Lost Spark while riding '78 XS650

[Melnic]

A couple weeks ago, warmed the bike up a few minutes and about 2 miles up the road, lost power. Coasted to a stop.
Bike then started up and I made it home.
Drained fuel into a container and even on ON setting it dumped almost a gallon so I was not at the RES level. Fuel flowed well when sucking on the petcock vacuum line.
I looked at timing and it was retarded some. I had a spare points cam I never put in ad the old one was a bit gouged so I went through the work to install that then reset the points till I was happy. Dwell on the meter was good too around 22/23. It would advance properly.
I then pulled the light and made sure the connectors were clean, then pulled the tank and also cleaned the bullet connectors at the coils. They did not look bad but I cleaned them up some more.
Did a really good warm up today, rode 3 miles @ 25-30 in the neighborhood and it was fine so took onto the main road @40 and did not get 1/8 mile before it cut out.
Started it up and set petcock to PRI in case it was a petcock issue. Ran back 1/8 mile then turned around and headed down and then it cut out again. This time it would not start back up. Pushed it home 3/4 mile to the house. Pulled out timing gun and left side lit on start up some, but right side did not, went back to left side and it stopped lighting. Pulled a new plug and inserted into cap and no spark from left nor right side.

Anyone want to take bets?
Bad ground?
Coils?
Condenser?
Bad 12V feed to coils?

Some things I had done when getting bike running last winter were

• Cleaned up the ignition switch and kill switch contacts
• New Denso brand points
• New Condenser w/ the Denso points
• Valve adjustment
• New Cam chain
• Cam chain tension adjustment

 

[Melnic]

Another clue
Let it sit an hour and now it starts right up.

 

[mike in idaho]

Take a spare spark plug along on your next ride, use it to check for spark, next time it quits.

 

[Raymond]

Melnic, I'm not a betting man, but given the list of runners you've published I would say the lowest odds would be bad ground as the commonest cause of problems, specially intermittent. And from my own hard-earned experience it will be something you've just worked on.

 

[Ratranger]

Could be coils or condensors, I've seen them work fine and fail as they get heat in them, then work again once cooled off. I'd also say do a continuity check of the power wire to coils and points. Wires and connectors can fail from age and movement.

 

[Jan_P]

All symptoms of weak charging or no charging
I would ( being a parrot here again ) measure charging voltage Simple to do across battery .Especially when warm
And check so the fuses are sitting OK

aka --> Bad 12V feed to coils?

But Yes ground has to be checked

 

[Grimly]

Most of the condensers on the market today seem to be of crappy quality.
Not saying that's what the fault is, just bear it in mind.

 

[Melnic]

Most of the condensers on the market today seem to be of crappy quality.
Not saying that's what the fault is, just bear it in mind.

I"ll have to see if I have the original still.
What I used was from a Denso (nippon denso) new old stock tune up kit that the local dealer.

Since the bike goes and all the sudden drops both ignitions, I'm thinking ground or as mentioned the 12V to the coils.
I'll be pulling tank off and cleaning up the ground of the condenser caps to the frame.
I'm thinking I may also pop in a Y tap and run the 12V at the coils back to a 12V LED so if it goes out when the engine goes out I know its the 12V and not the ground.

The last good ride I took before It gave me trouble was a misty wet ride but not that wet.

 

[Its been a long time]

Most of the condensers on the market today seem to be of crappy quality.
Not saying that's what the fault is, just bear it in mind.

Exactly. Recently had one dead on arrival. One set of points dead on arrival too. That was the final straw that convinced me to go electronic ignition.

 

[Its been a long time]

I"ll have to see if I have the original still.
What I used was from a Denso (nippon denso) new old stock tune up kit that the local dealer.

Since the bike goes and all the sudden drops both ignitions, I'm thinking ground or as mentioned the 12V to the coils.
I'll be pulling tank off and cleaning up the ground of the condenser caps to the frame.
I'm thinking I may also pop in a Y tap and run the 12V at the coils back to a 12V LED so if it goes out when the engine goes out I know its the 12V and not the ground.

The last good ride I took before It gave me trouble was a misty wet ride but not that wet.

How old is new old stock? It's possible that the condenser has deteriorated beyond use. They don't last forever. I'm not sure how easy it is to test one in a home workshop.

How good is the battery and charging system? If that isn't 100% that can give you ignition issues.

 

[Melnic]

Charging system I think is good. It has a rewound rotor from Jim and I have a volt meter on my bars and it was charging while riding.
Battery is new from 1yr ago.
I found the original condenser and an aftermarket from fleabay I had purchased before I found the Nippon Denso one.
I have a capacitance meter around here somewhere to look at the condensers.

 

[Melnic]

Found the Capacitance meter. While mounted, the Denso condenser measures 244/253nFarads.
The original and the Fleabay ones are both 223/227 nF.
I don't have an analog Ohm meter but it seems the Denso charges up a tad slower than the others. Hard to tell with a Digital meter.
I'll pull the Denso one just to check out of circuit. But I'll put the fleabay or orignal back in. I know the original was working before I pulled it but it was exposed to a high battery voltage at one point (out of adjustment regulator).

 

[Melnic]

I now think its the battery.
It was 12.6 when I got everything back together.
On first press, it started up for about 2 seconds, then stopped.
Crank crank 2 more times, nothing.
Then I checked spark and nothing.
I have 12V at the points and rotated the engine to see my static timing is good.
Well, then tapped the points and no spark at the plugs.
Looked at battery and its 12.0V, It was dropping down quite low well below 10V when cranking the starter.
I still think it should have been running with the alternator powering the bike.

will charge it up and hook up to spare battery to run it but I think I'll table things after that till I can get a good AGM.
The AGM in my BMW works REALLY well, I"ll have to see if they have one that will fit this bike.

 

[Jan_P]

Well if Voltage drops it can be a Short circuit somewhere Pulling down a fairly good battery
..and is Consistent with a shorted alternator rotor ---and cutting out on the road applying of throttle gives richer mixture a weak spark cant handle.
Can be the battery but the Charging Voltage measured across battery would help
If no meter observing the Headlight intensity as revving up if getting brighter can give info if not maybe not charging

 

[Melnic]

Sanity check here.
If I have power on, and I have a plug grounded and hooked up to plug gap, I should be able to take the cooresponding point and open/close it and get a spark right? I'm not getting one.
I have 12V at the points when open and then 0V when closed. but tapping it open/closed won't give me spark.

Could both coils gone together? Or maybe its the ground that goes from the other end of the coil to the chassis?
Is there a way to test the primary and secondary of the coils?

 

[Its been a long time]

Sanity check here.
If I have power on, and I have a plug grounded and hooked up to plug gap, I should be able to take the cooresponding point and open/close it and get a spark right? I'm not getting one.
I have 12V at the points when open and then 0V when closed. but tapping it open/closed won't give me spark.

Could both coils gone together? Or maybe its the ground that goes from the other end of the coil to the chassis?
Is there a way to test the primary and secondary of the coils?

Yes there is. Best to confirm numbers but IIRC primary winding resistance of the coil should measure around 4.5ohms.

 

[Jim]

Is there a way to test the primary and secondary of the coils?

 

[Melnic]

thx all.
Coils are within spec.

I still swear I should be able to get a spark by manually opening points. I am pretty certain I've done that before.
Take the points that are closed then open them manually. This should toggle 12V on/off to the coils and the transition should cause a spark.

 

[Jim]

I still swear I should be able to get a spark by manually opening points. I am pretty certain I've done that before.
Take the points that are closed then open them manually. This should toggle 12V on/off to the coils and the transition should cause a spark.

Yep. The way I do it is turn the crank until that set of points is open, then touch the gap with a small screwdriver or similar. Soon as you remove the screwdriver, the coil should discharge.

 

[Melnic]

ok, this is going to still be a mystery but this is so weird that I think next time I'm working on the bike i"ll put my helmet cam on me recording.
So, I tried the method that Jim described above and NOTHING. NO spark. I had 12V on both points when I rotated the engine and the timing mark passed the F marks. I moved it so that both were in the open position. shorted out the points and nothing at all. I rotated the engine again to make sure it would go back to 0V at the points.
So then I was like hey, do I have a fuse blown? (did not think so since I had 12V at the points. I pulled the fuse cover off and there was a spare fuse loose on the side. Ok, that's wierd. I don't recall if I heard a click then or after I touched the points again, but sure enough when I manually opened the points, the plug I had hanging on the cap started to spark. Then I rotated the engine so the right points were closed and hooked up the spare plug to that side then manually manipulated the points for the right side and it was sparking. Put the tank back on and it started right up.
the spare fuse was sitting right next to the ignition fuse.

I am traveling this week and going out of town so I won't be able to test ride until likely Friday or Sunday at the latest.

For most of the day today, I had zero spark and it would not start.
At least I can end the day on a positive note.

I also at least cleaned ups some stuff that could use it and if it dies again on the road, I will have a volt meter and a spare plug with me and a JS screw driver to pull the points cover off and look to see what's happening.

I have NO IDEA how a bouncing around fuse could do this. I just know the sequence of events. Maybe its a coincidence but I'll find out next week.