Author Topic: Suzuki GS650 voltage drops to 8V. Won't start.  (Read 44 times)

Offline steviewilson87

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Suzuki GS650 voltage drops to 8V. Won't start.
« on: May 17, 2018, 11:47:00 PM »
Had an intermittent fault with my 1981 Suzuki GS 650 that's now became a bit of an issue..... The f****r won't start anymore!
 It cranks fine & the battery is holding a charge. Spark is pretty weak (swapped plugs for new). Battery drops to 8V when starting, back to 12V when releasing start. Checked coils & getting 4.5ohms & 13kOhm primary/secondary sides. I'm thinking short to earth, but wondering if anyone has any ideas? Cheers!

Offline R

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Re: Suzuki GS650 voltage drops to 8V. Won't start.
« Reply #1 on: May 18, 2018, 03:16:43 AM »
I've had a battery that had those exact symptoms.
It wasn't long for this earth after that....

Can you try boosting the battery by jumper leads, say from a car.
This would say for sure if its just a low battery, or if you really do have a problem.
Be ready for a quick disconnect of the hot lead from the boost battery...

btw, you say your battery "returns to 12v".
12 point how many volts, precisely ?
A battery at 12.0 volts only is already rather dead...
hopethishelps.

Offline Rex

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Re: Suzuki GS650 voltage drops to 8V. Won't start.
« Reply #2 on: May 18, 2018, 10:04:22 AM »
The battery's had it. Jump lead it from your car to prove.

Offline steviewilson87

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Re: Suzuki GS650 voltage drops to 8V. Won't start.
« Reply #3 on: May 18, 2018, 11:35:12 AM »
Sorry, I've already proved its not the battery. I connected my car battery straight to the motorbike battery tails, and it was still immediately dropping to 8V & cranking like crazy.

Its got progressively worse (had the bike a month!). Started fine, then took a bit of effort, now won't start. Battery sits about 12.5V.

Offline Rex

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Re: Suzuki GS650 voltage drops to 8V. Won't start.
« Reply #4 on: May 18, 2018, 11:45:31 AM »
Does "cranking like crazy" mean it was turning over at the correct speed on the starter?
Measuring 12.5V doesn't really mean a great deal; take a dead battery out of your car and you can still get 12V on a voltmeter but it's still knackered and won't turn the car over. "Surface charge" and all that...

Offline steviewilson87

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Re: Suzuki GS650 voltage drops to 8V. Won't start.
« Reply #5 on: May 18, 2018, 11:58:39 AM »
New to bike mechanics to still trying to figure it all out. It was turning over a lot quicker with the car battery than it normally would. I could borrow a load tester and test it. I'm guessing cranking too quickly would make a difference? Thinking checking the air filter too? New plugs have done maybe 150 miles & they're black at the electrode. Cheers for your help

Offline R

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Re: Suzuki GS650 voltage drops to 8V. Won't start.
« Reply #6 on: May 18, 2018, 11:36:07 PM »
Where are you measuring this 8v at then ?
For a good car battery to drop that low, the jumper leads should be glowing red
and smoke would be coming out of something.

Cranking like crazy sounds - well, crazy.
Can you remove the starter for a look at its insides, to see they are intact and good.
Has the bike lost all compression for it to do that ?

This doesn't bode well....