Topic: CB750 - lost 2.3 volts between battery and points - Great an electrical issue

[Ace]

Hi all, Just put my engine in and I thought I'd check the timing like I always do. The light on my tester didn't light up when connected to see where the points opened. Tested the light across the battery, nice and bright. Checked voltage across battery 12.7, checked at where the points plate wires plug into the harness near the oil tank, 10.4 volts at both blue and yellow wires. From searching/reading seems I'm down a lot. Battery was fully charged. Tried again at night, the light shone dimly, adjusted the points plate to open at the F mark all good. Didn't fire it up as it was late at night.

As I said, fully charged battery, standard coils, Hondaman ignition (IGN or PTS switch gave same voltage so not that). I'm loosing 0.5 volts just through the key switch itself (red in and then test black out at the plug) and is isn't that old. I hate electrical issues unless someone tells me it's all good with the drop in voltage. I have replaced a few power wires that were looking dodgy, not the black one the runs in the harness and branches out to various things. So between the start of the branch before the coils and through to the blue and yellow wires where the points plug in I'm loosing a lot of volts. Any ideas or am I just going to have fun with a multimeter while I'm on holidays? Cheers.

[seanbarney41]

since you've had the engine out, make sure you got a really nice clean ground, other than that sounds like you have checked all the usual suspects...maybe just double check everything is tight and clean.  I would say 11 volts at the coils is pretty typical and will run ok with these old bikes but the more volts the merrier.  Also, might try fileing/cleaning/replacing points, as I have had problems with dirty points failing to light a test lamp before.

[mystic_1]

Regarding using a test light to statically time the points, put a piece of paper into the set of points you're not working on.  I just ran into this yesterday.

As far as your voltage drop, have you checked all of the bullet connectors in the circuit path to make sure none of them have excessive corrosion built up?  That's a common problem.  Clean them up with steel wool.  To clean the female connectors, roll a bit of wet-or-dry sandpaper into a small cylinder.

mystic_1

[Ace]

Got the contact cleaner out, cleaned up all the connectors (some actually looked clean until I sprayed and wiped) and gained 0.7 volts so now I have 11 volts at the points. Got the rest of the bike ready and first press of the button after a few seconds it came to life, sounded better than before too. I'll work with 11 volts, I reckon I could get more but that would entail time and wiring. It is 44 years young the wiring  Thanks guys.