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Brad Fitzpatrick

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Motorcycle won't start -- alternator? battery? [Sep. 6th, 2007|10:39 pm]
Brad Fitzpatrick
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My motorcycle (BMW F650GS) won't start.

-- turn the key, no lights (maybe I left it on?)
-- if I jump it from my car, it'll turn on, and engine will start
-- once I disconnect jumper cables, engine dies

It's that last point which confuses me: once it's going (and I left it run 5+ minutes), why does it need the battery anymore? I don't see why disconnecting the battery immediately kills the engine.

Any suggestions?

[User Picture]From: avatraxiom
2007-09-07 05:50 am (UTC)
I had something similar happen with a car of mine once--as I recall the problem was that the battery terminals and connectors were corroded to the point that a jump would work but the normal flow of electricity didn't.

Your motorcycle is so new that I can't imagine that's the case, though.

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[User Picture]From: scosol
2007-09-08 12:57 am (UTC)
What he said-

Sure it *could* be the alternator as all others say, but I doubt that would die so quickly on such a new bike.
Also, "battery too dead to for engine to run" is BS too- the alternator can provide *plenty* of energy for a spark.
But the one thing it needs is an actual complete circuit.
So I would check the battery terminal connectors for looseness, as well as the charging wire from the battery + on the alternator.

The other thought is that you might have a SERIOUS short, that drained the battery and will also kill all electrics in the way you describe- think "large wire disconnected and hitting frame"
If you don't find an obvious loose or dis-connection take that bitch back to the dealer.
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[User Picture]From: maxvt
2007-09-08 05:18 pm (UTC)
Happened to my car, too. Bad connection at the battery -> 1.5 volts difference between alternator and battery terminals -> battery wouldn't charge properly, leading to starting issues, although I did go to the garage before the car stopped starting at all.
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[User Picture]From: xaosenkosmos
2007-09-07 05:52 am (UTC)
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[User Picture]From: girl_on_a_stick
2007-09-07 05:58 am (UTC)
Could be:
Bad Batter
Alternator troubles
Rectifier troubles (this is my guess)
Battery leads need cleaning
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[User Picture]From: girl_on_a_stick
2007-09-07 06:02 am (UTC)
Hmm more I think about this the more I lean towards it being just a way dead battery.

I highly recommend buying a trickle charger, for just this sort of occasion. Good thing to have around. You can get them at any motorcycle store for around $50.
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[User Picture]From: brad
2007-09-07 08:46 am (UTC)
Trickle charger: right! ... I remember others recommending those. I'll pick one up, thanks!
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[User Picture]From: travisd
2007-09-07 12:27 pm (UTC)
Specifically, a Battery Tender. Something that's has some smarts and won't cook the battery.
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[User Picture]From: glyphard
2007-09-07 01:04 pm (UTC)
yes, it's(trickle charger) the only way to get a battery to last, if you don't ride nearly every day. Now you know empirically, that it's a necessity.

It confuses me too, but even old motorcycles are the same way:

battery totally dead == bike won't run.

Plus, even if it is the alternator, a new battery is a lot cheaper and easier to rule out than an alternator.

Could be the headlight that's always on. Could be the little bit of power that runs the tiny instrument cluster...

Good luck.
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[User Picture]From: matthew
2007-09-07 03:24 pm (UTC)
Get the BMW one... the battery in my bike is a gel cell and takes a little extra care to charge. I'm not sure about what they put in the F650 but I wouldn't be surprised if it were a gel cell.

Also, call your dealer, this is warranty work :)
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[User Picture]From: bloonail
2007-09-07 08:36 pm (UTC)
I should read to the bottom to find out if it started... but its probably not in need of a trickle charger. The problem is that the motorcycle is not generating power on its own. If it were creating current it would run once it was off cables. If the battery is dead it would still run, but rough until the battery charged. Its likely the alternator, and some type of cutoff that won't let your BMW start unless its above some basic charge level.
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[User Picture]From: chris
2007-09-07 09:42 pm (UTC)
this would have been my guess as well.
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[User Picture]From: furrr
2007-09-07 06:34 am (UTC)
i think it might be the alternator
if it's inoperable, the only source your motorcycle feeds on is the battery, and given the small capacity of the battery, unlike one in a car, it should run out pretty quickly.
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[User Picture]From: silona
2007-09-07 06:50 am (UTC)
um ditto on alternator...
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From: seeds_of_peace
2007-09-07 06:59 am (UTC)
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[User Picture]From: mobley
2007-09-07 12:01 pm (UTC)
fourths on the alternator. if the alternator is dead, the motorcycle needs electricity from the battery.
i've had too many crap cars that this has happened to.
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[User Picture]From: krow
2007-09-07 07:30 am (UTC)
It is the alternator. The jump is recharging the battery ever so slightly and giving you enough juice for the plugs to fire. Just hook up a multi-meter to the alternator and see if it is producing any juice. While you are add it, check the cables from it to the engine (especially the ground if it has one) and make sure they are intact.
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[User Picture]From: deemon
2007-09-07 08:35 am (UTC)
Only very few old cars (except diesel ones) can run without battery. My grandfather's GAZ M-20 Pobeda certainly could, but I haven't seen any other examples. Same with motorcycles, I suppose.
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From: brianlmoon
2007-09-07 01:46 pm (UTC)

It is a charging issue

From growing up around motorcycles, I can tell you that it is a charging issue. Now, exactly what I don't know. But, the battery is probably fine. Take it to a shop. They should be able to diagnose it quite easily.
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[User Picture]From: daberna
2007-09-07 02:45 pm (UTC)
Your bike seems too new for it to be an alternator problem, but I agree with the others that it seems like the most likely cause. Isn't the bike under warranty? I guess it's a pain to take a bike in your can't ride.
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[User Picture]From: zarex
2007-09-07 03:20 pm (UTC)
It's related to the alternator, as others have said, but it's probably not the alternator itself. It's more likely to be the voltage regulator or related intermediate circuitry that feeds energy from the alt to the battery (and the rest of the bike).

That, or a connector fell off. That's the most common problem with a newer bike.
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[User Picture]From: bitwise
2007-09-07 08:28 pm (UTC)
The battery does act as a nice fat capacitor, smoothing out the nasty jagged voltage coming from the alternator/generator. If the battery or battery cables are shot, the noisy voltage can cause electronics to malfunction.
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From: (Anonymous)
2007-09-07 10:56 pm (UTC)

Motorcycle won't start

Call Grandpa
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From: (Anonymous)
2007-11-02 05:22 pm (UTC)

Dead Battery

Brad I just had the same problem with my suzuki GS500. My Battery was totally flat 0v.I tested the alternator and the regulator with a friend's battery and both worked fine. I spoke to a mechanic who could not explain to me why is that you need a battery to make the motorcycle run. I thought you could disconnect the battery and the alternator would provide the current needed to keep the bike going. Does anyone have any idea why is that so? My old Honda CB400 1981 used to run without any battery. So did my Beetle 1980.? Can anyone explain this?
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From: (Anonymous)
2008-05-28 12:33 am (UTC)
wow, same problem with my 78 kz400, did you figure it out? I could use a tip.
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