Greetings all - how's your YBR125 knowledge?

[Uncle Pete]

Hi everyone. Pete in Liverpool. First post, so please be kind.

 

I come seeking advice. I have a 2009 YBR125 which I've had since a year old. It has been very kind to me, though I don't ride very often and - don't judge me! - it currently has 4,300 miles on the clock. That can make it a bit of a paradox as in some respects it's quite elderly and in others it's barely run in.

 

This bike has been absolutely bullet proof. The starter motor has never cranked for more than three seconds continuously and it's never failed an MOT. The only things I've had to throw at it are fuel, oil and a bit of paint on the swinging arm and if you opened the valve on the front tyre you'd probably get some Japanese air. And so onto the problem. It's started randomly and frequently cutting out. The problem first manifested when coming to a stop at lights, when it would conk. Since then it's grown so that it will sit stationary for a couple of minutes or so with a stable idle at around 1,500rpm and then just cut out. It will now also cut out when riding, which makes the whole thing a bit of a buckaroo experience.

 

As I said, I've not had to touch this mechanically in 14 years until now so I don't know a lot about it, and in truth I'm probably better on cars. I'm also finding information about the fuel injected models quite hard to find online.

 

I've had a look this morning to see what I can spot and if you can be bothered reading I'll share some of my prelimenary thoughts. Trying to work the systems out, it looks like the induction draws from external and an inlet under the seat. This passes through the air filter and into the throttle body. It looks like the throttle body has a cable operated primary and what seems to be a stepper motor on the top which suggests that there's an auxiliary air control valve there. That seems to have an adjustment screw on it which might adjust idle, but the idle speed seems fine so I haven't touched it. The throttle body then passes into a short inlet manifold which looks like it's got the fuel injector mounted in it. It must have an oxygen or mass air flow sensor somewhere in that chain, but I haven't pegged that yet. There's a crankcase ventilation pipe which presumably must have a PCV and surprisingly there seems to be some kind of exhaust gas recirculation system. It seems surprisingly sophisticated for such a small engine, but it's worked brilliantly, so no complaints. On the ignition side, I've not had the tank off, but there's a box with heat sink vents under the left hand side of the tank. I don't know if that's an ECU, a capacitive discharge unit or even a seemingly very big coil pack.

 

Still with me? Thanks. So my first thoughts were a dodgy auxiliary air control valve, but it still conks with the main throttle plate open, so I've discounted that. I've run it with the air filter out and the problem is unchanged. When it runs, it runs clean, so I've dismissed, maybe prematurely, crud in the injector. I've replaced the battery with an identical spec and cleaned the primary contacts with contact cleaner. The lights seem to remain stable and steady throughout. I've checked all the easily visible connections for tightness, but my gut feeling is it's probably electrical. I'm denied most of the basic diagnostics as it's an intermittent fault. I know if I check for spark I'll get one and if I check for fuel I'll get it. So often in this situation it just turns into the sequentially replacing parts game which is frustrating and expensive.

 

What's your thoughts? I'd rather not replace a full ignition system to find out it was a dodgy kick stand switch, so has anyone encountered this sort of behaviour before in a YBR and found a solution? Any advice is warmly appreciated.

 

=====================================================

 

Solution

 

A new spark plug sorted the problem completely. A salutary lesson in basic servicing!

Edited November 16, 2024 by Uncle Pete
Solution added

[Nick the wanderer]

Hi, welcome to the forum.

With a random fault like this I'd be looking at the simplest things first, funny you should mention the side stand switch, but that's where I'd start on the electric side. Sounds like a short somewhere. Check all your connections, unplugging and cleaning, plus the kill switch on the bars, that sort of thing.

 

[Simon Davey]

It could just be the spark plug, does it only conk out once at running temp? . 

[Uncle Pete]

1 hour ago, Nick the wanderer said:

Hi, welcome to the forum.

With a random fault like this I'd be looking at the simplest things first, funny you should mention the side stand switch, but that's where I'd start on the electric side. Sounds like a short somewhere. Check all your connections, unplugging and cleaning, plus the kill switch on the bars, that sort of thing.

 

 

Yeah...good shout. I've checked that the plugs are all in but unplugging and replugging absolutely everything would probably be a good thing to do. Thanks!

 

1 hour ago, Simon Davey said:

It could just be the spark plug, does it only conk out once at running temp? . 

 

It's a fair point as it's still on the original plug, but no, the problem persists both hot and cold. After fifteen years it probably deserves a new plug.

[RideWithStyles]

On 09/11/2024 at 11:49, Uncle Pete said:

Hi everyone. Pete in Liverpool. First post, so please be kind.

 

 

I come seeking advice. I have a 2009 YBR125 which I've had since a year old. It has been very kind to me, though I don't ride very often and - don't judge me! - it currently has 4,300 miles on the clock. That can make it a bit of a paradox as in some respects it's quite elderly and in others it's barely run in.

Hi and will be i have the same thing a old bike but few miles, joys is most problems would will be more common knowledge now!

 

This bike has been absolutely bullet proof. The starter motor has never cranked for more than three seconds continuously and it's never failed an MOT. The only things I've had to throw at it are fuel, oil and a bit of paint on the swinging arm and if you opened the valve on the front tyre you'd probably get some Japanese air. And so onto the problem. It's started randomly and frequently cutting out. The problem first manifested when coming to a stop at lights, when it would conk. Since then it's grown so that it will sit stationary for a couple of minutes or so with a stable idle at around 1,500rpm and then just cut out. It will now also cut out when riding, which makes the whole thing a bit of a buckaroo experience.

sound more electric based rather than pure mechanical one…

 

As I said, I've not had to touch this mechanically in 14 years until now so I don't know a lot about it, and in truth I'm probably better on cars. I'm also finding information about the fuel injected models quite hard to find online.

Yep pain it is. 
 

I've had a look this morning to see what I can spot and if you can be bothered reading I'll share some of my prelimenary thoughts. Trying to work the systems out, it looks like the induction draws from external and an inlet under the seat. This passes through the air filter and into the throttle body.
air induction common back then for most bikes.

It looks like the throttle body has a cable operated primary and what seems to be a stepper motor on the top which suggests that there's an auxiliary air control valve there.
cable throttle is your hand grip control is the upper valve control of the carb/injection but the ecu has the prime command valve of the lower one so it has overlord control over anything you ask…it determines what it gets, your actions are merely a suggestion. If that makes sense.

That seems to have an adjustment screw on it which might adjust idle, but the idle speed seems fine so I haven't touched it.

Yes only touch this if the carbs/injection is balanced and it’s too high or too low when up to heat at idle.

The throttle body then passes into a short inlet manifold which looks like it's got the fuel injector mounted in it. It must have an oxygen or mass air flow sensor somewhere in that chain,

oxygen sensor is in the airbox and exhaust most of the time in these aged engines, more advanced injections and ecu got proper maf.

ut I haven't pegged that yet. There's a crankcase ventilation pipe which presumably must have a PCV and surprisingly there seems to be some kind of exhaust gas recirculation system.
Yes more commonly known as a PAIR system, if your a Suzuki owner.

It seems surprisingly sophisticated for such a small engine, but it's worked brilliantly, so no complaints. On the ignition side, I've not had the tank off, but there's a box with heat sink vents under the left hand side of the tank. More than likely it’s either the regulator (if your a Honda boi you’ll get to know this very well) I don't know if that's an ECU, a capacitive discharge unit or even a seemingly very big coil pack. That’s for the charging system.

 

Still with me? Thanks. So my first thoughts were a dodgy auxiliary air control valve, but it still conks with the main throttle plate open, so I've discounted that. I've run it with the air filter out and the problem is unchanged. When it runs, it runs clean, so I've dismissed, maybe prematurely, crud in the injector.

if it’s a slow death/stop (so one or more sec) it’s more fuel issues, if very quick (less) and sudden its more likely electricial. 

 

I've replaced the battery with an identical spec and cleaned the primary contacts with contact cleaner. The lights seem to remain stable and steady throughout.

The lights should get slightly brighter if you rev it abit at idle if not your charging system is suspect reg or stator or wiring.

I've checked all the easily visible connections for tightness, but my gut feeling is it's probably electrical.

Yep my first thought.

I'm denied most of the basic diagnostics as it's an intermittent fault. I know if I check for spark I'll get one and if I check for fuel I'll get it. So often in this situation it just turns into the sequentially replacing parts game which is frustrating and expensive.

 

What's your thoughts? I'd rather not replace a full ignition system to find out it was a dodgy kick stand switch, so has anyone encountered this sort of behaviour before in a YBR and found a solution? Any advice is warmly appreciated.

remotly a dodgy side stand switch or wires (more like the wires) could do it, But id say if it was regular it would be when bumps or a certain rev to harmonise or shake it to do it but your problem is a bit more random and at a stop, sounds progressively getting worse/frequent?
i wouldnt just change a full system just like that, not thinking just a single spark weak or not or pack would totally stop a bike but your bike is a single cylinder that doesn’t run particularly poorly at any point, if its does both cold and hot cut outs it’s less likely resistant build up in the wires on a simple and assume a well conditioned machine.
What might be good and cheap is if you bike has an diagnostic port and get a cheap reader, might give you a clue? There is a possibility of two slightly different problems thats its bounces between but you only see it as one- it’s unlikely but if you get one sorted dont alway think its done or it wasn’t what you just did fix wasnt the problem.check those things out and come back.

Yeah you could change the spark plug? Its only one and They are very cheap, the plug uses the engine as a ground point to spark too, is the inner threads of the case poor? Is the plug cap bad?

 

[Uncle Pete]

Thanks for the input! It absolutely hadn't occured to me that the bike would have an OBD port but that makes a lot of sense. I'll have a poke round at the weekend and maybe get the tank off to see what the ECU offers in terms of connectivity. I've got an OBDII reader but I don't know if bikes use the same interface port. Likely not I'd guess as it's massive, but I'll explore further. In the meantime I'll order up a plug as well.

 

Thanks lots!

[Uncle Pete]

Well, it's time for a hat tip to Simon who nailed the diagnosis, and a big thanks to RideWithStyles for giving me the kick up the arse to go back to basics.

 

Put a new plug in and she's smoother than the cream on the proverbial Twinkie. Problem solved.

 

Thanks guys!

Edited November 16, 2024 by Uncle Pete

[Simon Davey]

3 minutes ago, Uncle Pete said:

Well, it's time for a hat tip to Simon who nailed the diagnosis, 

Blimey, that's a first

 

Good news Pete, thanks for the update.