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puzzling xr650l ignition/timing issue

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Hello all,

Im new to the forum, and thought I would introduce myself with a problem

I have a 1998 XR650L Supermoto that I bought from a friend a couple of years ago and love it. Recently, it caught some kind of bug and is having some interesting running issues.

Backstory:

I went on a ride with a friend, me riding my SV650 and him on the XR. Great ride, no issues. The next day I fired up the XR to run around town to do errands, and noticed that at about half throttle the bike misfires, backfires, and will not increase RPM. I thought it was a carb issue, and having to go out of town, dropped the bike off at the shop to get the carb cleaned, tuned etc. Its odd though, its not that bike bogs or dies, it just refuses to gain RPM. Starts, idles, and runs great in every gear as long as you remain below half throttle.

The mechanic disassembled the carb and found it to be spotless. He put the carb back on, same problem. He happened to have a wrecked but running XR650L in the shop (same year) so he swapped carbs from that bike to mine, Same issue. He then took my carb and put it on the wrecked bike and it revved up fine. So, he swapped the CDI in the same manner which didn't solve the problem and allowed the wrecked bike to run just fine. Same story for the coil, wires, regulator/rectifier, spark plug.

He tested the pulse generator resistance, and it was within spec. I took the bike back and swapped out the pulse generator just in case, and it didnt solve the problem. I bypassed the kickstand/handlebar kill switches and no luck. Cleaned and checked as many grounds as I could find across the bike, and still no luck.

Im perplexed:banghead:, and often came here for answers, so I thought i would quit lurking and join. You all seem smarter than me, so im hoping that someone has some insight on something im missing. Look forward to contributing in the future!

Dave

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forgot to add, it seems to me like the timing wont advance and allow the engine to rev, but i may be mistaken. I think that I have gone through all of the timing related electrical parts, but there may be something that eludes me

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Take the Stator from the wrecked bike and put it in yours..Might be some dud wiring down there causing an intermittent short..,,and of course as above,,Check the valve timing.

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Dunno about that...A half sliced through ignition wire from down there flopping about under movement from the bike (vibration etc) will definitely cause a bike to not run correctly,,It's interfering with the complete system electrically,,had it before on my 86 XR.. It was usually a b,,,h to start and then coughed and farted and carried on with the movement of the wire inside the left hand casing..that's why when I hear Stator problems or electrical problems I always tell people to slice back that outer plastic sheathing over the wires between the Stator and up to where it ends about 6 inches above where it exits the case and give the wires the eyeometer check...An ohm meter will say it's all good when in fact the things holding on by a thread of wire..any movement sets it into interference mode.

and I don't mean slice the plastic from over the wire,,It's that anti burn anti rub type stuff that covers the wires that needs hacking back for the eyeometer check,,

Edited by Horri

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Dunno about that...A half sliced through ignition wire from down there flopping about under movement from the bike (vibration etc) will definitely cause a bike to not run correctly,,It's interfering with the complete system electrically,,had it before on my 86 XR.. It was usually a b,,,h to start and then coughed and farted and carried on with the movement of the wire inside the left hand casing..that's why when I hear Stator problems or electrical problems I always tell people to slice back that outer plastic sheathing over the wires between the Stator and up to where it ends about 6 inches above where it exits the case and give the wires the eyeometer check...An ohm meter will say it's all good when in fact the things holding on by a thread of wire..any movement sets it into interference mode.

and I don't mean slice the plastic from over the wire,,It's that anti burn anti rub type stuff that covers the wires that needs hacking back for the eyeometer check,,

On a bike where the stator powers the CDI directly, yes. But, XRL has an alternator running through the diodes in the regulator charging the battery, and the battery side goes into the CDI as +12V. Problem down there *could* cause problems, just less likely with the +12V system on the XRL.

Dave

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Fair enough,,I don't know enough to pontificate over the fact,,He has access to a spare Stator,,Fit it..Eliminate the Stator as the issue.,,he can check the timing at the same time..

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Check the RFI resistor in the spark plug boot, I have seen them fail and cause the condition you are describing. Replace it with a length of stainless, copper or brass rod and see if that cures the problem.

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On a bike where the stator powers the CDI directly, yes. But, XRL has an alternator running through the diodes in the regulator charging the battery, and the battery side goes into the CDI as +12V. Problem down there *could* cause problems, just less likely with the +12V system on the XRL.

Dave

Got it...Mr Hare sent me a pm clearing up the issue,,Forget the Stator then..No charge in the battery then nothing works..You can keep that system.

Has that CDI arrived yet Brian??,,seems to be taking a long time to get there.

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Hey guys thanks for the ideas! I realized in my frustrations yesterday that I also had a leaky valve cover gasket and the engine/ frame was filthy so I pulled the motor and decided to check the valves, change the gasket, clean the engine and frame, and check the timing.

Turns out, the end of the spring on the cam chain tensioner that rides against the wall of the head had broken off an the tensioner had slackened and cause the chain to skip two teeth on the cam gear. Since I have a spare motor, I pulled the tensioner off the other motor and replaced it along with the cam gear and chain. When I had it all disassembled I turned the motor upside down with a magnet shoved up the timing chain hole an shook the hell out of it. I actually managed to grab the piece of spring affrer about 5 mins of shaking. I re-timed the cam gear with TDC (although it still looks to be a degree or so off) put tho motor back in the frame, added oil and it fired right up. However, I seemed to forget the fact that it was 2 in the morning and due to me not putting the exhaust back before testing (header, no muffler) I got a friendly greeting from a LEO. He was more interested in what I was doing than giving me crap about disturbing the neighbors. I'll put the rest back together today and take it for a test drive to make sure all is well.

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