Topic: CB750k5, Electric cuts out while riding, then comes back on. Strange!

[tonevault]

Recent purchase, and the bike runs good.  Battery is strong, and most electrical seems fine.

...except the past few times I've ridden, the bike will shut down (all electrical) somewhat randomly.  I have been able to open the seat, wiggle the battery connections, and then re-try.  Lights come on, bike starts.

Re-tightened battery connections, and test drove....  It cut out again.  This time, I just sat for a minute and re-tried.  Lights came on, bike starts. 

Last couple times I've ridden, it's cut out more frequently.

Very odd, as it is only "off" for a minute or two, then it works again.  I suspect this will be an increasingly common occurrence, and it needs to be addressed!

I checked the SOHC database, and found some good info, but nothing that quite matches the problem.  Do you guys have any wisdom for me?

Thanks in advance,

Greg Ernst
Long Beach, CA
Stock CB750K5

[scottly]

Take a look at the ignition switch and it's wires.

[TwoTired]

If you can wiggle stuff and make the problem come and go, then the problem is where it is most sensitive the wiggling.  Corrosion, broken wire, bad crimp, bad fuse contacts, bad fuse, bad key switch, etc.

You are going to have to localize the problem, or replace everything in turn, until the problem stops.

Got a multimeter?

[Johnie]

Start with the easiest thing to eliminate. Had that same issue and it was dirty contacts in the ignition switch. When it happens again rotate the key back and forth a few times and see if it comes back on. If you remove the rubber on the back of the switch you will see some holes. That is where I sprayed the contact cleaner. If you decide to get a new switch hesitate from getting an aftermarket like Emgo. There has been a number of guys here that have problems with that brand. You can stil find the switches around. Good luck and let us know how you come out.

[stickman]

+1 on the switch.  Pull it for inspection, cleaning, repair or replacement. 

[XLerate]

Something else I've found on numerous vehicles and especially where you are, near the ocean: hidden corrosion. You might want to take a real sharp kife and skin back the plastic insulation where the main electrical cables terminate with battery lugs. Just a short little cut, enough to expose the wire underneath. If you see green corrosion deep down between the strands of the wires they need replacement, not cleaning.

Also being as it's intermittent it would be good to clean and tighten all the electrical connections you can get to, in case something's loose, making poor contact.

[bjbuchanan]

Could also be a fuse that is shot sometimes the filament looks good but isn't.worth a look before killing yourself. others have had it happen myself included. It is from the vibration

[tonevault]

Ok, guys.  First, thanks very much for all the input!  I pulled the ignition switch, and gave it a thorough cleaning with electric cleaner spray, reinstalled.  Also pulled the starter/kill switch assembly, and gave it a thorough rinse with the spray.  Ran it for a few miles, and it stayed on!  Seems like a lot of gunk came out of the two switch assemblies.

I will give it a more thorough test drive later, or over the weekend, and let you know how it sorts out.

Thanks again!

Greg

[74750k4]

Does it happen "at speed" or at idle???

[tonevault]

Both!  It does not seem to be a charging issue, seems to be random.....as if a connection is just cutting off.  Then, it seems to reconnect on its own after a moment or two. 

[m13]

My cb500k3 77" did exactly the same, hotwiring regained the power back and 2 prongs of 5 in the contact was very loose and the plastic that holds them got cracked when I wiggled the prongs.
(at least that's what i think is wrong haven't confirmed it yet I have ordered a new aftermarket ignition switch repair kit, but can't change it the bike is stored in another town over the winter.

[scottly]

Both!  It does not seem to be a charging issue, seems to be random.....as if a connection is just cutting off.  Then, it seems to reconnect on its own after a moment or two.

Hmm, you mean it turns off and on like a switch?

[nikcorg]

I got stranded last summer with the exact symptoms you describe, which turned out to be a very corroded ignition lock. It was so bad, the extra resistance it caused melted my fuse box, as well as burning through a few 15A fuses before that. I replaced the ignition lock and mostly everything electrics related has been working since.

[Grabcon]

My kids CB550 had a bad fuse box. The fuses were lose and would not stay in contact causing the bike to die while riding. Remedy Replace fuse box with new style to accept blade fuses.

[74750k4]

Yes, high resistance at any contacts causes extra heat right there, but not in the rest of the circuit, it's getting colder, not hotter. So for example, fuse contact resistance increases, and gets hotter right there, but cooler switch contacts in that same circuit result, and vice versa   The current is always the same, in every part of the series loop. So hot contacts in one part of the circuit, do not burn out other parts, (unless they are touching the burning). High resistance contacts are actually reducing the current through that entire circuit, while they get hot, and are burning up. Once they completely burn up, the current is reduced to zero, or close to it. Then the whole circuit gets cold, and that circuit is dead. It can cool off and make contact again too! Which starts the whole process over again

[tonevault]

Thanks for all the great tips and experiences, guys!  As I mentioned above, after a thorough cleaning of both the ignition switch assembly, and the kill switch/starter button assembly, the bike seems to be running consistently again.  Several trips, and no more stalling so far. 

Let's hope it stays solid.  Be safe out there, and thanks again!

Greg