CB125F not working! Please help!

[Eximus]

Hello everyone,

Firstly I would like to say I cannot thank you enough for taking the time to read this and hopefully help me.

(Especially as this is fairly long as I’m trying to provide as much detail as possible).

Basic bike info: HondaCB125F, 2016 Reg, 4K miles.

What happened: I was riding my motorcycle down a long and very steep hill while staying on the rev limiter (red line) in 5th gear the whole time.

Its very difficult to say for how long I was on the Rev limiter .. probably 5 seconds +. Maybe 6 or 7.

My bikes top speed is usually 65 on a flat road and without the wind in front of me but I think I was doing about 70 as the hill was so steep.

Approximately 10-15 minutes later my motorcycle starts losing power and makes horrible noises. Sounded like noises related to metal parts. Maybe.. Metal parts rubbing each other.

I then pull over after a minute or 2. Switch the engine off for a few seconds. Start the engine again and I’m riding along for a minute or 2 without any strange noises at all.

Then after 1 or 2 minutes of normal engine noise.. I lose power .. I pull over quickly and the engine has not started ever since.

The ignition comes on.. then it sounds like what I’m guessing is the starter motor trying to start the engine but no engine noise at all.

Spark plugs were replaced by AA but this did not fix the problem.

Please can you help? Thank you.

[Mysteriass]

It's them vibes maaannn, loosened up the bolt / key on the magneto rotor thing maaan. Now it can't time itself, know what I'm sayin'.

Drain the oil (Firk through the oil and see if there's any metal in it) and take the magneto cover and the clutch cover off. See if anything obvious reveals itself. Examine all gears and cogs; look for debris. If you find some - or not - look for something fooked.

Sometimes it's a surprise...
How these engine's survive...
Even when metal explodes to pieces...
Inside.

So don't give up hope yet.

See if there's an engine strip down / rebuild video on the tube to give you some help and comparisons.

I'm just giving a first guess here by the way. This is by no means motorcycle mechanic advice and you should absolutely most certainly not act upon this information.

How about a couple of checks for info...

Get the bike on the centre stand or chock it up so the back wheel is clear off the ground. Take the spark plug out. Spin the back wheel while the gearbox is in neutral. Listen for anything strange, then put it in gear and spin the wheel...can you hear anything unusual in the engine? Pull the clutch in and out as you're doing it, does that make the sound any different?

Guess B: You might also need to take the cylinder off so you can take a look at the piston. Maybe the rings blew off. That'll be a piston and a rebore if it all got jammed up in the block. And of course trying to get the debris out of the crank case which is always a good time. If you got lucky it'll have blown the bits out of the exhaust.

[WD Forte]

First thing I'd check is the oil level
Have you checked that and how?
I appreciate your attempt to supply relevant info ( age mileage)
but think it's fair to say you don't sound particularly experienced.

At that age and mileage one would expect it to survive the occasional thrashing but perhaps something's come adrift or worst case
low oil + thrashing = engine trashed.
Who knows?

If you want forum advice, remember it can only be best guess at best so clear almost pedantic descriptions will help others make better guesses.

Your noise descriptions mean nothing
I'd expect to hear the fuel pump spin up briefly at ignition on
then go quiet.
If it keep making a noise you're probably out of fuel
dont trust a gauge, look in the tank.

Next, in neutral and pressing the start button I'd expect to hear the starter motor spin the engine
Normally this is quickly followed by the engine starting.
If you get nasty knocking noises when pressing the starter then
this is serious whether it starts or not and needs to be investigated ASAP
____________________
bikers smell of wee

[Hong Kong Phooey]

Think about the combustion process, then find out which bit(s) are missing.

Common problem areas...
Fuel. If you spray brake cleaner into the intake and crank it does it fire up?

Spark. Can you get a nice fat blue spark from the plug if you ground the threads to the engine and crank the bike?

Less common...
Timing, this is where you'll struggle without a strobe light, but if the timing marks are aligned then chances are it'll be fine. Revisit this if compression is good.

Compression, a tester would help but if it's still the same effort required to kick it over then chances are it's enough. You can hold your thumb on the end of a bit of hose jammed into the plug hole and feel pressure build, not scientific but if there's no pressure at all you're shit out of luck.

The metal grinding sound doesn't sound great but if it ran again then it might not be terminal.
____________________
'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[Weisse Schlange]

Common faults are TPS and icv issues
Best resolved with a secondhand complete throttle body.

Best way to figure it out is spray easy start in the air intake udwrbthe seat and as of it runs.
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Hing Oan