Ongoing Charging/weak spark problem 83xs650

Stumpedchump

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Hi all. It's an 83 xs650 with 13k on it.

I've had an issue with this bike since I got it. When I first bought it, it didn't run. needed a new battery and the stator was fried. Replaced them both and have been riding it since though whenever I come to a stop after it's been warmed up it will often backfire through either carb it seems and sometimes die. I can keep it running by feathering the throttle.

It has weak spark. Doesn't look healthy and won't arc beyond the span of a plug electrode. Also, plugs look carbon fouled after a bit. I've narrowed it down to a poor charging circuit at low rpms.(I think anyways)

What I've done. Replaced the stator and the battery when I first got the bike. Since then, coil ohm tested a little out of spec. replaced, no change. Obviously replaced plugs and wires/caps. I've done the magnetic test against the stator cover. Ign on will pull a wrench against it. Tested the 3 legs of the stator. each one shows around 6 ac volts at 1200 rpm. I believe they're supposed to be between 10-11 ac volts. Ohm test between the three legs, checks out ok exactly where it should be. Ohm tested across the rotor brush surfaces, 5.2ohms. Looks ok. Replaced brushes, no change. Have battery voltage at one brush and ground at the other as it should.

I'm stumped. Any help would be great.
 
All these charge poorly at low RPMs. That's when the battery kicks in and supplies the ignition with the voltage it needs to operate properly. That's why a good battery is required on these. You need to determine if you do indeed have a charging problem. Do the simple charging output test. Clip a volt meter to the battery and test it's voltage at idle and then at 3 to 3.5K RPMs. You should see around 12 at idle, maybe a bit more or less, and around 14 when revved. If your charging output is good then the next question is whether or not all that voltage is reaching where it needs to go.

This can be a common problem on old bikes, low voltage to the coils. You start out with 12 volts at the battery but by the time it goes through all the wiring connections and switches, it may be less. You could be getting only 9 or 10 volts at the coil and ignition black box. That will spark the coil but it will be weak. It can also make the black box act up and malfunction. So, do some voltage tests at the fuse block. The main fuse shouldn't be a problem as it is a direct feed on a short wire from the battery. The other 3 auxiliary fuses may be though. Their power feed passes through the ignition switch and in the case of the coil and black box, through the kill switch too. If those components are dirty or corroded up inside, you may see a voltage drop.
 
Hi 'chump and welcome,
what 5T sez, clean every single last electrical switch and connection on the entire machine.
Couple of points from your posts:-
the stock coil has the wires cast into it so the dreaded PO must have fitted an aftermarket coil with separate wires but was it the right one and was your own replacement same as his or to the recommended spec?
And your replacement fuses should be a 20Amp & three 10 Amps not all 10Amp.
And my no multimeter needed quick and dirty charging test:-
Point the headlight at a wall and rev up. If the light brightens with revs, it's charging. If it don't, it ain't.
 
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Thanks for the responses.

fredington, I replaced the coil with a good known used coild and replaced the caps at the plug side. It is for sure good. And I'm not basing my conclusion on my charging circuit being an issue based on the voltage at the battery but more at the Curly's stator ac voltage test. As it shows in Curly's test, I should have between 10 and 11 ac volts at idle on any and all 3 legs of the white stator wires. I only have 6. Also, there were only 3 10 amp bus fuses in the box. There wasn't a 20 amp fused circuit in there. Doesn't appear to have been tampered with. Is it possiblt that circuit was changed on the 83 models? I've been having a tough time finding schematics for my year specifically.

5twins, I will check the voltage at the coils and repost after I have some numbers. Thank you
 
I have battery voltage at the coil at ignition on. Within a tenth of a volt.

Doesn't the stator test seem concerning? I figured at only half the output it's supposed to be throwing that was for sure my problem?
 
Thanks for the responses. - - - Also, there were only 3 10 amp bus fuses in the box. There wasn't a 20 amp fused circuit in there. Doesn't appear to have been tampered with. Is it possiblt that circuit was changed on the 83 models? I've been having a tough time finding schematics for my year specifically. - - -

Hi 'chump,
all XS650s after the early XS650E had the same fusebox. Late XS650Es and later models all left the factory with a flat plastic box atop the battery that had four glass tube fuses in it. Certainly my '84 Heritage Special (essentially the same bike as your '83) came with one.
One fuse was a 20Amp that fed power to the ignition switch, the other three fuses were 10Amps that were fed power back from the ignition switch when the key was turned on and protected the bike's different wiring circuits.
You can see a photo of the stock glass tube fusebox in MikesXS on-line catalog.
It is commonly held that most POs wear ball caps to hide their circumcision scars so who knows what your bike's PO has done?
 
Hi 'chump,
all XS650s after the early XS650E had the same fusebox. Late XS650Es and later models all left the factory with a flat plastic box atop the battery that had four glass tube fuses in it. Certainly my '84 Heritage Special (essentially the same bike as your '83) came with one.
One fuse was a 20Amp that fed power to the ignition switch, the other three fuses were 10Amps that were fed power back from the ignition switch when the key was turned on and protected the bike's different wiring circuits.
You can see a photo of the stock glass tube fusebox in MikesXS on-line catalog.
It is commonly held that most POs wear ball caps to hide their circumcision scars so who knows what your bike's PO has done?

Well, I suppose I should find that circuit and go ahead and throw an inline 20 amp fuse in there. Thanks for the heads up.
 
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