Starter Motor Woes

[DrBeardface]

I have a 2007 WR450 and I've been fighting a losing battle with the starter. Old one gave out so I put a new one on Saturday morning--thing cranked over no problem. Tuning is off so it didn't want to start and when it did it only ran for a short time...separate issue.

One time it started and idled for about 10 seconds then died, and when I go to start it again the motor is really laboring and not turning anywhere near fast enough to start the engine. It is even laboring when the spark plug is out and there's no compression. Does anybody have any ideas what could be causing this?

Thanks!

[MANIAC998]

Does it kick over easily? Perhaps something is wrong inside the engine, like the crank or top-end bearing.

Maniac

[DrBeardface]

Does it kick over easily? Perhaps something is wrong inside the engine, like the crank or top-end bearing.

Maniac

See, I don't know if it kicks over easily. The motor is in something else and the kick start isn't on it anymore so electric start is all I got. There has been zero run time since the last time it was apart to get a new piston and cylinder and everything *seemed* like it was fine then. It does seem like something could be going on inside though, I'm just hoping for a cheaper fix lol. I'm completely baffled at this point...

[Mbirt]

Is this an FSAE application? Our EFI system electrical loads are really too much for the stock WR450f charging system. Combine that with all the cranking that goes into tuning a standalone EFI from scratch (with huge plenum volume, no less) and a starter that is barely strong enough for the stock application, and bad things happen quickly. I've killed two stock 2011 WR450 armatures in this 2012 season of calibration and competing.

I suggest checking the voltage drop at the battery during a successful cold start and comparing it to a failed hot start when the motor stops turning. But don't keep your finger on the start button for long once the starter motor stops turning. That'll burn the epoxy off the windings in a hurry. If the voltage is below 12.5v before the hot start, give the battery a quick charge and try starting again before the engine and starter motor cool. That should help you determine whether or not you should be suspect of the starter motor, the battery, or something else.

[DrBeardface]

Is this an FSAE application? Our EFI system electrical loads are really too much for the stock WR450f charging system. Combine that with all the cranking that goes into tuning a standalone EFI from scratch (with huge plenum volume, no less) and a starter that is barely strong enough for the stock application, and bad things happen quickly. I've killed two stock 2011 WR450 armatures in this 2012 season of calibration and competing.

I suggest checking the voltage drop at the battery during a successful cold start and comparing it to a failed hot start when the motor stops turning. But don't keep your finger on the start button for long once the starter motor stops turning. That'll burn the epoxy off the windings in a hurry. If the voltage is below 12.5v before the hot start, give the battery a quick charge and try starting again before the engine and starter motor cool. That should help you determine whether or not you should be suspect of the starter motor, the battery, or something else.

That's exactly what it's for, and I have a large box full of burnt out starter parts proving your point lol. What I don't get is that I was able to tune a 2003 WR450 engine from complete scratch a month ago and didn't go through a single starter motor, but this motor was literally pulled out of its box from Yamaha 9am Saturday morning and by 10am it was doing this. I kept the tune from the 2003 engine thinking it would be close enough to get it at least started with less cranking.

This is all while hooked up to the engine dyno and with the battery plugged into a charger. Voltage starts around 13.5 and drops to 12.0 while cranking so that all seems fine. The engine never even ran long enough to get hot so this is all while cold.

I just don't get why the starter would go out this quickly, it was not cranking for any absurd period of time and it worked perfectly fine until after that one time the engine started. If it had gone through a few weeks of tuning, sure, but less than an hour?