).
They are usually underneath the back of the seat, but some models are at the front (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.
You can buy the Haynes Honda CG125 Owners Workshop Manual, this can probably replace the Honda CG125 Owner's Manual.
It also tells you how to service and repair the bike.
You can buy it in printed form or download it direct from the manufacturer.
Make sure it supports your model year, you will also find that it tells you everything for 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.
Its behind the left hand side panel, if not it must be behind the right hand side panel (very unlikely).
The original battery in the front disc brake model is maintenance free, so do not touch it.
If you have a maintenance type battery, 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 (never use battery acid unless it's a new battery just before or after it's first charger) which is available from most shops,
you can save money by buying the stuff for domestic steam irons from your supermarket, its the same stuff and says distilled water.
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.
If you have the Owner's Manual, use it as a reference to the following, it's not essential to have it.
The Owner's Manual states change every 2500 miles (1850 miles front drum brake model),
I would change it at 2000 miles (1500 miles front drum brake model) for a mixture of short and long journeys,
if you are mainly doing short journeys, change it every 1000 to 1500 miles (1000 miles front drum brake model).
There should never be a need for less than every 1000 miles.
The best advice is to treat the mileage in the Owner's Manual as an absolute maximum.
Short journeys are bad for oil, the engine does not get up to heat and condensation occurs,
this means the oil will become dirtier per mile, than on normal journeys, so you need to change the oil at less mileage.
Its probably a good idea to change the oil every year, even if you have not done enough miles.
Tools Required.
24mm Spanner or Socket to undo oil drain nut (left hand side of bike near the bottom), front drum brake model may need another size.
Front Drum Brake model may (depends on version) have another oil drain nut under the bike, needs another size of spanner, do not no what size.
Container to collect old oil (2 litre ice cream container or anything).
Rubber gloves to protect hands from oil.
Small funnel to help pour new oil in to bike (washing up liquid bottle, water bottle, pop or squash bottle cut in half and 100% cleaned and dry).
Warm up engine for at least 3 minutes (idling and revving).
You will get more oil out if you take the bike for a long fast ride to get the oil as hot as possible, the more oil you get out the better.
I have found 5 miles at 40 mph in 5th gear (nut not to hot) does not get as much oil out as 17 miles with over half of that over 50 mph in 5th gear (nut very hot).
Even with gloves on the nut is to hot to touch on the 17 mile trip, you end up dropping the nut unless you hold it with many layers of cloth or towel to insulate it.
Switch off engine and immediately
Put container under the bike to catch the oil
Put rubber gloves on hands
Remove the dip stick (black plastic knob, right hand side of bike, it measures the oil in the engine).
Remove the drain nut (see below, if the gear change lever is in the way see Gear change lever in General page).
The Front Drum Brake model may (depends on version) have a drain nut underneath the bike,
this should be used to drain the oil (not the oil filter / drain nut).
The drain nut (24mm, left hand side of bike near the bottom) has a large,
spring & oil filter (metal gorse like a thimble that protects a sewing operators finger, use the spring to wiggle the filter out) sitting behind it.
The filter at one end is round with about a 2.54cm diameter, its about 2.54cm long.
The spring is round and about 2.54cm diameter, its about 5.1cm long but only has around two 360 degree turns in it, the spring is not compressed much.
Clean filter with a suitable liquid like petrol (don't leave in petrol to long or it will eat the rubber).
If you clean the filter with petrol, the petrol will evaporate very quickly in the open air.
The front disc brake model claims you only need to clean the oil filter every 7500 miles,
I would clean it more often, to stop the centrifugal oil filter having to clean the oil.
If you find anything major in the filter, look and think, if your worried show it to a mechanic,
its normal to get a bit of metal in there when an engine is running in.
The Owner's Manual for the front disc brake model claims the centrifugal filter should be cleaned every 7500 miles.
The centrifugal oil filter is inside the engine and never needs to be cleaned if you keep the other oil filter clean and change the oil on time or before,
according to the mechanics. For more details see Centrifugal Oil filter below.
The oil will continue to drip out of the bike for ages, rocking the bike on the centre stand might help get more oil out, also leaning the bike to the left slightly.
When its stopped dripping, or you can not wait any longer, put the filter and drain nut back on.
Pour 900ml (1 litre bottles often have marks down the side) of 10W/40 new oil (see Which Oil quality to use below) in (put oil drain nut back in first),
Check the oil level is at the max mark or above (see How to check the Oil level below),
warm engine up (screw dip stick back in first) for 3 minutes (idling and revving slightly in neutral) and check oil level after its been off for 5 minutes.
Remove dip stick (black plastic knob, right hand side of bike, it measures the oil in the engine), wipe the oil off,
put dip stick back in bike but do not screw it in, the xxxx marks at the bottom of the dip stick should face sideways (not up and down),
take dip stick out of bike and look were the oil has gone up to on the dip stick,
the xxxx marks on the bottom of the dip stick mark the min and max mark.
Its much easier to see the oil in natural daylight than with a light bulb.
There's no harm going slightly above the max mark, but not excessively, never run the engine below the min mark.
Make sure you check the oil level with the bike on level ground.
Since the free 600 miles service I have used real semi synthetic oil.
Since I was running in the bike, I do not know what it did to the performance, but the clutch felt a lot smoother.
There is an argument that I should have waited for the engine to run in before using semi synthetic oil.
Real semi synthetic oil will protect the engine when cold and also at high revs, it also will not break down as fast at high engine revs,
so the oil will do more miles before needing to be replaced (I would still change it early anyway), unlike mineral oil / fake semi synthetic oil.
Many oils claim to be semi synthetic but are in fact normal mineral oil. Silkolene Comp 4 is semi synthetic for sure.
Best way to find out is to look at a manufactures whole range and buy the one just below the fully synthetic in price.
I would only use motorcycle oil, car oil might work but might cause trouble in the long term.
There are so many technical reasons why not to use car oil, even the highest quality car oil, just do not risk it.
I would not use a very cheap or unknown brand of motorcycle oil, since it could clog up the centrifugal oil filter and or even damage the engine.
It's ok to upgrade from mineral oil to real semi synthetic, but a bad idea to go back again, the engine could develop a fault.
Everyone except the oil companies advise against using fully synthetic oil, since its to good and a waste of money and could cause clutch slip,
clutch slip has however been said to be a bad rumour, but the idea has stuck in peoples brains.
Honda sell their own oil for all Honda bikes. They only sell mineral and semi synthetic.
There must be a reason why they do not sell fully synthetic, so I have not used it.
If you want an explanation about oil and what is and what is not synthetic and why you would want real semi synthetic,
I will need to be more precise.
Mineral oil comes out the ground.
Synthetic is supposed to be 100% man made.
One company messed around with mineral oil and claimed that since a person messed about with it, it was now semi synthetic,
there was a legal case and they won.
Based on that principle you could milk a cow and boil the milk and claim its now semi synthetic.
All they did to the mineral oil was molecularly convert it.
There are two 100% man made products and they are real synthetics, since they are nothing to do with mineral oil.
One is Ester, this is what protects your engine when cold and also at high revs.
The other synthetic product is PAO
Ester clings to the parts in the engine and lubricates them,
Mineral oil does not cling as well when the engine is cold, this results in a lack of oil lubricating the engine,
which is why most engine wear happens when the engine is cold.
Mineral oil also loses its viscosity (thickness) at high temperatures, so when you are at high engine revs, the oil thins and loses its lubrication abilities,
mineral oil also breaks down at high temperatures so must be replaced more often.
Ester must be mixed with PAO or Mineral oil, else your engine would smash itself to pieces.
If you see on a oil label, fully synthetic, it will have no mineral oil in it. It will have a mixture of PAO and Ester or just PAO.
Ester costs more than PAO, so PAO only oil will be much cheaper and useless. I have not seen any PAO only oil for motorcycles.
There are often two grades of fully synthetic motorcycle oil, both have PAO and Ester, the quality and mixture is better in the more expensive version.
The centrifugal oil filter should not need to be touched as long as the oil has been changed at the correct mileage or before (see Oil change above).
But some people change the oil every 5000 miles or never, this means the oil becomes very dirty, the filters then become clogged up and need to be cleaned.
When the oil becomes very dirty you will notice the colour change and other things,
if you change the oil at the correct mileage or before (see Oil change above), the oil you drain out should be similar or identical to the new oil.
Different brands and models of oil can have different colours.
Most if not all mechanics never clean the Centrifugal Oil filter, including the Honda ones, unless it has clogged up due to lack of oil changes.
The Owner's Manual for the front disc brake model claims the Centrifugal Oil filter should be cleaned every 7500 miles, but the advice is to ignore it.
If the Centrifugal Oil filter has clogged up due to lack of oil changes, you will have to clean it or pay a mechanic.
Unless you are good mechanically or have a Haynes or other Honda CG125 workshop manual, do not try it yourself.
You need a special tool to remove it, the specifications of the tool can be obtained and manufactured at most motorcycle servicing shops.
The tool required may depend on the model of Honda CG125.
The Haynes Workshop manual for the Honda CG125 should tell you and may even tell you how to make the tool yourself.
You also have to remove the oil, clutch cable, exhaust, foot rests including the metal bar they are on, brake pedal?
If you have a kickstart, you have to remove that as well.
Remove the right hand side engine cover, gasket (may need to buy a new one), oil filter cover.
You then have to stop the engine from turning (put bike in gear and apply rear brake).
Then you can unscrew and remove the filter.
Remove the spark plug cap on top of the spark plug (just pull it off with a slight twist).
Remove the spark plug with the tools in the bike (see How to find your bikes Tool Kit and Owners Manual above).
If you have no tools, you need a 18 mm spark plug tool that's long enough to go over the top of the plug and reach the nut.
if it's to tight to turn, take the bike for a ride to get it up to heat or if it's already hot, try it stone cold.
Screw a new plug in hand tight (with no tools), then put the spark plug tool on and tighten it 1/2 a turn.
If you are fitting a used spark plug, hand tight again but only use the spark plug tool to tighten 1/8 to 1/4 turn. A turn is 360 degrees.
Put spark plug cap back on (just push on with a slight twist).
Important Spark Plug Information
When purchasing a new spark plug, there are 2 different models of spark plug for 2 different designs of Honda CG125 engine.
Lots of people and some mechanics can easily make a mistake since it’s often very hard to work out which one you need.
If you have the Owner’s Manual, it should tell you.
If you have the original spark plug put in the bike when manufactured you will no the correct spark plug model.
But shop / mechanics often use spark plug manufacturers recommendations for Honda CG125 and they are often wrong or misread.
The Haynes Workshop manual is also often used and misread (very easy to do).
The two different spark plug models are
NGK DR8ES-L
NGK DPR8EA-9
NGK is the name of the manufacture and the rest is their part number.
Different spark plug manufacturers make equivalent spark plugs but have different part numbers.
The spark plug manufacturers do have conversion charts so you can convert from one make to another.
NGK is regarded by most people as the best and Honda currently fit them as standard to the Honda CG125.
As a guide, the older the bike, the more likely it will use the first spark plug model above.
The newer the bike, the more likely it will use the second spark plug model above.
If you can find your Honda CG125 model number and give it to a Honda dealer, they should be able to work out which spark plug you need.
But don't let them simply go by the year the bike was built, only the model number will give the correct plug.
That's because Honda CG125 are built in several different country's, one country could make new models and another could always stay making old models.
Spark Plugs based on year in the UK for example will assume you have a model imported by Honda UK,
but loads of Honda CG125 in the UK are not imported by Honda UK and are often old model designs (often a 4 speed gearbox and old fashioned bodywork).
You might be able to find your model number on the chassis near or behind the left hand side panel, otherwise you need to find the frame number,
the Haynes Workshop manual or a Honda dealer may be able to convert the frame number in to a model number.
Important Spark Plug Information
If you need a NGK DR8ES-L spark plug (see Which Spark Plug Model above to find out), you need to set the gap (search the internet) to 0.7mm yourself.
All of the information below only applies if your engine uses the NGK DPR8EA-9
The book tells you to clean and check the gap of the plug every 2500 miles and replace every 5000.
You do not need to check the gap of a new spark plug,
since its preset at the plug factory to the correct gap (NGK brand is for sure and is set to 0.9mm).
I could not be bothered to clean and check the plug gap at 2500 miles since a new plug only costs £2.99 to £5 dependant on shop.
That means at 2500 miles the plug is only worth £1.50 to £2.50 so not worth the work of cleaning and checking the gap, so I put a new one in.
You need a NGK DPR8EA-9 spark plug for normal riding and a NGK DPR9EA-9 for extended high speed riding,
The extended high speed riding spark plug is stated in the Honda CG125 Front Disc brake models Owner's Manual,
but can not be totally sure for other models, but it makes sense since its the same spark plug but gets rid of more heat out of the engine.
The following spark plug information is for the front disc brake model,
I can not be sure if the same would apply to other models.
I found that 54mph in 5th gear is high speed for the plug and results in power dropping off if left at that speed for 1/2 mile.
The power drop off (plug overheating), results in the bike dropping to 50mph against a strong head wind, if you slow down allot the plug will recover.
I fitted the DPR9EA-9 plug and end of problem = no power drop off and the bikes about 5 mph faster.
If you use the DPR9EA-9 for slow speed (especially idling a lot in traffic jams),
there's a chance the plug will not be hot enough to burn off petrol burning deposits on the electrode and the bike will stutter or stall.
I have not had any problems, but would not use it if I was in city traffic all the time with massive amounts of idling,
of course as soon as you get some speed going the plug will heat up and burn off the deposits.
The petrol quality could also effect this, I use Shell V Power since it has extra cleaners in it.
You can also buy a NGK Iridium spark plug, I got the one that’s equivalent to the DPR9EA-9,
its made a very slight improvement in smoothness, power, pulling power and less vibration.
But its very slight and probably not work the price tag of 3 times the price of a normal plug.
But it will last 2 to 3 times as long. Iridium must not be cleaned or the gap changed. I suggest doing 10,000 miles with one.
The Iridium plug also claims to burn off deposits more than a normal plug at slow speeds, so could help the high speed plug potential problem.
It also claims to require less power from the battery and ignites the petrol better on cold days.
NGK Iridium Spark Plug Conversion chart
DPR8EA-9 (NGK Normal Plug) = DPR8EIX-9 (NGK Iridium Plug)
DPR9EA-9 (NGK Normal Plug) = DPR9EIX-9 (NGK Iridium Plug)
Even O ring and fully enclosed chains need oiling.
Use a motorcycle chain oil, there are arguments for and against motorcycle chain wax so oil is recommended.
Engine or gear oil is not recommended (will just fling off very quickly).
You will no when to oil the chain by looking at it, and or kick the back wheel round and notice the chain going round, if it feels notchy, it needs oiling.
If you do not have a fully enclosed chain, I would check the chain every time it rains when its dried.
I found (without a fully enclosed chain) its not mileage that effects when you need to oil the chain, its time and rain.
To oil the chain, make sure it has no water on it, it's probably best to oil the chain when it's hot just after a ride.
Spray the chain with oil on the inside (the side that makes contact with the sprockets), the oil will fling outwards when bike is used and oil the outside.
Do not spray the outside of the chain since it will just fling off and create a mess every ware.
The best advice is to oil a chain often but not with a lot of oil.
Chain oil is slippery so wipe off any that gets on to the tyre.
Do not ride the bike for at least 1 hour afterwards, else the oil will immediately fling off.
The better the chain oil, the more it will stick on (not fling off), it will also last longer and resist water.
See Owner's Manual and the information below, if you don’t have the Owner's Manual you can manage without it.
Chain Tension should be 20mm (can be 10 to 20mm) in the middle of the chain at the tightest spot.
To measure, put a ruler or stick (with marks on it) next to the middle of the chain (just in front of the rear passenger foot rest?).
Put your finger under the chain and try to pull it up until you feel slight resistance.
Move the back wheel slightly and recheck the chain, keep doing this until you find the tightest spot.
The chain tightness is affected by how much oil is on the chain.
To adjust the chain tension, slacken the right hand rear wheel axle nut (22mm ?).
There are 2 adjusters, one on each side of the axle, they both have 2 nuts (12 ? and 10mm ?, the one on the end is a locking nut).
Put a spanner on both nuts at the same time, and slacken the end one.
Repeat this on the other adjuster.
Tighten both adjusters by the same amount of turns (or wheel alignment will go out), recheck chain tension.
The adjusters should point to little marks on the frame, they should be the same on both sides or the wheel alignment will be wrong.
If your wheel alignment has been checked professionally (part of the MOT in the UK), you do not need to worry about the marks.
One of the adjusters should point to a label on the frame that has a wear indicator, when it says it's worn out replace the chain.
When tightening the rear axle nut,
push the rear wheel in to the bike with your left hand while tightening with your right hand,
do not try to tighten the adjuster nuts, just lock the locking nuts in place,
to check that the adjuster nuts are tight, try to put a piece of paper between them and the frame.
Recheck chain tension and repeat procedure if necessary.
The original chain on the front disc brake model is O ring type, this costs several times more money than a non O ring chain,
but it lasts several times longer and keeps the internal oil inside it due to the O rings.
I advise you stick to the manufacturers choice. Of course a X ring is even better than a O ring but costs even more.
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 can not clean it.
In the UK for example the air is clean enough that you may never or hardly ever need to clean the filter for the life of the engine.
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 (looses power and other things),
see Spark Plug in Mechanical Faults in 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 it,
if its the 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 its foam type, you can wash it.
Wash the foam filter in white spirit or warm water with detergent.
Make sure you rinse out all the white spirit or detergent thoroughly with loads
of water.
Make sure the foam is 100% dry 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
out one way and the other another) else you will damage the foam.
The following applies to the front disc brake model.
I would advise you to also try it with the old model,
but do not expect to have to adjust it by such a large amount or have such a warming up problem in the first place,
since it does not have such strict emission regulations.
Tools required, a small flat headed screwdriver bit (must not have a handle since it would hit bike and not fit)
If the Air Filter is clogged up, it will affect the mixture, so if you are in any doubt that the filter is clogged, clean it, see Air Filter above.
The fuel mixture is set incredibly lean when idling by the manufacturer (to reduce pollution).
This results in the engine taking forever to warm up, cools down very quickly needing choke again and hesitation when opening the throttle.
The dealer may have adjusted it if your lucky.
If not, fully warm the bike up = 10 miles or more at high speed at the end (40mph for 5 miles does not warm it up).
Make sure the outside temperature is between 14c and 30c and you're near sea level (not up a mountain).
Look under the carburettor and find the screw (front right hand side of bike, its the screw sticking out and is not tight), adjust it until you get the fastest idle.
1/4 turn will make a difference, adjust the screw and then wait a few seconds for the engine to react, blipping the throttle is some times needed.
When you have found the fastest idle, you will find that even opening and closing the screw 1/4 turn, will slow the engine down.
If you have trouble hearing if the engine has increased or decreased in speed,
ask some one to stand the other side of the bike or behind the bike (listen to the silencer)
The screw would originally be set to about 1 and 3/4 turns open. Mine ended up at 3 1/4 turns open.
You may then need to adjust the Idle speed screw (see below) if the idle speed is to high, but whenever you touch it, recheck the mixture screw setting again.
If you open the Idle Mixture Screw to many turns, it will fall out,
simply push it back in (it does have a spring and washers inside that will fall off if turned upside down).
If the screw is on the fall out turn part, vibration may make it rotate slightly and drop out.
I have had no trouble at 3 1/4 turns open, its still got over 1 whole turn to go before it would fall out.
I class one turn as 360 degrees.
The Owner's Manual shows a picture of where it is.
On the front disc brake model, look at the right hand side of the bike, look at the right hand side panel,
look half way down the side panel and then just to the right of the side panel. See that small black plastic box.
There's a small flat headed screw on the left hand side of it (almost touching the side panel), that is the Idle Speed screw.
Fully warm the bike up = 10 miles or more at high speed at the end (40mph for 5 miles does not warm it up).
Slow the engine idle speed down to the point were it starts to thump during one of its cycles,
then speed it up until it stops thumping,
then speed it up a fraction more.
The whole idea about what speed to set the idle, on any motorbike engine is the following.
To slow and the bike will stall, nearly fast enough and the engine will splutter or stall now and again.
To fast and the engine will overheat in a traffic jam and burn more petrol than needed.
The gear change is also effected by idle speed, to fast or slow will effect how smooth it is or even stop you changing gear in extreme cases.
The difference in overheating speed and stalling speed is large, so you only have to roughly set the idle speed.
If it stretches, use the adjuster on the clutch lever (behind rubber) to adjust it.
It should have 10 to 20mm (20mm recommended) of free play (slack, before it starts to work) between the lever tip and the handle bar.
The cable needs to be oiled only when you notice it needs it, clutch will feel rough and needs more power.
Don't be surprised to find that's a very long time away.
You can just replace the whole cable, cheap enough if you do not want to oil the old.
To oil the old, unscrew the adjuster nut at the clutch lever and remove cable,
put a small hole in a plastic bag and put the hole over the clutch cable,
tie the plastic bag hole end to the plastic outside of the clutch cable with tape to make an oil tight seal,
hold bag upright and pour some engine oil in to it.
If possible leave bag upright all night (tie it to something in the ceiling),
the oil will run down the cable and out the other end, put something there to absorb it.
Replace the whole cable if oiling does not make it smooth again or some stands have broken or it stretches regularly requiring adjustment.
To replace cable, disconnect it at the handlebar lever and at the other end which is probably on the right hand side of the engine.
Most motorcycle dealers or accessory shops should sell a universal motorcycle clutch cable that will fit.
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.
Free play (slack, before brake works) from the brake pedal to the ground should be 20 to 30mm, adjust it with the nut on the brake rod on the back wheel.
After adjusting, check that the brake light comes on when rear brake is applied, if it does not see the Light Bulbs section in Basic Fault Finding page.
There's probably a brake wear indicator (if not see How to remove and install the wheels in the Bike in the Tyres page to find out how to remove the rear brake),
press the brake pedal down and look at the top of the arm that moves on the back wheel as you press the brake pedal,
look for a small arrow on the arm (may need to be cleaned) and watch it move towards the mark (a piece of metal sticking out) on the drum as the brake is applied.
If the arrow hits the mark when the brake is fully on, the brake shoes need to be replaced.
Replacing the brake shoes is pretty easy see How to remove and install the wheels in the Bike in the Tyres page to find out how to remove the rear brake.
It should have 20 to 30mm of free play (slack, before brake works) between the lever tip and the handle bar, you can adjust it with the nut on the brake lever.
If it needs lubrication, see Clutch cable above to find out how to lubricate it.
How to run in the Front Disc Brake
Front Disc Brake fluid changing
How to run in the Front Disc Brake
When new the braking power is very weak, since its not run in.
The secret to running it in is,
do not clean the disc,
do not brake hard or for any length of time to begin with,
then as the miles increase (pads are running in) increase the breaking pressure and the amount of time,
eventually you need to excessively brake hard and over a long distance to really heat up the pads to run it in.
I did the opposite (cleaned it and no excessive braking) and the result was it never ran in, in the end winter came and the roads had salt on and were soaking wet.
The brake hardly worked at all, with water and salt all over it,
so I had to put far more brake pressure on than normal and it took a long distance to stop,
after a few miles of this the brake doubled in power in all weathers ever since.
I don't no if it was the salt water or excessive braking that ran the brake in but its very important that its done, I have read its the excessive braking that did it.
The excessive braking over a long time can only be done with the disc constantly being soaked with wet roads and or rain so it takes a long time to stop,
the only other alternatives would be a very long steep hill repeatedly, passenger on the back or riding with the brake on slightly (with throttle open).
Be careful putting the brake on and the throttle open, the brake can severely overheat after a short time leading to the pad glazing and the disc warping.
The pads should have a worn out indicator, but if you can not see it, the pads are worn out when there is very little brake pad material left.
If you ever hear or feel what seems like metal grinding against metal, your pads are worn out and must be changed immediately or you will damage the disc.
When the brake pads wear out, changing them is simple, search the internet for information.
According to the Honda CG125 specification its a,
240mm hydraulic disc with single-piston calliper and sintered metal pads.
The original pads are sintered type and made by a good quality manufacturer called Nissin.
You can buy the original pads from your Honda dealer and they cost around the same as other brands.
The part numbers for other brands are EBC FA54, GOLDfren 144, Dunlopad DP107, Ferodo FDB250, SBS 536, Vesrah VD120.
The part numbers do not include the pad material type, the two main types are sintered and organic, some makes only make an organic for that part number.
Sintered are much better at braking in the wet and braking power is less affected by temperature.
Organic has more feel and often generates less heat.
For everyday road use Sintered is normally recommended and fitted by manufacturers on the front.
Each pad material can be designed for different uses, you want one designed for road use or sports not off road.
If the brake is excessively binding, you need to clean the brake, again its simple, search the internet for information about cleaning (its a single piston calliper).
Check the fluid level in the sight glass on the side of the reservoir (next to the brake lever).
Move the handle bars from fully left to right to see the fluid appear and disappear.
When the handle bars are straight see how far up the sight glass the fluid reaches,
note the Lower mark near the bottom right of the sight glass, never let the fluid level drop below this mark.
As the brake pads wear down the fluid level will drop.
Front Disc Brake fluid changing
I advise you to change the fluid if it’s a new bike before the 2 year schedule,
I changed it 2 months early and noticed a substantial improvement in power and feel.
There are several different ways to change the fluid,
you can buy a one way valve brake bleeding system for less than £10 and instructions are included.
Its pretty easy and I recommend you try it, just remember brake fluid eats paint so cover it up.
The smallest bottle of DOT 3 or 4 brake fluid is needed.
Any brake bleeding device will come with plastic tubing to connect to the brake, if you do not buy anything,
you will need transparent clear plastic tubing with an internal diameter of 5mm, available from motor shops and maybe DIY and fish tank shops.
The instructions below are how I replaced the brake fluid, it's a combination of the one way valve system and the non one way valve system.
The instructions might make it look hard and complicated, but it really is very easy, lots of the instructions are not needed,
there just in case something goes wrong (unlikely).
I used the metal one way valve (look for the arrow on it, for the direction of flow) with transparent clear plastic tubing on each end (small tube = brake end).
The plastic tubing was very determined to stay in its coiled up state, you need someone to help you keep it straight,
or you could trap it (I put it through a large funnel which I trapped in the handle of a large bucket).
1. Remove the small black rubber cap on the brake bleed nipple (disc end of brake) and attached the small tube.
2. Unscrew and remove the brake fluid reservoir lid, there's a second lid inside that you need to pull out.
3. Pull the brake lever in slowly (as far as you can without excessive force) and slowly release, repeat this 3 or 4 times to get the pressure up,
then pull it in again slowly and hold while very slowly opening the brake bleed nipple nut (the pressure on the brake lever will reduce,
keep pressure on lever, when lever hits handle bars, keep it there), as soon as fluid flows easily in to the transparent pipe, stop opening the nut.
When the fluid stops moving, close the nut and only then release the brake lever slowly.
4. Repeat step 3 until brake fluid has gone through the one way valve.
5. You can now leave the nut open and slowly pull the brake lever in and slowly release over and over until nearly all the fluid is out of the reservoir,
do not let air get in to the small pipes in the bottom of the reservoir or you will get air in to the system.
6. Make sure you have covered everything around the reservoir since you may spill the brake fluid, which eats paint, even a single drop.
Pour new brake fluid in to the reservoir (must be an unopened bottle, it goes off as soon as it's opened).
Keep repeating step 5 and put new brake fluid in when needed, when the colour of the fluid in the transparent tube changes,
you have replaced all the old fluid in the brake system, if you do not notice the colour change,
you must have changed all the fluid when most of the small bottle is used.
7. If the brake lever looses all or some of its pressure, you have let air in to the system, repeat step 3 to get it out.
8. The fluid in the transparent tubing before the one way valve should not have any bubbles or foaming in it, if it does you need to get them out,
you can try step 3 again, you may also need to experiment with the bleed nut (try opening it less or more),
you may also have to try closing the brake bleed nut before the brake lever touches the handle bars.
9. When finished, make sure brake bleed nut is closed tight and top up the reservoir (never let it drop below the Lower mark).
10. Put reservoir lid back on and then the outside lid, you do not need to tighten screws very hard since its all rubber,
remember how easy it was to unscrew.
11. Any brake fluid that has been spilt needs to be diluted with loads of water to stop it eating things,
it's normal for some brake fluid to have escaped around the brake bleed nut.
12. If you have trapped air in the brake system (unlikely), the brake will have a lack of pressure and feel spongy.
If step 8 does not fix this problem, the air is trapped higher up the system, you need to make sure the brake bleed nut is closed tight,
then slowly pull the brake lever in until it touches the handle bar, then tie the lever to the handle bar while it's still touching, leave it like that overnight.
Then open the bleed nut slowly and hopefully the air will come out. If this still does not totally work, try again, the reservoir lid might need to stay off overnight.
New valves will change their clearances while they run in check every 2500 miles, when run in you will find they do not need adjusting so check every 5000 miles.
Its not recommended to ignore checking the valve clearance but if you do,
listen (helmet off) to the valves at the top of the engine when its running, if they are excessively noisy (clatter, clatter) the clearance is to big and needs adjustment.
If one of the valves goes quiet its clearance is to small and must be adjusted immediately to prevent damage.
Performance drop, bad idling, problems starting or compression drop could mean the valve clearance is to big or small, check immediately to prevent damage.
Valve clearances normal increase due to mechanical wear, but can sometimes decrease.
The Honda CG125 is a pushrod type so valve clearance reduces as the engine heats up.
Tools required (may be different sizes for front drum brake models except for Feeler gauge)
Feeler gauge (available from most car motor shops, thin pieces of metal of different thicknesses, must measure 0.08mm or 0.003 inch)
Torch
Magnifying Glass (depends on your eye sight)
10mm spanner
8mm spanner (high quality, else it will not grip the nut well enough to turn), not needed for front drum brake models.
All of the tools below are only needed if you have 2 round covers on the left hand engine case near the bottom but above the oil drain nut.
10mm Allen Key (6 sided hex key)
6mm Allen Key (6 sided hex key)
14mm socket
1. Leave bike overnight to cool down, this is essential since the valve clearance changes with a hot engine.
If you do not have the two covers in the paragraph below you need to remove the gear shift pedal and remove the entire lower left hand engine cover.
2. Remove the two round Allen (hex) key covers on the left hand side of the engine case (near the bottom, but above the oil drain nut).
(If they will not undo, warm the bike up and then try, once they are off leave bike overnight to cool down again).
The big one is for turning over the engine (you might be able to use rear wheel + 5th gear instead)
The small one is were the marks for valve clearance and timing are (T is for valve and F for timing)
3. You can remove the spark plug to aid turning over the engine but not really needed.
If in part 2 you removed the entire lower left hand side engine cover, find the mark at around 12 to 1 o'clock instead of grove at top of hole, T is not on its side,
turn the generator rotor (round disc) anticlockwise wise (maybe able to use rear wheel in 5th gear instead) instead of 14mm socket details below.
4. Turn engine over anticlockwise with 14mm socket until a small on its side T appears near the outside edge of the disc (don't mistake F for T, F is just before)
(use a torch and magnifying glass since its very small and stamped in to the metal, do not use a house light bulb since its to powerful and will hide it with glare)
line the mark (vertical line) below (maybe next to) the T up with the grove at the top of the hole (only turn anticlockwise since engines don't like going in reverse).
(if your eyesight is to bad ask someone else or T = TDC = top dead centre = Piston at highest point in engine, remove spark plug and search internet)
Ignore all of steps 5 (5, 5.1, 5.2, 5.3) if you have the front drum brake model.
5. To remove the valve cover you first need to remove the air box attached to the valve cover (its on the top of the engine, left side) =
5.1 Slide the rubber air pipe out of the metal hook on the bikes metal frame (underneath the petrol tank).
5.2 Remove the two main bolts (10mm) attaching the air box to the valve cover.
5.3 Remove the two 8mm bolts attaching the air pipe to the top of the valve cover (pipe has a rubber washer),
slide air box + pipes away from valve cover / bike.
If the spanner can not grip,
try a better quality spanner or warm the bike up and then try (let the bike cool down overnight again before checking valve clearance)
or remove the petrol tank & use a socket set / may need an extra thin extension shaft.
To remove petrol tank
Make sure petrol on/off/reserve tap is off & detach petrol fuel hose from petrol on/off/reserve tap
remove left side panel of bike, unclip right side panel where it clips in to petrol tank
unclip petrol tank electrical connection and un hook wire from the bikes metal frame
remove seat (2 nuts underneath rear mud guard on the sides), remove bolt holding tank, remove tank by pulling it towards rear of bike and up
6. Remove the valve cover, its on the very top of the engine, two bolts on the right and one on the left (10mm),
there's a rubber gasket inside a grove inside the lid (do not lose or damage / trap it).
You will find there is a technique to getting the valve cover off, it gets caught on the bikes metal frame and also the valves inside.
You may think its impossible to get out, but there is a way, keep trying all the different angles till you find the technique, brute force does not work.
7. Check that you can rock the valves, if you can not, you are on the wrong engine stroke, simply repeat step 4
If you can not work out if the valves are rocking, they will only rock if there's some valve clearance.
If your on the wrong stroke there's no valve clearance.
8. The valve clearance should be set to = 0.08mm (0.003 in) on both valves, this applies to all Honda CG125 models, there are only 2 valves.
A feeler gauge is available from most car motor shops, a feeler gauge is just a set of metal plates of various thicknesses.
The valve clearance is the gap between the round metal rods (its easy to assume its a single rod since gap is so small).
If the valve clearance is correct, the feeler gauge will feel very slight resistance when moving through the gap.
If you find the valves need to be adjusted, its worth trying to turn the engine over several times (repeat step 4 twice then check and repeat)
to see if it then is correct, there's always a slight variation every time you turn the engine over.
To adjust a valve, loosen the nut on the valve you wish to adjust, use pliers (or hand) to turn the top of the screw
thread (or obtain the proper tool) until the clearance is at the desired amount, then re tighten nut.
Recheck valve clearance after re tightening the nut, if its gone out, loosen nut again and readjust.
If the valve clearance changes every time you tighten the nut, you may have to hold the screw when tightening the nut
or set the clearance slightly wrong so when the nut is tightened the clearance becomes correct.
9. Reassemble everything in reverse order, but make sure the rubber air hose is not trapped on the inside when
attaching air box to valve cover (does not apply to front drum brake model since it does not have one).
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 to 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, this is 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).
There are many Points to Electronic Ignition conversion kits available for many different makes and models of bike, there are also universal kits.
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.
The Points are behind the left hand engine cover.
Follow steps 1 to 4 from the Valve clearance section above, but instead of aligning up the T, align up F.
The points gap should be 0.3 mm (0.012 inch) to 0.4 mm (0.016 inch), 0.35 mm (0.014 inch) is were you should set it to ideally.
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, but check in case.
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 have removed 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, its also recommended for any 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 mentholated spirit.
If you do not clean it, the bulb is likely to fail (overheat and destroy itself) when you use it next.
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 its 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.
You must get the petrol out of the carb or it can go off and block the carb over a long time.
You can probably get the petrol out by switching the petrol tap off and running the engine until it stops.
This is best done while riding the bike, the carb might hold 0.3 miles of fuel.
Change the engine oil, see Oil section above.
Oil the chain, see Chain Oiling section above.
Empty the petrol tank and spray inside with anti rust oil.
If you can not, make sure the petrol tank is full of petrol to prevent rust.
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 kickstart, if you only have electric start its best to recharge the battery afterwards.
Then put the spark plug back in, see Spark plug section above.
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 can not turn the wheels regularly.
Get bike working after storing for months
Charge the battery and do not be surprised if you need a new battery, check fluid level if its maintenance type, see Battery section above.
Change the engine oil if it’s been stored for more than 4 months, see Oil section above.
Oil the chain, see Chain Oiling section above.
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 carb.
If carb was left with petrol in the petrol could have gone off and blocked the carb,
try fresh petrol, if that fails you may have to strip the carb and clean it.