Honda CG125 won't start

[WheelieKid]

Just bought a 2007 Honda CG125.

Rode it at the weekend nothing was wrong with it except when I came home it did not want to idle.

Same problem today except when I stopped at a junction it cut out and now won't start (electric start only model).

I was told the starter was replaced last year by the previous owner.
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A̶p̶r̶i̶l̶i̶a̶ ̶M̶X̶1̶2̶5̶ Honda CG125

[bikenut]

Purchased from a dealer ? So has a warranty...

I assume it has fuel ( petrol ) and the starter whizzes the engine over ?

How is the engine oil level ?
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nuts about bikes

[WheelieKid]

[bikenut]

So no warranty...

How many amps is the battery drawing on the charger gauge ?

Is the battery getting warm in one area and does it need topping up with distilled ( called deionised these days ) water.

You have a digital multi meter and wiring diagram ?

When the battery is back on and the plug cleaned, gapped and refitted, check choke operation.

When engine running and at idle, with no multimeter, turn on headlights and increase engine revs, do light grow brighter ?

No need to rev it till it explodes, just increase revs and watch lights.

Some research necessary as lights may be ac rather than DC on this bike, and does it have a carb ?

If not known check via CMSNL...
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nuts about bikes

[KiwiBob]

Plugs black .. you have not left the choke on have you?

[MCN]

It will run with the choke on half.
They have two positions.
Full choke for starting.
And a half choke. For no apparent reason.

Start on full choke.
Flick it off after a few minutes.

If you flooded the engine. Most probably now.
Too much fuel and the spark won't light it. Because there is not enough oxygen in an over-rich fuel mixture.
You need to remove the excess fuel from the engine.

Choke Off
Throttle held fully open on the stop.
Crank the engine over for a couple of second.
That will blow the excess fuel out.
Choke full on.
Hold throttle just a baw hair off fully closed.
Crank the engine.
It should then start.
Let it run on the choke until it can run without choke.
Takes about 5 mins.

If it still won't start then you should check spark is good.
Spark is generally good enough to start even the most shit engine.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Robby]

Last time I was working on one of these there were two main problems:

1. Water in the fuel. Quite a lot of it. Turn the fuel off, pop the fuel pipe off the carb and into a plastic bottle, turn the fuel to reserve, let about half a litre run into the bottle. Water will settle to the bottom. You don't want any water in the fuel. If you see any, drain it all out and then also drain the carb - little screw on the bottom.

2. You're probably using the choke the wrong way round. I hate the carbs on those bikes, I always get things back to front.

The battery should recover from charging, but it might just need to be replaced.

[WheelieKid]

[MCN]

Remove the air filter, if it has one, and try.

Plugged air filter will increase fuel mixture and could cause the issues you are having.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Robby]

There is an idle adjuster screw on the side of the carb. Screw it in to raise the idle, out to lower it.

Before you fiddle with that though, check over the basic service parts. For a CG that just means checking/changing the air filter, changing the spark plug, making sure it has some oil in the engine.

As as I said last time, check for water in the fuel.

CG125s can get seriously neglected, because they keep on working in a state that other bikes would have given up. It also means that diagnosis over the internet is less straightforward, because I have no idea what state your bike is in.

[WheelieKid]

[Easy-X]

[Robby]

A bit of water in the fuel tank happens from sitting, particularly if the tank is not full. Condensation from the air collects on the steel sides of the tank, and rolls down into the petrol and sits underneath it.

However, the amount of water you get from this is negligible. If the tank has sat long enough for water to be a problem to the bike running, the fuel has gone off and the tank has probably rusted quite a bit as well. Multiple years.

More typical, the rubber sealing ring under the fuel filler cap goes hard and stops making a good seal, combined with the bike living outside in the rain, without a cover. Leave a bike like that for a couple of months over winter and you'll have a pint of water in the bottom of the fuel tank.

Ethanol is a whole different bag of issues. On the one hand, it's hygroscopic so it absorbs water out of the air and eventually allows the water to separate out. On the other hand, it's hygroscopic so it will absorb small amounts of water without affecting its viability as fuel. For daily use, that means I prefer it - water doesn't get to accumulate at the bottom of my fuel tank, it gets absorbed and burnt with the petrol/ethanol mix.

[WheelieKid]

[Easy-X]

With a multimeter the basic checks are:

Voltage of battery (should be >12V, 13~14V ideal)
Voltage of battery when turning over (if it turns over) it'll drop a bit and dance around but give us a rough idea of what it does.
Voltage of battery while idling and with some revs (again, if you can even start it!) just to get an idea of what the charging system is pushing to it.

After that you can do things like checking fuses with the continuity check feature of the multimeter, use the voltage function to trace the path of the hot wire, e.g. "hmm, red wire goes from battery to ignition but I'm not seeing any voltage there..." and so on.

A whole world opens up! Just remember that the frame of the bike is used as a common earth (i.e. connected to the negative terminal of the battery.)
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Nobby the Bastard]

I'd be looking at the connections to the ignition switch and rh switchgear.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[bypass2]

is the petrol tap working.

[WheelieKid]

After taking it to the mechanic I had found out that the valve was mushroomed and also a new valve seat was needed.
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A̶p̶r̶i̶l̶i̶a̶ ̶M̶X̶1̶2̶5̶ Honda CG125

[stinkwheel]

[WheelieKid]

[stinkwheel]

I still find that improbable, I'd have expected it to throw a pushrod first. They usually just bounce the valves if you over-rev them.

I think that must be some sort of record.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[WheelieKid]

[stinkwheel]

[WheelieKid]

[Nobby the Bastard]

My experience of cg125s is that they refuse to be thrashed by design.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050