Sudden loss of spark

[scott0757]

My 1980 XS100SG ran great when it parked it a few weeks back. Today I went to ride and would not fire. Not spark at the plugs. Seems odd but al the plug caps seem to have open resistance...cannot get a coil reading unless i pull the caps off and probe the leads directly. Primary coils read correct. Balkst resistor voltage onky reads about 5 to 6 volts and I read on her ut shoukd read 12. New battery. Going through everything...not a clue so far.
any ideas? Emergency Off switch? Thx.
ps. New 5ohm caps onn order

[Bax]

Broken strands inside of the insulation on the pickup coil wires are a known spark killer problem.


----Bax

[scott0757]

That's next on my checklist. Thanks

[scott0757]

Checking the pickup coil leads. One thing i found was the vacuim hose had split znd popped of the carb vacuum tube.
My colors are not what my Clymers diagram shows. I am assuming the Y and W stripes are the actual pairs.
Clymers. Actual
R/W. R/W
G/W. G/W
Y. G/Y
Y. R/Y

i measured 730ohms between Yellows and open between the whites. Not sure how I know which coil/wire these white wires go to. Where do these wires normally get spliced to new color?

Also the wire routes under the case right over the frame tube. Will be fun to find where I need to splice.

[Bax]

scott0757 Check out this guide.

https://xs11.club/forum/repairs/batt...il-wire-repair

Bax

[cajun31]

just throwing this out there ... but it could also be your TCI. Have you checked the connections going in and out of that?

[scott0757]

Cajun31-
I checked all connections first, including the TCI's. I have found intermittent pickup coil leads and fixed them and am mid-rerouting that harness under the case and up behind the fuse block. Working my way thru everything. The plug wire caps seem to be a real issue...open resistance. Just strange they all went together. New cap on order. Coil primary tests perfect. Plug side tests good when caps removed. Thx for suggestion.

[scott0757]

Got nice blue sparks on all 4 plugs, even those with what appeared to be open resistance plug wire caps! Go figure. Time to reassemble and test ride. Wonder if the disconnected vacuum advance line could have resulted in stressed coil wires?

[Bax]

scott0757 The flexing pickup wires have long been an issue. Good to hear your spark has returned.

---Bax

[bikerphil]

Probably too late, but this is the P/U coil wiring breakdown for a 79, may be the same as the 80...

https://xs11.club/forum/miscellaneou...2h7#post863762

[scott0757]

Just to confirm what you provided did match my 1980 XS1100SG wiring.