Topic: CB750 electrical prob...

[wornknobby3]

ok, i picked up this 750 and it only has the bare minimums of wires, but i still don't have spark.
1. i tested the coils, they have around 23k ohms
2. i have the yellow, blue, black w/ white stripe, and green w/ yellow stripe coming from the points.
3. I cleaned the points, but can't gap them as of right now
4. the green w/ a yellow stripe i assume is for the taillight so im leaving it alone, and the other 3 go to their respective spots @ the coils.


sorry for such a long post, but now after that i have an On/Off switch w/ a lead that I'm running to the black w/ a white stripe of the coils and another lead to go to the positive side of the battery. Theres on other component, (not sure what it is), but it has a lead that originally goes to the battery. even w/ this hooked up i can't get the motor to crank, so i figured, what the heck, I'll just go w/ kickstart, but i still got nothing... does anyone see anything wrong w/ what I am doing, cuz i've tried and tried and just can't figure it out.

now i read the FAQ in another area, and i see u really can't run these bikes w/ out batteries, so, what my ultimate question is, what can i use for a bare minimum of components to get the bike to start?

(i have an entire wiring harness from a 76 cb750, but i cannot determine what some of the components are? so I'm not sure if their needed or not)

another thing is, can i test the points for resistance? the coils i can test, but I'm not sure what kind of readings I'm supposed to be getting

any and all help is greatly appreciated, thanx

[jsaab2748]

Do a search on this sight for a wiring diagram for your correct model/year.
The green with yellow stripe I believe should go to the brake pedal switch that operates the stop light. the blue and yellow wires go to the points, (and the wiring diagram will tell which color goes to which set of points). The black/ white wire I belive should be hot with the key on, and the handle bar kill switched to run. Never worked on a 750 without a battery installed and operational. And if the main fuse is missing or blown for whatever reason, you'll never be able to power anything up. I'd start with a battery, check the main fuse, then make sure everything's wired correctly, again, using the diagram. Once it's wired right, start checking for current at the points, then make sure they're adjusted to spec followed by timing adjustments. A lot can be learned by buying a service manual for your bike. It definately makes things easier. There may be more, so someone else will add..

[750essess]

ground battery to engine
positive of battery to kill switch to one terminal on both coils
yellow wire to other post on coil for 1/4
blue wire to other post on coil 2/3
it should have spark
i cant find a good diagram at the moment to confirm the wire colors, so they yellow and blue may be reversed.

[wornknobby3]

ok, thanx, i just ordered a manual so it should be here in a few days, but here goes another shot, this is what i have done...

I just tried what 750essess said and I'm not sure how exacttly or what exactlly, i'm doing wrong, but when i do this, i do get a small "spark" as i connect the wires to the battery, but as far as getting a reading of voltage from the plug caps I'm not getting much,

so far this is what i have...

From the rectifier there are 5 wires: 3 yellows, green, and a red
- the 3 yellows go to the connector which enters into the case
-the red turns into the red w/ a white strip @ the connector and goes to the magnetic motor starter and the fuse box.

The magnetic motor starter has a ground which exites out from the case, a yellow w/ a red stripe and a green w/ a red stripe.
-the yellow w/ a red stripe goes to the ON/OFF switch. ( I have a single on/off toggle switch as of right now)
-the green w/ a red stripe goes to a small aluminum finned device.

From the small fined aluminum device the green w/ a red stripe slices and goes to the connector which enters the cases
-the white wire from this device does the same

from the voltage regulator the white goes to the connector into the cases and the black goes to headlights??? or some type of lighting?, not sure on that one.

from the ON/OFF switch i have the yellow w/ a red stripe which goes to the motor starter and a red wire going to the fuse box which comes out in the other end being the red w/ a white srtipe.

wheew, that was fun, but now, I think  I'm missing something as i still can't get the bike to crank over, if any one was even just willing enough to read this post, i thank you, any and all of your help appreciated.

[750essess]

What I told you was just to get the spark running and kick starting. Go by the wiring diagram when you get it to hook up the rest of it. Also I wouldn't try to measure volts at the cap its very high voltage, just put a sparkplug in there and ground it to the engine to see if it sparks.