Topic: No Spark

[cafedad]

First, let me start by saying I am fairly sure this question has been asked a million times here and although a recent post suggested reading related articles on my topic (which I did) I still have not solved the problem.

I have recently acquired a CB750. I believe it is a 1975 but not sure.( No title and all)  I'm hoping some of you out there can help me out. The engine number is CB750E 2535994. The frame # is CB750F-1019272.

The bike is in pretty good shape but I have no spark. I have not yet gotten a manual because I'm not sure of the year.
The previous owner did some sort of chop job to the wiring so in the mean time riddle me this......

There is a black and a black and white wire coming from the shut-off switch. The black and white goes to the coils but what should be coming in on the black, 12v? This seems like it would be bad because 12v would be flowing to the coils. Or am i off thinking that?

Maybe someone could walk me thru the flow of volts. Example: 12volts flows in black thru shut-off switch. Moves thru switch thru bl/w wire to coils. Flows thru coils to points. Points gapped at .016. When points close grounds coils. Points open field collapes.

This may (and probably is) way off but if someone has the time it would be much appreciated along with any other help.

Thanks

Cafe

"Beer is proof that God loves us."

Ben Franklin

[Jonesy]

Refer to this post on the complete circuit. It applies to any year CB750: http://www.sohc4.us/forums/index.php?topic=12831.msg123560#msg123560

Maybe someone could walk me thru the flow of volts. Example: 12volts flows in black thru shut-off switch. Moves thru switch thru bl/w wire to coils. Flows thru coils to points. Points gapped at .016. When points close grounds coils. Points open field collapes.

This may (and probably is) way off but if someone has the time it would be much appreciated along with any other help.

No, actually you summed it up exactly right!

Looks like you have a 1975 CB750F, although you should have an "F" in the engine number as well... The serial numbers for that year were: Engine #: CB750FE-2500004, Frame #: CB750F-1000002

[OldSchool_IsCool]

CafeDad,

Check out the interactive wiring diagram at www.oldmanhonda.com

The diagram may not be 100% (depending on year, exact model and PO (Previous Owner) mods.

Try this link:

http://oldmanhonda.com/MC/wiring750K1.html

If that doesn't work, then goto www.oldmanhonda.com, click Motorcycle, click Interactive Wiring Diagram, click CB750.  Then, in the box near the bottom, turn off all systems except COIL.

[cafedad]

Thanks for all the help. The one issue I was not considering is the "waste" spark feature of the coils. If I don't have 1 and 4 (or 2 and 3) grounded I will not see spark. I don't think I have broken anything yet but the night is still early.

Thanks

Cafe

"Beer is proof that God loves us."

Ben Franklin