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!

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!

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! 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.

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!