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Author Topic: Possible Ignition Issue: SOHC CB750. Help, wizards?  (Read 184 times)

Offline ChroniclyQuickly

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Possible Ignition Issue: SOHC CB750. Help, wizards?
« on: Jan 09, 2017, 02:02:36 »
I'll try to make this brief and skip the incidental details. Basically, my ignition cable #4 was compromised but was still working fine so I took the bike out. 10 mins into the ride, suddenly it began backfiring and running very choppy, very herky jerky. The bike idles just as well as ever which is too fast but a different problem all together. But when I open the throttle, that's when things get sloppy.
Before you ask, yes I tried removing cable 4 and the bike did run much worse, the problem is not isolated to a dead cable, the cable is still providing at least some spark.
I'm assuming the cable arced on my ride. What could be the problem, how can I test that (yes I have a voltammeter) and how might I resolve it?
I'd much appreciate some wisdom, I'm not new to bikes but I am not electrical literate nor experienced with internal engine mechanics. I can change a part if I need to, I'm not even sure how to find the part that needs changing or if the problem may be more simple. The bike has just over 10k miles, fantastic condition over all.
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Offline Cookie

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Re: Possible Ignition Issue: SOHC CB750. Help, wizards?
« Reply #1 on: Jan 09, 2017, 08:31:22 »
I'd look into the lean condition causing your high idle first. The same air leak can cause acceleration nightmares.
 Weak battery/charging system; cracked ignition wire(s). A bad coil or wire may run fine at idle, but as you increase load it'll break down and lose spark.

Hope this helps
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Offline focusinprogress

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Re: Possible Ignition Issue: SOHC CB750. Help, wizards?
« Reply #2 on: Jan 09, 2017, 09:35:05 »
A bad coil or wire may run fine at idle, but as you increase load it'll break down and lose spark.

In addition to this as the wires heat up the resistance is changed and they become more likely to arc. chances are the compromised wire is barely working when the bike is cold, and then as it warms up it begins to arc worse and worse. replace the wire, or remove the cap and do a couple layers of shrink tube over it and put the cap back on and then run it with the lights off and watch for the arc.

once that's settled definitely investigate the high idle issue.

Offline ChroniclyQuickly

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Re: Possible Ignition Issue: SOHC CB750. Help, wizards?
« Reply #3 on: Jan 09, 2017, 17:07:16 »
In addition to this as the wires heat up the resistance is changed and they become more likely to arc. chances are the compromised wire is barely working when the bike is cold, and then as it warms up it begins to arc worse and worse. replace the wire, or remove the cap and do a couple layers of shrink tube over it and put the cap back on and then run it with the lights off and watch for the arc.

once that's settled definitely investigate the high idle issue.
I'm trying not to give my hopes up but I hope you're correct and once a new cable goes on, it works. If not, I will be able to at least eliminate something. In your opinion, if the problem is not isolated to the cable, what do u think is the next mostly likely option?


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Offline Cookie

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Re: Possible Ignition Issue: SOHC CB750. Help, wizards?
« Reply #4 on: Jan 10, 2017, 08:01:51 »
If it's not a single bad wire, you're likely looking at a bad coil or an air leak.
Also check your battery (run a proper load test). A weak electrical system will also make the machine run like crap.
"I fear the day that technology will surpass our human interaction. The world will have a generation of IDIOTS."

Offline irk miller

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Re: Possible Ignition Issue: SOHC CB750. Help, wizards?
« Reply #5 on: Jan 10, 2017, 09:50:04 »
Testing coils, plug wires and the electrical system is easy to do.  I'd run through it all with a meter.  The charging system is a known weak point, so testing that wouldn't hurt either.