At my wits end with this 125cc, any clues?

[Mutt_Mongrel]

Afternoon all,

My bike stalled at 60mph recently, had difficulty starting, and made a screeching noise when I tried to fire it up. This started happening more and more, particularly the stalling at speed. It's been cold recently so I thought it was the battery. Tested the battery, everything was fine. Took the spark plug out and it was black. Fitted a new plug and it started immediately.

A day later, it stalls again. If I ride at low revs, I'm fine. So I ride slowly all the way home.

I open up the air filter, it's fine.

So my next guess is the carburetor?

[Ste]

What bike is it?

[Mutt_Mongrel]

[rpsmith79]

Sounds like it could be the ignition coil that is on it's way out

Has it started misfiring/stutterng/spluttering and more dificult to start in a morning, these are usually signs of coil breaking down

Should be a relatively easy/cheap replacement on a chinese 125
____________________
Current Bike: Honda CG125 ES4 // Honda CB600FS Hornet // Triumph Street Triple R

[Mutt_Mongrel]

Not misfiring, or sputtering, but the idle has become a little weaker than usual. Has stalled when idling in neutral on a couple of occasions this week.

[rpsmith79]

[Mutt_Mongrel]

I've had the bike for a year and haven't changed the filter. It may be that it wasn't changed in 3 years before that. I looked at the foam, only one spot of discolouration, the rest looks clean.

The spark plug being black tells me that something has to be wrong with the petrol mix. It could be that the coil is also on its way out but I feel there has to be something else going on to make the spark plug black.

[P.addy]

[rpsmith79]

[stinkwheel]

Does it actually have a carburettor? I'd have expected a 2018 bike to be fuel injected.

Screetching noise at startup sounds like a sprag clutch not engaging properly.

When you say the battery is "fine" what did you do to check this?
____________________
“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.

[rpsmith79]

[WD Forte]

It is EFI, so why hasn't the OP summoned the DTCs?
A bad engine temp sensor could cause lot of his problems

It's a typical Gn125 clone engine used in many other chinese bikes
and the bikes are just given a tart up to make it look like a
'wellard real biker' type thing.

Mutts website seems more eager to flog you tee shirts, sweat shirts, caps, hoodie and mugs and shit than useful spares.

CMPO flog many parts for them with far less bullshit
____________________
bikers smell of wee

[grr666]

Made in China, frigged in Birmingham, sold nationwide as a 'British' bike just so long as you you squint like a Chinaman.
Fowlers sell loads of them. I was stood next to their huge marketing display only yesterday while waiting for the keys
to my bike that was in for service.
____________________
Currently enjoying products from Ford, Mazda and Yamaha
Ste wrote: Avatars are fine, it's signatures that need turning off.

[Mutt_Mongrel]

[rpsmith79]

[Mutt_Mongrel]

Professionally serviced: about 18 months ago.

I've changed the sparks, oil, oil filter, pads, and chain in the last four months.
New sprockets going on after I get it started.

[Robby]

So it sounds like there are two symptoms here, not necessarily connected.

1. A screeching noise at startup. My first guess here is as Stinkwheel said the sprag clutch, or something do with how the starter motor connects with the flywheel. Could even be as simple as worn brushes, which are one of those old-fashioned problems that I keep seeing on 125s.

2. Stalling at speed, which I'm interpreting as a sudden loss of power. This is unusual at full power (which is where this engine will be at 60mph). Far more common problem at low power/low speed when it tends to be a fuelling problem.

For problem 1, the starter motor and sprag need to be pulled off and inspected.

For problem 2, I would be going over all the electric connectors in the first place, looking for anything loose or heavily burnt/corroded. It sounds like a loss of power to the ignition or fuel injection. Also assuming the bike is fuel injected (because 2018), but not showing an error code (because one wasn't mentioned).

It could be as simple of worn out brushes in the starter motor and a loose connection to the coil. It could also be a lot more complex.

[Pete.]

[A100man]

[A100man]

[stinkwheel]

Here's a big fat guess for everyone. Maybe the sprag clutch has fragged itself and has littered the rotor area with steel swarf.

Or maybe the rotor's spun up.
____________________
“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.

[Pete.]

[WD Forte]

2018 bike? that's good age for a Chinese 125
time to buy a new one methinks
____________________
bikers smell of wee

[Mutt_Mongrel]

[Mutt_Mongrel]