Topic: No Spark 1976 CB750

[ic455]

Just got a non-running CB750 from a friend.  It used to run fine and I have ridden it.  He says that he went for a short ride, parked it; and it rained that night.  Next day bike won't run.  Electrical system is hacked to pieces, starter is inop, only kick will start it.  Has an aftermarket ign. switch.  I hooked bike up to battery to check wiring, have power at points (only when open) and power constant at black/white wires at the coils.  Still no spark when plug is inserted into wire and grounded (and bike is kicked over).  My thought is bad coils.  Any ideas?

[Bob Wessner]

He says that he went for a short ride, parked it; and it rained that night.

How long ago did it get wet? Could still be some water in there somewhere, particularly if it's a home brewed harness. You could try removing the covers, tank and open the headlight shell and get a fan going or park in the sun for several hours with the everything exposed. Maybe a long shot, but might be worth a try.

[Gordon]

Both coils rarely go off at the same time.  If you have power up to the coils, it's probably either the plug wires, the plugs, or possibly the condensers.

[ic455]

Man, talk about quick response!!  It's been a couple months since it got wet, if it got wet, he said it rained but I don't know if the (torn) bike cover was on or not.  Headlight is the only functional electrical accessory.  I'll check out the condensers.  Thanx!

[SohcCBs]

If you want to keep this bike, I highly recommend you either get a new harness or rewire it from scratch.

[ic455]

If you want to keep this bike, I highly recommend you either get a new harness or rewire it from scratch.

Yeah, that's what I've got planned for it in the future.  It's really not roadworthy but was being ridden anyway.  I plan to do some major restoration to this bike before I get serious about riding it.  Thanks!

[SohcCBs]

When I first got mine, I spent about 30 minutes troubleshooting the electrical........and then stripped the bike of all wiring.  Then rewired it myself with all 12 guage wire.....10 gauge on the grounds.



Now, 6 years later, it's not as pretty (time to paint again), but it runs like a banshee.

[ic455]

That sounds like the best bet, this bike's wiring is a mess.  I'll get some pics of it on as soon as I find my digi cam.

[ic455]

It lives!!  Looks like it was a bad connection at the coils.  I decided to double check all the wiring at the coils and found a loose butt connector.  I guess the coils were getting 12v sitting still but when I was kicking it the connector was breaking contact and causing a no-fire situation.  Now I just gotta get it to stop smoking!!

[SohcCBs]

Congratts!!  That's persistance.  Sometimes it helps to walk away for a while, and come back later.

[ic455]

Congratts!!  That's persistance.  Sometimes it helps to walk away for a while, and come back later.

Thanks!  A little break from a tough problem is always good, but even better when it includes some supper!

[dusterdude]

groovy