mystery condition

xjwmx

xjwmx

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Often my bike will stop running for no apparent reason always a few hundred yards after starting off, then thereafter it's fine. I will track that down sooner or later.

The mystery is while I'm going along and it quits, I can pull the clutch and release it and it will start back up, like push starting. Why doesn't it just start itself without needing the clutch pulled and released? The clutch switch is disconnected, so it's not some electrical thing.
 
Yes they are. But the second paragraph is the real mystery.
 
I had a similar situation, but my bike was blowing the main fuse and shutting off. Since I put grommets in the headlight bucket where the harness goes through, I have been able to reproduce that. So, I'm wondering if you have an elusive dead short somewhere.

But you're right... it's a peculiar symptom.
 
its got to be electrical ... I cant think of another reason why the bike would not start until the clutch was dropped again and even then the electrical theory doesn't really hold up because theres no reason for it not to run.
is this a soon to chop bike? stock daily runner? I would say if its soon to chop try making a custom harness and run it so you'll know its not a bad connection, however it doesn't eliminate a lot of the other components
 
Remember it always happens within a few hundred yards of starting up, then it's fine. There's no electrical timer on board....

My best guess at the moment is something to do with the external gas filter. Carbs are clean and petcock is good. Wiring looks good. It started soon after changing the filter to a different kind and mounting it differently.
 
Not vacuum since it still happens set on prime. Was going to eliminate the filter and see what happens when I get a chance. Don't know what it could be with the filter though really. Maybe a bubble forms and blocks fuel lol who knows. I don't....
 
Well if you think the filter is the cause maybe you could use some clear line and see if a pocket is forming. Or could you just run the tank straight into a gas can for a minute or so and make sure the fuel flow stays solid? possible try to rattle the tank a bit
what your saying is making sense ... popping the clutch gives the fuel a chance to catch back up where as not popping the clutch the carbs are still sucking fuel
interesting problem you have
How is your tank mounted, stock bike? rubber mounts right?
 
Try it same as usual but with your fuel tank cap cracked open ie no possibility of tank vacuum forming after start up. Sounds suspiciously like restricted flow and dirty fouled fuel tank cap vent. Bowl runs dry, air gap forms in lines, takes too much time to re-fill lines and bowl after start up. ???

"You pays your money, you takes your choices".....fuel flow restrictions, temporary vacuum locks, vent plugging etc. versus electrical interruptions etc. ??? simple check re cap vent try it.
 
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If it was a blocked vent wouldn't the symptom recreate itself over and over?
Air bubbles in the line won't interfere with fuel flow.
The fact that "runs fine thereafter" would eliminate fuel?
Since the clutch cable flexs when pulled and runs along the wiring harness I would look for places it might "bump" the wiring and the possiblity of corrision in the plug couplings or broken wire.
Let us know how it turns out.
 
It happened last night in a dark area and I realized the headlight goes out when it happens though not the instrument lights. Pop the clutch and she starts back up and the headlight comes back on... I doubt the headlight goes off when you run out of gas, so it's got to be electrical. Unfortunately I'm also having computer probs at the moment and my schematics and so on are on a different semi-crashed comp which I'm going to try to get files off of. I will undo the vacuum and let it run out of gas to make sure the headlight stays on. I expect it to, but it would be possible to design it so it doesn't...

Bluebikerfan, is the vent you speak of the little hole in the center of the cap when you open it? I checked it to make you happy :) Stuck in a dental pick and it went in 1/4" and hit something that felt like it should be there. I had that all apart a couple years ago to put on new gasket so it's probably fairly clean.
 
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If your bike still has the original fuse panel ( 4 glass fuses held by clips), it needs to be replaced with new automotive blade type fuses. Those clip type panels are totally unreliable after many years of use. They can cause intermittant faults such as engine shutting down.

This may not be your specific problem right now, but the fuse panel needs to be replaced anyway.
 
I used to work for this guy and one of his products was a little box he called an event recorder. Great diagnostic tool. Clip wires to everything and wait for a failure. Then upload the box and get a graph of every signal and voltage level vs time. Showed what happened to which signals in what order. Like a high capacity storage scope with a dozen or so probes.
 
"I doubt the headlight goes off when you run out of gas, so it's got to be electrical. "

Isn't there a relay that doesn't activate the headlight until the engine is started ? That would explain why the headlight goes off when the engine dies wouldn't it?:confused:
 
Yes. Possibilities are slowly presenting themselves. But today is fishing day so it'll have to wait :) I suspect a loose connection now. I like remmy1101's theory too.
 
weekendrider said:
Let us know how it turns out.
Click to expand...


It turned out to be the TCI box, which I was abke to repair. See this thread:

http://www.xs650.com/forum/showthread.php?p=34479#post34479

Going through the bike looking for the problem, I found several things that could have caused it but weren't. A tribute to the robustness of the bike I think. Also, it's a tribute to the robustness of the ignitor box that it was working as well as it was.


I can't explain why it took popping the clutch to start it, except maybe it needs a jolt to start. I can't explain why it would always happen only right after starting out, but who knows what was going on in that wacky TCI box. There could be several good theories.

I have a feeling maybe external fuel filters get a bad rap. Something mysterious happens, blame it on a mysterious bubble in the filter...
 
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Very clever to think the diodes went bad. I wonder how many have been trashed because of them? If my 81 starts acting up I will have to check the diodes first thing.
 
xjwmx said:
Remember it always happens within a few hundred yards of starting up, then it's fine. There's no electrical timer on board....
Click to expand...

Hmmm...do you always start from the same place. Maybe you have an old UFO landing strip within a couple hundred yards of your starting point and the residual magnetic and electrical energy is shutting your bike down. :yikes::eek::laugh:
 

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