Erratic voltage *** Solved bad coil

[bpupeza]

When I check voltage with the bike running my multi-meter goes berserk! It goes from single digits up to 20 or 30 back and fourth and its barely readable. I tried another meter with similar results.
This motor was in my other xs and charging fine before I swapped it into my 73. It is a 78 motor and charging system with points and separate reg/rec. It has a new wire harness. I disconnected all of the lights, horn, and brake switch. I bypassed the kill and the key switch. I swapped batteries, regulator, and rectifier with different ones.
I disconnected the the regulator, rectifier, and stater and it still did the exact same thing.
It seems that all that's left is the points condenser, and coils.
It fires up and runs good.
I did the slap test. Its nice and strong. I have 11.4 volts and the brush.
.7 between the white wires on the stater. No continuity from whites to ground.
5.7 ohms between the slip rings. No continuity to ground with the brushes removed.
I cleaned my grounds
I cleaned the key switch.
when I try to check AC volts I get the same erratic readings.
I ran a jumper from the battery to the brush with the same result.
Any thoughts?

 

[Jan_P]

Hi
I would suspect the Regulator is connected wrong and they are sensitive for that if electronic.
There is mention of a New harness .. I would check the schematic.
There are a different charging wiring pre 1980 and past 1980
So if the harness is for a past 1980 and goes into an earlier bike it might go wrong
And compare colors and where the wires go.
Pictures and what parts what harness are installed posted here makes it simpler.
Here in this forum is a description to be found of differences in charging circuit.

 

[bpupeza]

Hi
I would suspect the Regulator is connected wrong and they are sensitive for that if electronic.
There is mention of a New harness .. I would check the schematic.
There are a different charging wiring pre 1980 and past 1980
So if the harness is for a past 1980 and goes into an earlier bike it might go wrong
And compare colors and where the wires go.
Pictures and what parts what harness are installed posted here makes it simpler.
Here in this forum is a description to be found of differences in charging circuit.

I bought the harness from mikes xs. It is for xs2 and tx650. Not all of the wire colors match the diagram and they could not provide a cross reference. I also included a pic of the other regulators (vr115) and rectifiers that I tried using.
This morning I tried a spare stator that I have with the same outcome.

 

[Jan_P]

Ok I got the pictures I dont have time right now
Perhaps tonight or tomorrow
But at the pictures I can see the Stock regulator.
It has bad reputation but it has the advantage that it is possible to find faults on it.
So I would recommend to keep that one there for the moment
Or more exactly take it out and test and inspect.It on the work bench
Soldering and the backside opposite of the picture.
And do some testing on it so it is within specs
Please do the fault finding procedures ( if it is another year model please google it )

https://thexscafedotcom.files.wordp...ha-service-manual-1970-1974-pages-101-150.pdf

And see if it is right
I shall look more and think later

 

[bpupeza]

This is a very nice troubleshooting guide. I will work through it step by step and respond when I am done.
I don’t have alligator clip test probes for my meter, which is required, so I will have to get some.
Thank you very much for your response.

 

[bpupeza]

Problem solved. A bad coil was grounding out and causing the big voltage spikes.
I disconnected the charging system and was still getting erratic readings. I put both of my multimeter leads on the the head and kicked it over and the spikes were showing on the meter every time I kicked it over. The only thing that was left was the ignition circuit grounding somewhere.