Stuck! Can anyone shed some light?

[cstaud1]

I have been having a problem with my '78 XS11. Thought it was the common pickup coil problem but it seems like that is NOT the case.

It seems like intermittent spark failure. When starting, I either have great spark or none whatsoever, determined by a spark checker on cylinder 1. If I have no spark, I can cycle the ignition switch a few times or wait a few minutes and it will come back, strong as ever. Occasionally I can witness a spark being missed every few revolutions or so, but usually if spark is present, it is sparking strong and consistent.

While the bike is running, it will run like a champ, until this problem rears its head. When it occurs, the bike will start backfiring, and experience a MASSIVE power loss. If I pull the clutch, and come off the throttle, the engine will die. I can use the motion of the bike to "push through" the problem, eventually I will have a massive return of power and the bike will run normally again for awhile.

The problem only appears at city speeds, if I'm doing 75 on the highway, there's no problem whatsoever.

I thought it was the pickup coil problem, but all the wires check out OK, and moving or tugging on the wires has no effect on whether or not spark is present.

Any ideas? I'm not entirely sure where to start. I've take the kill switch out of the equation, and thoroughly tested the ignition switch. All check out great.

Thanks for any help! Appreciate it!

[DiverRay]

I would start with all the GROUND connections. Loosen and tighten them all, and put de-oxit or anti-seize on ALL the ground points. This is battery negative, frame, frame to engine, and the wires on the Reg/Rec hold down bolt.
Next would be the ballast resistor. you can bypass it to test by connecting the two red/white wires together and running it for a LITTLE while. Just be sure the wires do NOT touch ANY metal, as the bike WILL die!!! DAMHIKIJK
report back, after this testing, and we go from there.

[TopCatGr58]

Hey,

Aside from the KILL switch, have you taken the main key ignition switch out/apart? You can separate the wire/contact plate from the switch, inspect for corrosion and clean, grease, and reassemble. I say this because of your statement of wiggling the igntion switch and it behaves better.

You said the PU coils are not the problem, but didn't elaborate on your diagnostics. Plus most of the time it's not the actual PU coils, but the wires in the timing cover that go to and from the coils that break and cause intermittent contacts and come/go of spark energy! Have you followed the PU coil diagnostic process in the tech tip....pull on all wires vigorously???

And what does your fuse block look like? OEM glass fuses/holders, or newer ATCO solid fuses???

T.C.

[crazy steve]

Plus most of the time it's not the actual PU coils, but the wires in the timing cover that go to and from the coils that break and cause intermittent contacts and come/go of spark energy! Have you followed the PU coil diagnostic process in the tech tip....pull on all wires vigorously???

Yep, the pickup coils can check out good in a static/no load test, but on the road will cause just what you're describing... check for broken wires.

[DAVINCI]

Along with all the good advice above:

1. the ends of the plug wires can corrode, clipping 1/4" off and re-attaching them solves that. The plug caps screw into the wire cores.

2. The TCI box pins can corrode inside the box at the solder joints. re-solder ALL 12 (not just the pickup pins)



Oh, and:

3. there is a junction / plug behind the fuse box where the pickup coil wires joint the rest of the harness. Clean that plug up too.

[BowlingSS]

Still having the problems?

Bill

[Ken Talbot]

Before you move away from looking at the pick-up coil wires, be sure to open up the crimp fitting that holds all the wires together just before they exit the case. This will enable you to check that critical inch of the wires where they go through the crimp, through a rubber grommet, and out.

[cstaud1]

Hey all, sorry about my terrible forum etiquette, I got it in my head I already posted how things turned out, so apologies for the late reply.

In the end, I think Davinci wins it. There was damage to some of the solder pin connects in the TCI box, resoldering those seemed to have done the trick! In addition, I re greased and tightened all the ground connections, cleaned most electrical connectors, and thoroughly checked the wires coming off the pickup coils. After all is said and done, the bike seems to be great electrically! Powerful, consistent 20Kv spark.

Thanks again for all the help!

[Prothec]

Thanks for coming back and following up, especially from all of us lurkers