1981 XS 650 Special Wont Rev Over 2500 RPM

XSCody

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OK, so here's the deal. I bought an 81 XS650 Special a few months back that had typical charging system issues. Come to find out the rotor had a short circuit in it and was only reading about .2 ohms. So naturally I replace the rotor. And the problem was fixed, My battery was seeing around 14 volts at 3500 - 4000 rpm. So I'm out for a ride after its fixed and it is running like a top, then I fill it up with fuel and shortly after that It will not rev above 2500 rpm in first gear, shortly after that it will not rev over 2500 in second gear, but once you're up to speed the bike runs great with no hesitation. So then I figure hey I just pressure washed this bike maybe there's some water in the fuel system someplace. So I drained the float bowls and found no water, I then added some sea foam to the fuel thinking maybe I could save tearing into the carbs to fix a small fuel system problem. After that the bike would not rev over 2500 RPM period. So I pull off the left cover and remove one of the brushes for the rotor and the bike runs perfectly! I am a little confused about what is going on here. Maybe when the rotor is magnetized the pickup magnet for the TCI isn't strong enough? I've read some things about putting an earth magnet on the rotor? Are the aftermarket rotors just sub par? I'm new to bikes but have mechanical knowledge. Any help on my issue would be greatly appreciated.
 

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Some of the replacement rotors sold were notorious for this.
The rare earth magnet is the cure.
Did you happen to measure the thickness of the replacement vs. the original?
It has been several years but it seems I remember they were thinner placing the magnet further away from the pickup?
 
Good to know, Where do you attach the magnet to? Is there any place that has a good picture of it? I did not even think to measure the thickness. Its just weird to me how it ran fine at first but after about 10 miles it started to act up.

Thanks for the input!
 
You would epoxy the new magnet over the old. Just make sure the magnets are pulling to each other instead of pushing away if that makes sense.
WARNING I get confused about a lot of things or don't convey what I'm trying to say well in written form so you might wait for advice from one of the guru's. You would be in better hands.
I just thought I'd answer cause you're new to the site. Glad you found us. Welcome.
 
Thanks a lot! Looks like I'll give the magnet a try, I just need to find a place that sells them because all the radio shacks in my area have gone out of business. I really appreciate the quick response and all of the other great info on this forum! So thank you!
 
One test you can try is to unplug the connnector for the reg/rec. This disables the charging system by stopping the current flow through the rotor. This stops the magnertic feild. If the bike runs well that way then you need the new magnet. If it still won't run right it could be the TCI box.
Might want to do a search on TCI, ignitor box repairs. Or some form of those words.
Leo
 
Thanks y'all, I was able to find a high temp earth magnet online. It should be here by the end of this week. Going to epoxy it on and hope for the best. Again, thank you all for the input on this one! It was a real head scratcher for a while but it sure seems to make sense to me now.
 
Update, JB'd magnet to rotor and shimmed pickup with small washers, works flawless! Thanks for all the help!
 
Thanks y'all, I was able to find a high temp earth magnet online. It should be here by the end of this week. Going to epoxy it on and hope for the best. Again, thank you all for the input on this one! It was a real head scratcher for a while but it sure seems to make sense to me now.

I'm having the same problem with my 83 xs650. Revvs up fine with the regulator unplugged. Where did you find hest resistant earth magnets? Hoping that will solve my problem too
 
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