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Hi just looking for some advice on why my engine isn't running. It cut out down the A1 at about 75mph. I got it jump started twice but cut out after a few seconds and then the dash started going off when I pressed the starter. All fuses are good and all plugs underneath the tank are in intact and the battery is good. I'm 99.9% sure it's an electrical issue but just don't know where to start. There's no error codes, Are they any sensors that I should check? Any advice would be greatly appreciated.
 

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2008 YZF-R125 (180cc)
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552 Posts
electrical stuff is a bit of a tricky one, mainly because there doesnt really seem to be an "easy way" of diagnosing stuff (that I've found anyway). You just have to get your multimeter and start following wires, chickeing plugs, contacts and voltages.

That said I do think there's a couple of thigns which can make the bike cut out.. I'm havin got go by hearsay since these aren't connected on my bike so can't attest exactly to their behaviour...

- the stand switch - not sure what it's supposed to do bc mine has never worked but i think it stops you starting the bike when on the stand? I've head things before about people's bikes cutting out and it was just the stand bouncing around and slightly engaging the stand switch whilst riding causing cutouts. Like I say, can't confirm or deny bc mine never worked but could be worth checking.

- behind the sprocket cover, just a wee bit down from the sprocket itself is a sensor which pushes onto a sort of "nubbin" (the wire runs thru all the skank behind the sprocket..mucky area). I thought it was for oil temp but apparently it's for the neutral switch (which makes more sense tbh) - but allegedly it may have the main ecu power connected to it too (I have not substantiated this but someone I was chatting to had a similar issue to you) - so that coud be worth checking. If that connector is wobbly (which it tends to become over time) and if it IS related to the ECU then you might get the sort of behaviour you're describing too. You can use some thin nosed pliers to gently tighten/re-shape the connector so it clips on snugly It'll make more sense when you see it.

- there's also a 2-pin cable that goes into the clutch lever assembly which I think is there to prevent you starting the bike in gear without the clutch held in. Again i don't really see how that would be a problem but it might be something to check. You can bypass that swtich just by shorting the two contacts of the plug that goes into the clutch lever (e.g. paperclip). I have a 1-finger clutch lever on mine so had to short that connector or it wouldn't start.

- is your fuel pump running consistently? a pump on the way out might also give you random cut-outs. The first time my pump went sometiems it would start, sometimes not. If it were to cut out at speed you probably wouldnt be thinking about checking whether there's the hum from the fuel pump

Any of those which had a dodgy connection could potentially cause or contribute to what you're seeing.

Other than that - all your ignition wiring is basically just below the fuel tank (red plug from that bundle), generally easiest to take the tank off to have a look - you can get some wet in there but kinda unlikely that it would work at all if so, but that's where most of your wires go so you might end up there. There's also a good chunk of wiring inside the right shoulder panel (just below the front fairing, follow from the ignition wiring) - though that's mostly cables for headlights, speedo and instruments and the plugs are fairly waterproof and somewhat protected.. so again probably not your area.

I'm sure you've probably done this but I'd also check the battery voltage when running and not. When running it should be abour 13.6v, and not running it should be roughly in the 11.6-12.3 sorta range depending on state of the battery and how freshly charged it is. Battery with a dead cell or something could also potentially contribute to unexplained weirdness.


Hope that helps :)
 

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Yamaha R125 2009 (2018 look)
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same problem happened to me, it was a dead battery. yours might be faulty and showing you its good but maybe it is not you know?
 
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