XS650SK runs poorly when warm

[jetmechmarty]

I take my '83 XS650 for a ride and it will run terribly once warm and away from the house.. She'll go 50 mph with the throttle twisted to the stop. If I pull off the road she goes back to a perfect idle. Pull back on the road and she goes back to bucking and snorting. It's a one kick start, even after months of sitting.

I pulled the TCI. I see no cold or broken solder joints. It looks new in there. The magnet on my rotor feels strong. My screwdriver is pulled right to it. The pick-up coil unit showed corrosion on the face. I cleaned that up.

Any ideas? I believe I'm going to send off my TCI. I have no other idea.

 

[Jim]

Any ideas? I believe I'm going to send off my TCI. I have no other idea.

Too bad you don't have a spare one. That's how I figured out mine was bad. Slightly different symptoms, but yeah... started good, nice idle. About 2K it would act just as you describe. If I could nurse it past about 3-3500 revs it smoothed out but as soon as I got below that... poppin' and buckin'. Swapped in my spare and it's been good ever since. 'Course... now I don't have a spare. I'm on the hunt.
And yeah... mine still looks like new on the inside.
Where you gonna send it?
EDIT: Mine only did it when warmed up too.

 

[jetmechmarty]

Where you gonna send it?

I have a friend near Atlanta who fixes them. You kept your broken one? I hope he can fix my XS11 TCI too.

 

[Jim]

I have a friend near Atlanta who fixes them. You kept your broken one?

Yes I did. I'd be extremely interested in working with your friend.

 

[gggGary]

What does your timing light show? put it on both sides. steady signal?
A few of us have found a badly frayed pick up wire where they run near the sprocket, chain.
Weak rotor magnet test, battery charged, disconnect the voltage regulator, take it up and down the road, any better?
Rev it in the dark gas tank raised, any spark leaking out? ohm out coil, plug wires, plug caps, change spark plugs.
Compression test?
Air cleaners open, are both slides opening when you rev it?
Run it up, pull in the clutch and shut it off, what do the plugs say?
Double check vacuum cap on intake, temporarily remove vacuum line to petcock, cap vacuum, port run it on prime position.
run it with gas cap loose.
Have float valve bodies been out of carbs, screens above valves clean, float valve o-rings replaced?

 

[Jim]

What does your timing light show? put it on both sides. steady signal?

Yeah, that's a good test. Timing light on mine went batshit crazy when the revs came up on the bad spot.

 

[xjwmx]

I pulled the TCI. I see no cold or broken solder joints. It looks new in there.

they're practically invisible. you need about a 10x magnifier, and bad ones look like a "slug" attached to the lead has a faint circle around it that separates it from the rest of the solder. you'd think it would make contact, but somehow it's a problem.

before sending it off, i suggest taking a small iron and resoldering every single pad, adding just the smallest amount of solder to each one. it sounds dreadful but it only takes 15 minutes. solder right through the coating on the board. i finally fixed my bad one that way, and did it to my spare as a preventative measure

 

[Jim]

Weak rotor magnet test, battery charged, disconnect the voltage regulator, take it up and down the road, any better?

I'm just gonna throw this out there as a fwiw... seems as good a place as any. During my rotor tooling buildup, one of the tests I did (incidentally) was looking at the TCI magnet. One of the videos I did showed how the copper in the faceplate almost completely blocked the rotors magnetism. allowing the TCI's pickup to "see" the tiny TCI magnet in amongst the rotors strong mag. field. I never mentioned it or videoed it but the magnet is felt on the backside of the faceplate too. What that means is every time the rotor energizes, it refreshes (for lack of a better word) the magnetism in the TCI magnet. So I'd be at a loss to explain how the little magnet weakens.
So why do some guys disconnect the reg/rec (killing the rotor) and find that the TCI works when the rotors not magnetized? Here's my theory... backed up with some anecdotal evidence...
I hope @delagem doesn't mind me tagging him here, but he got a hold of me because his bike was doing the "weak magnet" thing. Worked OK with the reg/rec disconnected, but ran like crap with it hooked up. His bike came to him with an aftermarket rotor... a Chinese one. A light went off and I started searching through some old articles I'd read. There was a member here a while back (name eludes me right now) that had a Chinese rotor ( you were involved in this thread Gary) that didn't run true. He put it on a lathe to true up the faceplate and promptly ate the copper rings. Yep, apparently the copper in the Chinese ones are paper thin. No surprise there is there? So, based on the idea that the paper thin Chinese repops were allowing the rotors magnetism to "bleed through" and confuse the hell out of the TCI pickup, I sent Mike one of my OEM rewinds. It fixed his bike.
So, if your bike acts like Marty's here and disconnecting the reg/rec fixes it, look and see if you're rotor's OEM or a repop. If it's a repop, I'd suggest replacing it with a good OEM 'afore you throw your money at another Chinese copy.
If anyone has experience otherwise, please speak up. It'd be nice to get some more data on this and see if my theory (backed up by one example ) holds up.

 

[xjwmx]

^heat weaken or destroys magnets, so that's a possibility. nobody has ever taken a reasonable gauss meter and compared magnets, to my knowledge. might be a good opportunity if you have a lot of rotors coming through

 

[Jim]

^heat weaken or destroys magnets, so that's a possibility.

Yeah, that's a possibility, but I don't think that's the case. The rotors I'm doing are 40 yrs old and the magnet's are working just fine. So that kinda discounts that idea. My big curiosity is whether or not anyone has experienced the weak magnet scenario on an OEM? Or is it just the Chinese repops that have that problem?

 

[xjwmx]

i worked at a place that had some crazy super magnets around. i was going to stick one to a filing cabinet and about an inch away if flew out of my hand and shattered on the cabinet. they were strong enough to pick locks with, move levers and stuff from the outside. which is why they were there...

anyway, if you could get one of those, lay it against the rotor magnet, and tap the rotor magnet a few times with a hammer, i bet it would charge the rotor magnet back to spec, if not over!

if they originally didn't pay much attention to the strength of the rotor magnets, or material maybe, that could explain some lasting and some not. don't remember anybody mentioning their weak magnet was on an aftermarket

 

[gggGary]

Yeah, that's a possibility, but I don't think that's the case. The rotors I'm doing are 40 yrs old and the magnet's are working just fine. So that kinda discounts that idea. My big curiosity is whether or not anyone has experienced the weak magnet scenario on an OEM? Or is it just the Chinese repops that have that problem?

Can mebbie do some pull tests on the tub of rotors with the electronic fish scale. I think I have seen weak magnets on stock rotors, but not 100% on that.

 

[jetmechmarty]

My rotor has been doing the job since 2002. It’s a rewind I got from a friend on the Micapeak yam650 list. The issue came up suddenly. I plan to send the box off today.

 

[jetmechmarty]

Tested with borrowed TCI. It ran just fine for 25 miles. Hopefully, it will run just fine when my TCI comes back.

 

[Jim]

Ask your buddy if he'll do my TCI box?

 

[jetmechmarty]

Ask your buddy if he'll do my TCI box?

I will!