Topic: 750 starting/running issues

[lhemrick]

I have a 1977 CB750K that you can charge the battery and it will start but only after a few minutes of running it will not start back with the starter. You can kick start it and go where ever you want by kicking it over. I've ohm-ed the stater and field coils and they seem to be fine and I don't figure it would run if it wasn't charging so I'm left to wonder what the issue is. Also if you charge the battery and disconnect it from the bike it will hold a charge but goes dead if hooked up to the bike. Battery is about three years old.

Any help please,
Thanks

[jontc]

Sorry I cant help you with an answer, but had to say very cool bike.

[Sdsbassist]

IMO id start with a new battery. 3 years and they are about toast. Could be a drain somewhere on the bike.

+1 on having an interesting bike.

[scottly]

I have a 1977 CB750K that you can charge the battery and it will start but only after a few minutes of running it will not start back with the starter. You can kick start it and go where ever you want by kicking it over. I've ohm-ed the stater and field coils and they seem to be fine and I don't figure it would run if it wasn't charging so I'm left to wonder what the issue is. Also if you charge the battery and disconnect it from the bike it will hold a charge but goes dead if hooked up to the bike. Battery is about three years old.



Check the voltage at the battery with the motor running at 3000-4000 RPM; it should get up to about 14.5V (have the battery fully charged before you do the test). If it does get up to 14.5, turn on the headlight and see if it will stay that high, or if it drops. The battery going dead only when sitting in the bike might be a bad rectifier?

[lhemrick]

Thanks! Any way to test the rectifier?

Thanks

[scottly]

The rectifier can be tested with a meter, preferably one with a diode test setting. I believe Two-Tired wrote up a good tutorial; I don't know if it's in the FAQs or tips and tricks.

[lhemrick]

Found it. Looks like some good information. Since my strength is not in the electrics of these bikes this should help me figure it out.

Thanks,
Lynn

[lhemrick]

I've been through part of the list of checks down to the voltage regulator. At 4000 rpm the bike is not giving the 14 to 15 volts it should to the battery actually the voltage doesn't go up at all. I'm wondering do I go ahead and try to make the last adjustment to the regulator or could it still be the rectifier?

[lhemrick]

Took it out for a 10 to 15 mile ride stopping a half dozen time along the way and failed to start on the last stop. Kicked it and got it home battery was down to 10.23 volts.