Loss of power (electrical)

jvdavidson

jvdavidson

'78 XS400-2E
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Have a 78 XS400 and I need to figure out why this thing keeps cutting out and dying on me, usually at idle waiting for traffic lights - at those points, it doesn't seem to be electrical, the idle rpms just intermittently 'blip' and drop, sometimes it recovers, sometimes it dies and when it dies in the middle of an intersection when I'm waiting to make a left turn I get pissed - I live in the city of Chicago and commute to Loyola University with my bike - having your wheels all of a sudden die in the middle of a Chicago intersection is NOT GOOD. Today it died twice, differently though - like complete loss of electrical power to everything while I was moving around 15mph approaching a red light, it was during the day so I couldn't tell if the headlight went out but the turn sig indicator was out and neutral indicator went out too, when I completely stopped, the lights came back and it fired right up with one kick - this scenario happened twice today within 5min.

Battery cables are tight as of two days ago. Timing is right as of about 3wks ago, valves were adjusted minutes before adjusting the timing, spark plugs and wires are all new (3wks) carbs are clean and balanced (I will confess that they were balanced PRIOR to the rebuild during an attempt to smooth a rough idle right after I bought the bike and I haven't gotten around to double checking the balance since rebuild - this was 3wks ago). Battery could very well be old and on its way out, not sure but I'll get a new one this weekend.

Not familiar with automotive electrical systems. I theorize that the entire system is self-sustaining once the motor and thus alternator is running and battery is only needed to power ignition when starting it. If this hypothesis is correct then I should be able to start it with the battery, then disconnect the battery and observe the bike continue to run fine - I have not tested this hypothesis yet - I'm an Analytical Chemistry Ph.D. student so I have my hands full until the weekend. If I'm wrong, then I'd imagine that replacing the battery should solve some problems. This weekend, I'll re-check the ignition timing and replace the battery. Any advice would be greatly appreciated!

James
 
Nope. Bike runs off the battery and is a requirement. If your bike is kick start then you can replace the battery with a capacitor. Point is, it is NOT self-sustaining. I don't think a bad battery would cause complete power loss. Has the wiring been touched by outside hands? You need to check all your connections and make sure they are working. Bullet connections are not recommended site wide. if you use them, you should dab some solder on them. If you are still using bus fuses, you should replace them with blade fuses. That is the most likely problem. Could be the kill switch if your indicator lights are still on.

If it is complete power loss, the ignition or the wiring in/out of ignition could be bad. Bad connections have a habit of only being bad when your riding and are then perfectly fine while your looking for them. It can be very tedious and annoying.

Look here and find your diagram http://www.xs400.com/forum/showthread.php?t=4466 See if you can find out anything from that and good luck.
 
Oh and balance your carbs after every alteration you make. That includes adjusting timing, valves, carbs, exhaust, air intake, or anything else that has to do with the engine.
 
Engine dying in the middle of busy intersection is no fun... been there, done that...

Check the battery first. If it is weak - turn signal or stop light can kill the engine at idle.
 
My guess is the carbs are still dirty or out of adjustment. If the bikes is loosing electrical power than that is another issue.
 
Update - like all electrical issues, it came and went ... and came right back again. On my way to and from school on Friday, she ran like a champ, never died. On my way out to visit my parents in Chicago suburbs, it ran perfectly all the way down the interstate until I went to exit the interstate. I hit my turnsignal to exit and immediately lost all electrical power, ignition, headlight, spedo and tach lights, everything. I turned the turnsignal switch off and everything fired back up (obviously since I was rolling about 45mph the bike basically did a push-start). As a scientist I conducted an experiment to confirm what I had observed and again, turning the signal switch caused absolute electrical loss. I tested once again and the same observation was made. My second test sought to determine if something was wrong with the turnsignal switch or if the problem lie elsewhere. To do this, I turned off my headlight THEN hit my turnsignal and indeed, the turnsignal activated and no power loss occurred. My preliminary conclusion was that the alternator (or stator) cannot handle the current draw of the turnsignal module + headlights + tail-light + instrument lights + ignition. Further down the road 5min later I tested the turnsignal deal again but there was no loss of power. This turnsignal issue does make some sense, I've indicated that I've died out in the middle of an intersection numerous times ... well, in each of those situations, the signal was on along with everything else - sort of like an intermittent blip whereby the alternator - or stator, don't know what the difference is - loses its ability to put out sufficient power for everything running at once. I appreciate the advice thus far and am now positive that this issue has nothing to do with my carbs - which makes sense as it purrs like a kitten 99.9% of the time. Any further advice would be greatly appreciated.

Regards,

James
 
Update - like all electrical issues, it came and went ... and came right back again. On my way to and from school on Friday, she ran like a champ, never died. On my way out to visit my parents in Chicago suburbs, it ran perfectly all the way down the interstate until I went to exit the interstate. I hit my turnsignal to exit and immediately lost all electrical power, ignition, headlight, spedo and tach lights, everything. I turned the turnsignal switch off and everything fired back up (obviously since I was rolling about 45mph the bike basically did a push-start). As a scientist I conducted an experiment to confirm what I had observed and again, turning the signal switch caused absolute electrical loss. I tested once again and the same observation was made. My second test sought to determine if something was wrong with the turnsignal switch or if the problem lie elsewhere. To do this, I turned off my headlight THEN hit my turnsignal and indeed, the turnsignal activated and no power loss occurred. My preliminary conclusion was that the alternator (or stator) cannot handle the current draw of the turnsignal module + headlights + tail-light + instrument lights + ignition. Further down the road 5min later I tested the turnsignal deal again but there was no loss of power. This turnsignal issue does make some sense, I've indicated that I've died out in the middle of an intersection numerous times ... well, in each of those situations, the signal was on along with everything else - sort of like an intermittent blip whereby the alternator - or stator, don't know what the difference is - loses its ability to put out sufficient power for everything running at once. I appreciate the advice thus far and am now positive that this issue has nothing to do with my carbs - which makes sense as it purrs like a kitten 99.9% of the time. Any further advice would be greatly appreciated.

Will buy new battery tomorrow - no clue how old this one is - and spend some time looking into wiring. To answer a previous question, the previous owner basically rewired some business under the tank therefore I'm not sure whether or not there was a fuse block in the original bike but I can say that Joe Q. Oldowner rigged up fuse-holders with blade-type fuses along numerous wires near the battery. I have a personal preference to solder everything so that once I get into rewiring this thing myself, I can be assured that my connections are solid.

Thanks again for your feedback,

James
 
Last edited:
Test the volts at the battery when the bike is at 5k rpm's. Should be around 14.5 if it is much lower the charging system has an issue. If that tests ok I would look for a short or grounding issue in the wiring.
 
Ok so first of all, thank you again for your advice thus far, today I've done further digging into the electrical charging system and have found the following: 1) I checked the voltage with the bike revved up to 5000RPM and found only about 13.3V so it's obviously low. 2) I visually inspected the alternator/coil system and all looked fine. 3) I referenced the manual I have for testing the coil resistance and that of the alternator and everything is handsomely in spec. 4) I then moved on to the rectifier and where I was supposed to get some reading in one direction, then reverse the polarity of my Ohm-meter and get no reading (one-way diode obviously) - well, I didn't get any reading in any direction so I'm a little confused there as I'm quite certain that if a diode blows out, you'll get no or minimal resistance in either direction - my meter didn't read anything, not zero or anything, it acted like I wasn't touching anything - I'll take one more look into this. 5) I let the rectifier go and moved onto the voltage regulator which is where I'm stumped. I've been working on cars for 15 years and motorcycles for 9 years and have never encountered a more useless manual than what I have for this bike ... call me a child but I like having lots of pictures diagraming what the manual is talking about and this thing is dry. It mentions a screw which bears against a spring steel plate which allows some adjustment to the output voltage and describe how to adjust it with the bike running ... I'd love to see a picture of that screw as I do NOT see a screw against spring steel on this thing. I see a piece of spring steel but there's not screw on it.
 
Maybe that is part of the problem, ( the screw missing). You can replace the regulator with a new solid state one or just replace all of it with a rec/reg combo unit. There has been a few that has done this already.
 
Does the unit look like this? There should be a way to adjust it under the cap. I don't have one to look but from what I have read it a simple process:shrug:
 

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