Starting the bike instantly kills battery

Hi all,

I've got a 2013 WR250R with about 38,000kms on it. I've had it for a couple of years now, and the only issue I've had is the battery randomly dying on me three times. Initially, I just thought it was a dead battery, so I replaced it and away I went for another year. Then it happened again, this time, before replacing the battery I checked the regulator and stator to ensure the bike was charging effectively. The resistance values and voltage readouts seemed to be close or within spec.
After about a month on the 3rd brand new battery, it died again, however the circumstances were very strange.

The bike started fine (cranked quickly), I stopped it and started it 4 more times throughout my ride, each time it cranked equally as fast, and on the 5th time starting it, the start motor clicked but absolutely no cranking and the dash lights dimmed to almost off. I then tried starting it again and the same thing happened.
So then I tried roll starting it, however, once it was started it was spluttering and wouldn't run for longer than a minute or so.
I checked the voltage on the battery and it was 10.2 V (DEAD). I replaced the battery with an older one and the bike started and ran fine, and it has been running fine for the last week.

TL;DR. There seems to be something on the bike that is causing it to drain a HUGE amount of current when starting resulting in a dead battery, this only seems to occur at completely random intervals. The charging system seems to be working fine.

Where should I start in terms of diagnosing this? Starter motor wiring perhaps?

Has the stator recall been completed? If you're not sure, check with your local Yamaha dealer to see if there is a record for this VIN.

johnkol wrote:

Has the stator recall been completed? If you're not sure, check with your local Yamaha dealer to see if there is a record for this VIN.

Yes, according to the previous owner it has. I will double-check with the dealer tomorrow though. Thanks

If the stator recall has been completed and you checked the stator and R/R as shown on Page 8-76, then it's probably an intermittent problem that will require swapping out parts.

anything that can keep the starter engaged after the start would be my first suspicion. if the engine starts and the starter stays on you won't notice unless you are looking for it. the Sprague clutch in the starter drive lets the starter turn without making any noise when the engine is running. the clutch is a set of oval shaped rollers that lock up in one direction (when the starter is faster than the crankshaft) and then slip in the other direction (when the crank turns faster than the starter). one way to see if this is happening would be to use a meter on the starter. when the starter is engaged you will read 12ish volts (maybe even as low as 10), when the start button is released there should be zero volts on the starter terminal. you will have to test it every start until you are satisfied one way or another. start switch and starter relay(s) would be the prime suspects if the motor stays on... they are the controls. left on, the motor will simply stay running until it burns up

the starter is a huge energy suck under normal circumstances. a starter with no load is even bigger

johnkol wrote:

If the stator recall has been completed and you checked the stator and R/R as shown on Page 8-76, then it's probably an intermittent problem that will require swapping out parts.

Called the dealer, and the recall has definitely been done. I will check the stator and R/R again to be sure, but the last time I checked they were all good.

dogmeat wrote:

One way to see if this is happening would be to use a meter on the starter. when the starter is engaged you will read 12ish volts (maybe even as low as 10), when the start button is released there should be zero volts on the starter terminal.

I don't think the starter was staying on, but i'll chuck a meter on and check what you said.

I pulled the starter motor apart on the weekend and gave everything a good clean. The brushes were still within Spec according to the manual. After cleaning everything and polishing up the commutator with some emmery tape, the starter motor is now a lot louder (more high pitched), but sounds healthy. Haven't had an issue just yet, however, I've only started it a handful of times.
I guess time will tell.

wrr-karl wrote:

Called the dealer, and the recall has definitely been done. I will check the stator and R/R again to be sure, but the last time I checked they were all good.

It might be that the problem is intermittent and static measurements won't capture that. You can install a voltmeter/USB outlet and monitor the voltage while you're riding to get a better idea of what might be going on.

johnkol wrote:

wrr-karl wrote:

Called the dealer, and the recall has definitely been done. I will check the stator and R/R again to be sure, but the last time I checked they were all good.

It might be that the problem is intermittent and static measurements won't capture that. You can install a voltmeter/USB outlet and monitor the voltage while you're riding to get a better idea of what might be going on.

Yeah, that's a good point. Having a voltmeter would be quite handy.
Thanks for the tips.

Another thing to check would be the wiring; maybe a wire has been stripped a tiny amount and makes random contact with the frame.