Weird Electrical Bug

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ubp2010

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Hello all,
I have been lurking for a while and have learned a ton from this site. I have a 1980 XS650 with TCI. It was running perfect up until a few weeks ago. Every electrical test I could find in the manuals or on here has been within specs. The brushes are fairly new and barely worn.

When everything is hooked up, it charges but runs like total bunk. It has a lot of trouble making it to 2500 rpm. When I unplug one set of the stator to regulator white wires it will run like a champ. It also runs great on just the battery, with the charging system disconnected.

I have a spare TCI, rotor, stator, reg/rec, ignition, kill switch, and I have tried them all and they have done nothing.

Any hints? Suggestions? Questions? I am at a loss.

Thank you for your help
 
ubp2010,

Well, I have had a few vanity plates on my vehicles over the many years, but people could always figure out what they meant. I'm stumped by "upb2010".....

You either have a weak trigger magnet on the rotor or your TCI black box is on its way out. Try epoxying a magnet from Radio Shack on top of the trigger magnet on the rotor and see if that helps. Make sure that you match the polarity of the trigger magnet.
 
I have one on there. I will double check the polarity. The weird thing is that it runs perfect when it's just off the battery. Spare TCI runs exactly the same, poor with the charging circuit hooked up and fantastic with it disconnected.

ubp stands for Ugly Bass Player, from my musician days
 
To me it sounds like when the engine is running the exciter circuit for the alternator is drawing way more power than it should. Disconnecting the rectifier takes the alernator out of the circuit, thus removing that load. Swapping all those charging system and ignition parts and having the problem not change is a pretty good indicator that they are good. That leaves the wiring harness.

I'd venture to guess one or more of the white wires from the regulator to the alternator are shorted either to each other or to another wire somewhere in the harness or (less likely) to the frame of the bike. I'd unplug the rectifier and the alternator plug at the motor, then check the white wires for continuity with each other, the other wires in the harness and the frame. For instance, with the harness unplugged there should be no continuity between the white wires and, say, the red/white wire. If there is continuity, go down the harness till you find where it's shorted.

I have also seen weird shorts where two wires, both carrying power, were pinched together causing all sorts of weirdness like stuff that couldn't be turned off, etc yet since they were not shorted to ground no fuse would blow.

I think on the later bikes the safety relay is also involved via the yellow wire which should have a diode in it. You might check that as well.
 
With Everything off, the battery reads 12v. With it running like crap and the alternator hooked up it slowly climbs to 13.4v at 2000rpm (choked idle.) It is sputtering and missing.

We are tearing into the harness now looking for any shorts with the meter. I will look at the safety relay too.

Any other suggestions are appreciated. Thank you all!
 
I checked all the wires last night with a meter and everything rang fine. Inspected the wires in the harness and everything looks good. I will try the spare coil tonight just to try it. It rung out fine on Primary and secondary tests.
 
I have a bike that is giving me symptoms similar at times. It appears that the charging system is overcharging. Ging easy keeps the vo;tage where the ignition ikes it and it runs fine. When it runs a while and i get on it it runs real bad. Found that the voltage continues to rise. I got readings over 15V with a high rev in the garage. I figure it got higher when blasting down the road. My set up uses points so I figure the capacitor and coils aren't liking that much juice. I swapped out anther regulator and the same. Must be in my stater mod going to the ungrounded brush holders and rewiring the connector plugs.

Try to read voltages at 4500+ rpm and see if it is high.
 
13.4 is about the right charging voltage. Hmmm. With no shorts, I'd be tempted to say TCI but two different ones do the same thing... you might want to pop the cover off and look at the Zener diode, see if it's bubbled. Zeners are generally used as voltage regulators. This is from my TCI box:

100_0784.jpg


It's the orange diode, next to the two large resistors and almost directly above the second white wire. If you look carefully, you can see that one side is gray and bubbled looking. The bike ran OK with this one, but if yours is bad enough... still weird that two TCI's do the same thing.

You might also try jumpering the two kill switch wires, i.e. bypass the kill switch. Corrosion in those terminals could do strange things.
 
That's true. Definitely worth checking. ABS controllers will go nuts if metal fuzz sticks to the sensors, wonder if these TCI's will too?
 
The bike sputters and misses so bad I can hardly get it to idle so a reading at 4500+ rpm is not possible now. I will look at the Zener diode this weekend and see what it looks like. I will also clean the connections and the pickup to see if that is playing into it.

I replaced the egg diodes shown in your picture with 1N4005's and that did nothing. While I was in there I also fixed a few of the bad solder joints. I bought the transistor at the same time but did not replace it yet. Could that be doing it?

Thank you folks, it is deeply appreciated...
 
I replaced my Easter eggs and transistor too, just because. All my troubles turned out to be in the carburetor idle circuits, a set of VM's fixed it right up. But my bike ran like crap no matter what.

Here's an idiotic stupid question: how good are the plugs? I had a set of Iridiums which fouled and it ran like dogshit. Maybe a quickie check would be a clean fresh gapped set of plugs...
 
Don't forget simple things like plugs and coil. I had a coil crap out recently though it measured good. It was a high voltage only short in the secondary. Measured fine with a meter using of course low voltage.

If two tci's do the same thing it's pretty confident it's not the tci.

We're assuming I think that you measured the pickup.

The polarity of the magnet, it would only stick on the right way. It would repel pretty hard the wrong way.

There are uber meister high strength magnets you can buy that are used for things like picking locks, moving the internals of locks around. I once tried to set one down on a filing cabinet and it jumped out of my hand and broke in two. Luckiky it didn't break my finger. One of those sticking to the rotor magnets for a few minutes and I bet it would recharge a rotor magnet. Especially if you tapped the area some with a hammer while it was there.
 
Another thought: be certain the TCI is well grounded. If the ground point to the frame in the wiring harness is corroded, loose, etc that can lead to some goofy stuff. This is the kind of thing that a voltmeter won't test real well. You might try setting the voltmeter to ohms, disconnect the battery positive cable, then do a resistance check from the TCI ground wire in the harness plug to the negative battery terminal and see what you get. A few ohms is not a big deal, the resistance of 18 gauge wire is roughly 6 ohms per 1000 feet. http://www.stealth316.com/2-wire-resistance.htm

The connectors and also your DVOM contact areas will add a few ohms, maybe another 10 or so, so if you get 20 ohms that's probably not too bad. Now if you get, say, 100 ohms then I'd check the ground point (and all other ground connections) very carefully.
 
Sorry it has taken a while to get back to you all, I've been really busy. We stripped the entire wiring harness to look for any shorts or severe kinks or anything funky. There were a few ground wires that were missing some insulation. We fixed those and it changed nothing. The ground circuit is functioning great. We installed a brand new reg/rec and that did nothing.

It still runs like crap with the charging circuit hooked up. Every component of that circuit has been swapped, as well as plugs and coils. We have fantastic spark, it just skips and pops with the charging circuit connected. Running of the battery it is a beast.

I have a different style of TCI that does not appear to have Zener. The perplexing thing is that it runs awesome off of just the battery.:banghead:

Any other ideas? Thank you all so much
 
Had a really stupid thought: could the TCI pickups be somehow getting a signal from the charging system brushes? Maybe the wires are rubbed together and touching inside the left case harness somehow?
 

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