1980 xs650 cutting out half throttle

[Jake Violando]

So I have a bobbed out 1980 xs650. Well it was running great till my safety relay shit the bed. So I jumped it out. Bike fires and idles fine. But at half throttle it is almost like a rev limiter, just bah bah bah bah. I am getting 12.8 v to the point of the rev limiter feeling. My rotor ohms out to 5.5 ohms. Cleaned my brushes. What am I forgetting?

 

[Jaydela180]

Still running stock tci ignition? Im having same problem with my 80 with stock tci ignition. Opened up box to hopefully find obvious dead/burnt/broken diodes, but all looked good. Battery, rotor and carbs all check good. Got a pamco waiting on bench for install... pretty sure it will solve problem.

 

[Jaydela180]

Let me add...
Tci circuits looked good, but im no professional. Pretty sure something has failed, but figured a pamco is a wise investment.
Your first test should be riding with reg/rect unplugged to see if symptoms disapppear. If they do, the magnet in rotor has lost some magnetism and needs new one glued atop it. Start there and report back

 

[Jake Violando]

Let me add...
Tci circuits looked good, but im no professional. Pretty sure something has failed, but figured a pamco is a wise investment.
Your first test should be riding with reg/rect unplugged to see if symptoms disapppear. If they do, the magnet in rotor has lost some magnetism and needs new one glued atop it. Start there and report back

I did the test with a feeler gauge on the magnet on the stator cover. No magnetism. What size magnet should I glue on top off the old one?

 

[Jaydela180]

Lots have recommended a magnet from radio shack, but it was hard to locate for me because almost all chicagoland stores have closed.
The size youre looking for is 3/16 diameter by about 1/8 thick.
Use jb welb and mind polarities.

 

[Jake Violando]

Should I just buy the PMA kit? The black magnet now has no pull

 

[angus67]

Look at refer magnets at walmart. Ive found a few 3/16x1/8 magnets on some, and they are pretty strong for thier size. I haven't needed to glue one to my rotor yet, but when i need to, refrigerator look out!
At what ohms is your rotor sitting at? Try the slap test again with the ignition on. But i dont think thats the problem.

 

[Jaydela180]

You buy the pma... you also need new ignition. Pma rotors do not work with tci ignitions.
I would spend 5 bucks first for a magnet.

 

[Jake Violando]

I have a strong magnet like that size actually. Maybe a tad bigger. But with the slap test, I have nothing. With the rotor sitting I have 5 ohms. Brushes are good just inspected them. Can't figure out how tbeh go in. I'm so flustered right now. Been working on it all day because I had to trace and jump out a short, my safety relays. SOO do I just glue a magnet to my magnet on stator cover? And try it? When you fire the bike up it idles great and fires first kick. Up at maybe half throttle it breaks up almost like a rev limiter.

 

[peanut]

I'm not convinced the problem is your rotor losing all magnetism overnight at exactly the same time that you remove and bypass a faulty safety relay.....The Rotor was clearly working perfectly before the safety relay gave out

I'd go back to what started all this off ...the safety relay. Check that you haven't disconnected or shorted or disturbed any other wires or connections when working on the relay. Make sure your bypass wire has a good connection . This issue could simply be down to a high resistance, bad connection breaking down under load.

 

[Jake Violando]

I'm not convinced the problem is your rotor losing all magnetism overnight at exactly the same time that you remove and bypass a faulty safety relay.....The Rotor was clearly working perfectly before the safety relay gave out

I'd go back to what started all this off ...the safety relay. Check that you haven't disconnected or shorted or disturbed any other wires or connections when working on the relay. Make sure your bypass wire has a good connection . This issue could simply be down to a high resistance, bad connection breaking down under load.

Sorry I should've gave more information. Sometimes the bike would do this exact thing I described until it was running for 10 minutes or so. I figured it was the bike warming up. Now it's worse.

 

[gggGary]

I'll differ a bit from Peanut. Long distance, I think the safety relay is acting EXACTLY as expected. By design If charging quits the headlight does NOT come on. A TCI bike not liking to rev, is a further symptom of a charging system that has died. I have been finding dead regulator/rectifiers fairly often now. short the "regulated ground" brush to ground, check that you have +12 at the top brush, watch the volt meter when you rev it. Thanks to 5T for this excellent pic.

If it charges, you have your answer. Do not run the bike long with the brush shorted, the alternator will overcharge the battery and overheat, cooking the rotor as it goes full power, full time. As always a KNOWN good battery, good fuse box, clean contacts and switches, and no shorts in the wiring.

 

[Jake Violando]

I'll differ a bit from Peanut. Long distance, I think the safety relay is acting EXACTLY as expected. By design If charging quits the headlight does NOT come on. A TCI bike not liking to rev, is a further symptom of a charging system that has died. I have been finding dead regulator/rectifiers fairly often now. short the "regulated ground" brush to ground, check that you have +12 at the top brush, watch the volt meter when you rev it. Thanks to 5T for this excellent pic.

If it charges, you have your answer. Do not run the bike long with the brush shorted, the alternator will overcharge the battery and overheat, cooking the rotor as it goes full power, full time. As always a KNOWN good battery, good fuse box, clean contacts and switches, and no shorts in the wiring.

Great I'll try that soon. Battery is new. Safety relays are jumped correctly and neatly. My rotor ohm'ed to 5.5 ohms yesterday, my test leads did have about .5 ohms to them tho. Would this be a bad rotor? Also tried the slap test and have no magnetism whatsoever. This was intermittent and now it's as soon as you touch half throttle maybe less.

 

[gggGary]

Rotor seems OK..... do the ground test next. New does NOT equal good, ESPECIALLY with batteries. Load test the battery anytime you are having charging system issues. Since you hard wired the headlight, testing is easy, Fully charge the battery, then switch on, kill switch off for 10 to 15 minutes, bike should still crank over and start.

 

[Jake Violando]

Running, I was getting 11.6 v at the spot I should've got 12. And grounding that out didn't change anything. Should I keep inspecting charging system, or re check valves and carbs. I just adjusted my chain and did valves not long ago. Also the carbs were tuned up and put new diaphragms in. Rest of carb parts are old.

 

[gggGary]

IMHO I'd stick with getting to the bottom of the charging system issue for now. Did you check for +12 on the other brush?

 

[peanut]

sorry Jake I completely misread this. I thought that you already had a PMA fitted I'm mixing up 2x threads ....
must pay more attention ...must pay more atten..........

As gggGary says you need to check that you have 12v+ or thereabouts on the outer copper track of the Rotor with a mulitmeter and the ignition turned on. Its damn fiddly working through the stator holes but it can be done. Then as gary says run a bypass wire from the inner ring (black wire on the stator) straight to negative on the battery.
Then with the ignition on do a slap test to check for a magnet field .
If you still don't have an electro magnet at the rotor then you must be missing something in the test process

 

[Jake Violando]

IMHO I'd stick with getting to the bottom of the charging system issue for now. Did you check for +12 on the other brush?

Yes, both brushes have below 12v and even revving it won't jump above 12. Brushes look good and plenty long

 

[Jake Violando]

sorry Jake I completely misread this. I thought that you already had a PMA fitted I'm mixing up 2x threads ....
must pay more attention ...must pay more atten..........

As gggGary says you need to check that you have 12v+ or thereabouts on the outer copper track of the Rotor with a mulitmeter and the ignition turned on. Its damn fiddly working through the stator holes but it can be done. Then as gary says run a bypass wire from the inner ring (black wire on the stator) straight to negative on the battery.
Then with the ignition on do a slap test to check for a magnet field .
If you still don't have an electro magnet at the rotor then you must be missing something in the test process

Sooo my rotor reads no volts with key on and 6ohms resistance. Kinda funky. Just to verify it's his outer ring?

 

[gggGary]

Well for voltage tests I'd be checking at the brush screws with the brushes installed switch on. If you aren't above 12 volts on the hot brush then fuse holders, ignition switch, battery ground strap, etc. etc. could need attention. You are aware of the goofy braided wire wraps around the brush retainer install right? Since anything is possible on these old bikes you are positive you have the correct set of brush holders and reg/rec?