Topic: Zap - Electrical Problems

[Canuck Cafe]

Hi Guy's,

Sorry in advance for the length of this post, but if anyone's patient enough to read through it and provide suggestions I'd be really, really, grateful it going to be a nice weekend and I’d love to be able to go for a ride.

I took my 1975 CB750 for a long ride last week and at the beginning the bike was running terribly.  I had very little power and it seemed sluggish, but after riding for a bit it seemed to clear up and run ok, so I didn't think about it since.
 
This week I did some cosmetic work on the bike by replacing the stock signals with shorty aftermarkets and I also put on a set of clubman bars.  After the work was completed, I started the bike and it ran terribly for a minute or two and then died suddenly. I pulled #4 plug and set it on the engine block to see if I was getting spark and I wasn't getting any.  I then decided rather than pulling all of the plugs, I could put a strobe on the wires to see if they would light up the timing light….and nothing.  So no spark at all.  I pulled out the Ammeter to check continuity on the kill switch across the switch itself and it's fine. I've checked for loose connections and can't find any.  I've checked the fuses and they are all fine.  The bike has a battery that's about a month old and has 12.1V on a load test, the motor turns over and all of the lights are strong.

I don't know if I caused anything by replacing the bars and signals, but here is exactly what I did:

The new signals are three wire, so the ground wires of the new signals were not used and taped off.  They are grounded through the headlight shell.

When replacing the bars, I had to slacken off the clutch cable all the way to get the levers on the new bars. The throttle grip and kill switch slid off the old and onto the new bars.

I now realize that when the bike was running poorly on the ride last week it may have been running on two cylinders.  After replacing the signals and bars, it may have also been running on two cylinders, but this time it died completely, rather than clearing up.

I have to readjust the clutch cable because right now it’s not completely disengaging even when pulled in. Is there a switch in the clutch that only allows the bike to start with the clutch disengaged?

I ran a wire directly from the positive terminal to power the ignition coils, and am not getting any spark.  Is this bad coils?
 
Could this be a bad ground causing no spark and if so where should I check?

What other things should be checked causing no spark?

If I can check anything that will help with diagnosis, let me know. Thanks!

[Canuck Cafe]

One more thing ... I just checked the battery again and its voltage is 11.69, is this enough to fire points ignition and could this be bad condensers?

[eldar]

Charge your battery back up. Check out your points to make sure they are closing and opeing properly. If they do not open/close, then spark can not occur. I think gap is .012 - .016 for the points when fully open. Set those then pull the 4 plugs and shut off gas and crank it over and see if any plugs get spark.

[Canuck Cafe]

Charge your battery back up. Check out your points to make sure they are closing and opeing properly. If they do not open/close, then spark can not occur. I think gap is .012 - .016 for the points when fully open.

Thanks, the battery is on charge. Checked the points and they were tight.  They were .008 and now adjusted to .012.  Also, the surface of the points are not perfectly flat.  One one of them, the one closer to the front, has developed a small nipple on one side and a corresponding depression on the other.  Will buy some new ones...

[STLrocker]

once your battery is charged. you need to start working your way back from the coils.

first you can check that the points are working and they are getting proper ground.

then, with the key on, check the black/white wire for 12v just before the coils. then check for 12v just before the kill switch. then after the kill switch. from there it just goes to the ignition switch. so you can check it coming out of the ignition switch. if you dont get 12v at any one of these points stop and find the problem ( broken/ loose/ grounded wire) between where you are, and the last place you saw 12v.

it dosent seem like a fuse issue cause the main fuse is before the ignition switch, which means you wouldnt have lights without it. it also dosent sound like a cuch safety switch cause that stops the starter from working, not the coils.

i would think that since you were working on handlebars/signals, it would be the kill switch wiring or something i the headlight bucket.

if you dont have a wiring diagram you will need to look at one to know what youre looking for. here is a good one. you can hilight only what you need. http://oldmanhonda.com/MC/wiring750K1.html  it's for a k1 so it's got a few differences. the ignition circuit is the same though. the signals are different in that the fronts will have an extra blue/white and orange/white for running lights.

[750k5]

If you did all that work, and the bike did start up, I would think the kill switch is not your problem.  By the sound of your description, the points could very well be the culprit.  New points, and set them to .016, when they wear they will only close more, so start out at .016

[TwoTired]

I pulled out the Ammeter to check continuity

Er, ammeters measure current.  Ohmmeters measure resistance or continuity quality.

For troubleshooting the ignition:
VoltMeter probes black and Red right?
Use voltage scale.  Turn on ignition; kill switch in the RUN position.
Black lead on the breaker plate.
Verify Blk/White to the coils have 12V
Reconnect Blk/White to the coils.
Verify Yellow wire from coil (wire to points disconnected) has 12V. If missing voltage replace coil.
Verify Blue wire from coil (wire to points disconnected) has 12V. If missing voltage replace coil.
Stick thin balsa or thin card board between both point contacts, both points
Reconnect yellow and blue wires at points.
Verify 12 v at stud terminal of both points.
If 12 v missing, disconnect condenser and wire from points stud.
Verify 12 v at disconnected wire end Yellow and Blue.  If either missing voltage find break or ground in wire between coil and points.
Reconnect only the wires to the points stud.
Verify 12 v at stud terminal of both points.  If either missing voltage replace that points set.
Reconnect condenser to the points stud.
Verify 12 v at stud terminal of both points.  If either missing voltage replace the condenser.
Remove card board between points.
Verify 12 v at stud terminal of both points when open. And zero V at stud terminal of both points when contacts are closed.
Run bike.

The new signals are three wire, so the ground wires of the new signals were not used and taped off.  They are grounded through the headlight shell.

Only if they still have a connection to the green wires in the elect harness.  The the Headlight buckeyt is connected to the upper fork covers that are rubber isolated from the forks and frame.
Those turn signal grounds should connect to the green wires in the harness bundle in some way.

Is there a switch in the clutch that only allows the bike to start with the clutch disengaged?

The electric start should work with either clutch disengaged, or the trans in neutral.  Neither of these interlocks effect ignition circuits.  Kick start whenever.

Cheers,