Starting issue/Low Volts to Coils

BossAuss

81 XS BRat
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I have a 81 xs400 i bought awhile back and got it running. While out of town i told my brother he could ride it. He couldnt get it started and after checking for spark he got nothing. I checked power to coils and im only getting 1-2 volts. Battery reads 12v, headlight and taillight read 12v but voltage drops to the coils...Any idea what could cause this random loss of power? i really dont want to tear apart the harness until I know thats what needs to be done
 
When checking power to the coils, as I understand it they receive pulsed power from the ignition box. Is that correct? My tester was jumping between 2-5 volts, HOWEVER I assumed that was because the pulses were so fast, and the tester I have doesn't refresh feast enough.

I realize this is an old post, but I am curious if anyone has a solution to this. I am having a somewhat similar issue. Mine was working fine, and started one night randomly when I was parked at a store.
 
You've asked for a solution but didn't actually state what the symptoms are.

The ignition coils get battery voltage at all times. The ignition box or contact breakers both control when the coils go to ground.

You should get battery voltage on the Red/White wires on both coils.
 
haha, now that I reread my post I can see that... Sorry about that! Basically, I have no spark on either side. It stopped VERY randomly. I rode it to the store, came back and havent gotten it to start since. Had to tow it home.

so I should be getting constant 12v on Red to ground, and also constant 12v on White to ground? What should change when I hit the starter button?
 
seems to me, there is a very detailed explaination in the manual. Breaks it down 2 or three different ways.
I don't have time to look it up now, perhaps when I get home.
Tobie
 
Could you point me in the right direction to find that information in the manual? I was home this weekend, and checked it out - it has 10v to the red wire, and 4 on the orange wire. Similar on the other side - 10v on the Red, 4 on the gray. Is that right? My battery is good, Im jumping it from my car. I confirmed a full 12v where the jumper cables clip onto the wires, so i know the battery/connection is good.

@arfstrom - I see youre from Hudson, I go to University of Wisconsin Stout and live in the Twin Cities, I drive through there all the time! Funny to see someone live so close!!
 
All depending on what uniform I am wearing, depends on if I go the north of the runway or to MSP airport. (Air force vs TSA)
Do you have a warm place to work on your bike? perhaps, I can drop by.

Common warning, don't run the vehicle engine that your jumping the bike with.

Okay, from the Tech Tab, one of the links was XS400 Manuals. first post in there is the 360-400 service manual, Page 25 of 34 has some checks to check.

from top of the garage, is a 45 meg for all 400's. Page 19 of 266 has specs for the coil. page 104 of that same book, has a break down of the test. now note: Bold this -- what bike is this segment talking about? validate that this is for your bike. ((Disclaimer))

mostly from bike to bike, the stuff is the same, but some things are not. always make sure that everything is right. weird my name is a original poster. Well I wasn't I just got tired of people finding the original post, and msg the author, and not read the 23rd post where he found a spot he can upload a 45 meg file. Totally worth while to have that post "Stickyed" and everyone can download it for free. There has been countless post on everything. Most of the time there is nothing wrong out side a few common fail things, (coil isn't one of them, getting them backwards is a common problem) I took mine to a yamaha dealer, and they tested them, said the spark was so strong, that they remembered it the next time I stopped in, 2 years later, and at a different site.
 
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I do have a warm place, located in Minnetonka. That would be awesome if you did sometime! I can PM you.

I had looked over that manual in the past, but it was a little more detailed than the DOHC version. I tested my coils, and they test within spec. So we can rule the coils out I think. Since I am only getting 10v at the coil (red wire) is that why it wont charge up enough to fire and create a spark? Does it need to have 12v to fully develop the proper dwell on the coil? I was reading about 17K on the secondary side of the coils with plugs, and 9K without (which is within spec). What resistance rating should my spark plug caps be at? I mean, these are the same caps I had been using all summer and the bike had been working fine.
 
Your above my comfort level, still would mind to stop by. The thoughts I have is, 1 a drop in voltage is possible on the SOHC on the wire to the stop switch or key.
Then the next potential drop is shot wires. which on the sohc is the white wires from the stator to to the first connector. when you move them, they crackle. meaning that any flexibility/continuity/ what ever it takes to fry wires, and turn them into toast. is possible. e.g. many posts on the replacing the stator wires using the Drewpy's re-wire in the tech section. any other wire retains its flexibility, but this one, just goes crackle, and snap and pop.
Give it a shot.

"Your above my comfort level," I am a SOHC person.
"still would mind to stop by." meant to say I wouldn't mind stopping by.
 
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