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Old 03-03-2013, 01:54 PM   #1
toothy OP
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No spark, intermittently 1970 CB350

Does a coil fail in an intermittently manner, or is the occasional because of a bad wire?


Thanks.
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Old 03-03-2013, 02:22 PM   #2
nulluser
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Both coils or just one side? If both coils drop out, it's something else, a bad ground perhaps.

The coils and condensers fail when hot on those in my experience, but anything is possible.

Put the continuity tester on each segment and giggle everything. You should be able to locate a bad connection fairly quickly.

You can also power the system from a car battery to make sure the charging system is not fooling you. The ignition on those bikes will fail weirdly when the voltage gets low.
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Old 03-03-2013, 02:28 PM   #3
matey peeps
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You bet they can. A slightly higher than spec resistance level in one of the coils can get even higher with as temp increases, disabling it. Vibes can effect them too. Crummy connections and bad grounds are also considerations.
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Old 03-03-2013, 06:13 PM   #4
toothy OP
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Just the one side misses spark on occasion.

On this bike the coil and spark plug wire is unitized. I think I'll spring for a new aftermarket set.
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Old 03-04-2013, 02:11 PM   #5
ibafran
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If there is a condenser for each set of points, one might be bad. Timing light should show the spark moving back and forth on the timing marks for the bad condenser.

Burnish the points with a business card.

Hose the high tension lead (spark plug wire) down with WD40 in case the spark is bleeding off down a dirty/cracked wire.

Swap the coils and see if the fail moves with the coil.
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Old 03-04-2013, 02:15 PM   #6
emti
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I vote for a bad wire/connection, If a coil goes bad its usually not a "miss". Make sure all is clean, oil free and tidy under the points cover. emti
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Old 03-04-2013, 06:06 PM   #7
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Coils do go bad, but it is unusual. More likely the points, condensers or the plug wire or cap. I would clean the points and make sure that the plug caps have good contact with the plug wires. That connection gets worn and fails regularly.
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Old 03-06-2013, 02:34 AM   #8
assquatch20
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I'm going through the same on my CL. Thing is, everything is nice and new except the coils for me. Wrung it out on a stretch, started stumbling when I came back down. Seems like everybody loses the left cylinder spark. Coils go on this bike more than others.

From what I can tell, XS650 coils are a good replacement, from here. Just takes a little tweaking to bolt up, nothing crazy at all.

Read this for a little more insight. Sounds like coils, but check condenser, points, and plugs as well.
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