1981 XS650 misfiring VIDEO

Galadrium

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Hello,

I have a problem with my 81 XS650. It is misfiring at around 2K rpms and no matter how much throttle you give it is can't get much higher than 2500 rpms. Sounds almost like a rev limiter. However, the bike appears to idle normally.

Here are all the things I've done so far:
Used the Clymer manual and a multimeter to check the ignition coil resistance on the primary and secondary coils and it was within the proper specs.

Replaced the ignitor box with a used box, no change.

Replaced the spark plugs, no change.

Cleaned the carbs - twice, no change.

New air filters, no change.

Here is a video of my problem.

I am really at a loss for what this can be. The ignition system is pretty simple and I think I have tested pretty much everything it can be. Does anyone have any ideas about what this could be? Any help is much appreciated. Thank you in advance.
 
The only test I was a little unsure of was the secondary winding resistance test. I tested the resistance without the spark plug caps on, and got 12K ohms. With the caps it was around 28K ohms. The Clymer manual wasn't specific for exactly how this test should go. It was within spec without the spark plug caps on.
 
I hear what sounds like a banging when it revs, not so much a misfire. First thing I would do would be run it on each cylinder alone and listen. If you're sure it's a misfire then use a light to check what happens to the timing when you rev it. The timing might be doing something crazy. Also check the pickup, since switching ignitors didn't do anything. Should be ~700 ohms from each color wire to the black wire.

P.S. I wouldn't worry about the coil - it's idling fine, so your coil is working.


Also - what's the last thing you did to it before it got like this?
 
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Xjwmx, thanks for the response. Glad to hear my coil is probably ok.

The last thing I did was replace the alternator rotor. It charges fine. It ran well for about 20 minutes then started intermittently having this problem. The problem worsened, to the point that I barely got the bike home.

I measured 765 ohms on each pickup wire to the black.
 
Where did the rotor come from? Some of the replacements sit too far away from the pickup. The magnet for the pickup is embedded in the rotor. It's best to have the old rotor rewound.

Also, make sure the rotor isn't slapping something, because like I said to me it sounds like banging. Listen with your ear down there when you rev it.
 
The rotor came from Ebay, since MikesXS was out of them. I seem to remember this problem happening once or twice before I changed the rotor. Upshifting would fix it and it would run normally.

I'm going to check the rotor and report back. Thanks again!
 
Your caps at 8K ohms each are a little high, should be 5K ohms.

When the rpm will not go above 2500 rpm, may mean the timing is stuck at full retarded. With no advance the engine cannot increase rpm.

Since you changed the rotor, the new rotor may have a bad (weak) pickup magnet. If you still have the old failed rotor, it could be a good test to re-install the old failed rotor and see if the rpm will increase to full rpm.

There are threads on the site where a new magnet (radio shack) was installed on top of the old pickup magnet.
 
Try like xj stated. It almost sounds like the coil is shorting inside itself. And with the resistance you posted, it would not surprise me.Those are way too high. And the coil's were marginal at best when new. The coil and wire set-upm using on my '80 are the 17-6803 coil, the 23-2906 wires, and the 23-3113 plug cap's. This coil is pretty good, has more output than the stock one, and is more forgiving if you happen to lose the ground on the spark plug while checking compression or whatever. I bought all those parts 4 years ago with no problem's at all.
If the engine run's better with one cylinder, try swapping the plug wire's.You want to see if it follows the wires. As you increase engine speed, coil output is increased also, so a shorted coil would cause what I heard. And you are right, it almost does sound like a rev limiter. Of course, the ignition system does not have one.
BTW, ther is a guy who does rebuild the rotor's for reasonable money. The address is in the classified's, I think.
 
I ran the bike on one cylinder and the only thing that changed was that the effect happened at a lower RPM.

I think I will swap the old rotor into the bike just to eliminate the possibility that the pickup magnet is faulty. Although it would be strange that it would run fine and then start having a problem after about 20 minutes. I would think that if the pickup magnet was bad it would have a problem as soon as it ran.

I will check this and report back. Thank you all for your responses.
 
^yes,that would be strange. But the problem is something right in there I think. You should get hold of a timing light and see if the timing advances when you rev it. You can borrow them from a parts store if you don't own one.

Before you haul the rotor back out check the connector at the pickup and harness. I had a problem where the crimp from the wire onto the connector was bad. The connector itself was fine. It was in a different circuit but same kind of connection. You could set the idle up with the screw so that it messes up, and then start flexing the wires at both sides of the pickup connector to see if it causes a change.
 
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Xj, I like the idea about moving the connector while it is messing up to see if it's a bad connection. I'll give that a try.

I'll track down a timing light and see if I can check for the timing to advance. I've never used a timing light before but I should be able to figure it out.

I will try these things and report back. Thanks again for all of your help.
 
I had a similar problem on my 80. Turned out to be the stator shorting for some reason, it in turn screwed up the pickup or something. Charge your battery, unplug the charging system and see if it runs right just off the battery. just pull out the brush/ the one with the power going to it. Think its the brown wire one, and see if it's better. As soon as i pushed my brush back in the bike would fall on its face. Changed the stator and no more problems.
Worked on mine anyway. good luck.
 
Are you sure it's not fuel? Some restriction in the fuel line/petcock etc? On mine I had some high rpm cut out and it turned out to be water in the fuel that had gotten into the float bowls. Drained them and it was fine. Just a thought.
 
^One thing I would like to know, that I can't tell for sure from the video, is after you drop it back down to idle, does it still run or does it die?

If it dies, it's probably not ignition after all
 
This Just happened to me too!!!! I bought a "NEW" Charging rotor off ebay. Drove 20 min too and the SAME thing.. I have tried a lot of the things you did. Whats the fix?

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This Just happened to me too!!!! I bought a "NEW" Charging rotor off ebay. Drove 20 min too and the SAME thing.. I have tried a lot of the things you did. Whats the fix?

Posted via Mobile

not kidding i went through the same thing. If it's a TCI bike seriously try what i said above. As SOON as my bike got HOT (5-10minutes) something expanded in the stator or pickup and did exactly what you're showing. Think i have a vid too somewhere... its easy and worth a shot, i also swapped the reg/rec and the rotor, with no luck. Bikes been perfect for over a year now.
 
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