TCI Box Issue?

shortTRIP

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Hey guys,

I need a little bit of help. I don’t know much about electricity and it’s mysterious ways, but I’ve been having an issue with my ‘81, and I’m pretty sure it’s electrical.

I found some older threads where a couple of members experienced the exact same symptoms on their TCI XSs, and apparently solved their problem with a new TCI/CDI box. The only difference is that with mine, the issue seems to come and go. It will either run fine, or well.... it won’t.

http://www.xs650.com/threads/idles-fine-but.9603/

http://www.xs650.com/threads/idles-fine-but-pops-back-above-that.7316/

Mine is doing the exact same thing. It starts and idles perfectly, but as soon as I give it throttle...pop, pop, pop, pop. Everything just fires really slow. Both cylinders are firing. I’ve checked the compression, it’s good. The spark is good during idle, the carbs have been 100% cleaned, rebuilt, and synced diaphragms and floats are good. I checked for vacuum leaks, I checked the coil (even tested a different, functioning one). The rotor is definitely on its way out, but still charging fine. The brushes are a bit worn, but still making contact (I ordered a pair to be safe).

After everything, it has made ZERO difference. I even re-jetted the carbs and played with the (new) mixture screws a bunch. So before I go and spend 150 dollars on a CDI/TCI box that may not solve the problem, I wanted to see if anyone else has experienced this issue.

I’m kinda lost at the moment fellas. Any input or advice would be greatly appreciated.

Thanks
 
shortTRIP, try this simple test.

Clean the plugs.
Regap them smaller, like 0.015"-0.020".
Reinstall, fire it up.
Make note of any changes...
 
Hey 2M, I gave it a try. I set them both to about 0.018”... it fired right up and ran perfectly. However, the issue comes and goes each time I start it, so it’s still difficult to tell if it made a difference. I’ll ride it a bit more and see if it persists. Why would the gapping make such a an impact?
 
... Why would the gapping make such a an impact?

In your first post: "as soon as I give it throttle...pop, pop, pop, pop."

One thing that occurs when the throttle is opened, is the manifold vacuum drops (gets higher pressure), and this greater induction increases the compression pressures, requiring higher spark voltage to jump the gap, putting more strain on the ignition system. Reducing the gap reduces this strain, easier to spark.

If it doesn't change the symptoms, then you can look deeper into fuel issues.
If it *does* change, then you can suspect something in the ignition.

Just a simple test to help figure which fork in the road to take...
 
However, the issue comes and goes each time I start it, so it’s still difficult to tell if it made a difference.
Did the problem change? That's what 2Ms getting at. If it always popped before you closed the gaps and now it comes and goes... that's a change in symptom. If that is a change in symptom, then follow that lead... maybe close the gap to .010" - .015" and see if it becomes less "iffy."
 
Thanks 2M... that makes sense.

Jim, I meant that the issue is always come and go, which makes it difficult to determine whether or not closing the gap actually made any change. I have to run it a few more times to see for sure if this made a difference. If so, I’ll close them up a bit more and go from there.

If a “hard” spark IS an issue, can I assume the TCI may be the culprit?
 
....If a “hard” spark IS an issue, can I assume the TCI may be the culprit?
Could be... more likely though is the coil. I know you said yours ohm'd good, but you can still get a breakdown (under load) in the secondary windings that wouldn't show up with an ohmmeter.
 
Hmmmm... you may be right Jim. I’ve tried a different coil, but that one was used too. It’s not unlikely that one was shot also. Do you know of a sure fire way to test that?
I’ve ran the bike 3 times in a row now with no issues, after closing up the gap.
So It’s gotta be ignition!
 
No worries. I’ll try some stuff.
Careful about throwing just any coil in there. Those TCI boxes can be some sensitive little buggers. They want to see about two and a half ohms on the primary. If you hurt it's feeling, it might let out some smoke in protest... :)
 
Just for everyone's information that might not know there is a guy on this site that repairs these boxes and has built a test stand to test them.

Try sending a private message or I guess the new term is "Start a Conversation" with "rickthefix".

If no response I do have his email address.

Ken
 
Careful about throwing just any coil in there. Those TCI boxes can be some sensitive little buggers. They want to see about two and a half ohms on the primary. If you hurt it's feeling, it might let out some smoke in protest... :)

Haha! Thanks for the heads up, I’ll keep that in mind!

Just for everyone's information that might not know there is a guy on this site that repairs these boxes and has built a test stand to test them.

Good to know Ken. Beats buying a new one. I’ll see if I can contact him here.
Thanks
 
Make sure you have full battery voltage on both sides of the kill switch when it's closed so you have full voltage at the coil. What kind of coil are you using? I had two expensive Chinese ones go bad quickly, and the ignition wires slowly creeping out of another one gave me an extra gap, till I got a meter on it.

Another test you can do is see if it shows the symptoms with the generator disconnected. Supposedly fields from it can interfere with a weak rotor magnet
 
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What kind of coil are you using?

It’s actually the original coil. I’ve never needed to change it out until now. The other one I tried is the exact one from another ‘81. It changed nothing.

Another test you can do is see if it shows the symptoms with the generator disconnected. Supposedly fields from it can interfere with a weak rotor magnet

That’d be a first for me :umm: but I’ll give it a shot. I suppose now is the time to try it all, with everything exposed.
 
Haha! Thanks for the heads up, I’ll keep that in mind!



Good to know Ken. Beats buying a new one. I’ll see if I can contact him here.
Thanks
Short trip, If no reply "start a conversation" with me and I'll give you his email address.

Ken
 
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