CB750 scrambler project

[Louis-DT-WR]

@Calum thanks, I'm pretty sure both coils are bad. No resistance at all between power/trigger and the caps.

They were second hand, came with the loom.

12.8 volts on the looks power connectors.

New coils, leads and caps on order

I

[SpookDog]

Wasted spark is when they both spark at top dead centre?
Have you not gotten any old coil off of another bike? Even a single one that you can get to spark? It would at least prove the rest of the circuit was on par...

[Louis-DT-WR]

@SpookDog yes wasted spark system is that.

I've ordered new coils as the primary has 3 ohms which is fine but secondary resistance has no resistance at all. On both. This is 1 fault. I'll have to see if there is others.
They are very old and probably corroded inside

[Louis-DT-WR]

This is the confusion I have , electrics are not my strongest point.

The manual says the yellow/blue wire goes at the top connector on both coils...

The coils are not handed so the green terminal is at the top on one side and black at the bottom when installed.

That's a what's confusing me
I'm still waiting for the new plug caps to try.

I'm also not sure if I need to loop the sidestand indicator light as I removed it... I'm pretty sure it just piggybacks

[SpookDog]

If it’s connected to the ignition it could be the cause of your problem, specially if you’re neutral lights not working...

[Louis-DT-WR]

@SpookDog

Do you think that's the problem looking at this?

To me it looks like if the neutral light is on (which it is) it should start.

[Calum]

So it looks like according to the diagram that the G/W wire needs to be tied to Earth if you want to bypass the side stand switch. The Y/Bl wire can just be taped up. I.E. don't complete the circuit for that.

[Louis-DT-WR]

@Calum I have the sidestand switch, all plugged in. Only the indicator light isn't connected. Does that affect it? Cheers.

Also still confused on the wires to the green or black connectors on the coils.

[Calum]

The light only needs to be there if the side stand is down by the looks of it.

[Louis-DT-WR]

@Calum that's what I'm thinking but if in neutral then it shouldn't Matter ,?

[SpookDog]

I can’t get my head round the diagram at the mo. There are a lot of differences from what I know. What about the diode (number 7) condition?
I know that the live wires on the coils will only affect spark timing if wrong, they should still spark. So I’m guessing that the problem is with the side stand, neutral, cutout circuit somewhere, if there’s no spark still...
Sorry I can’t be more help at the mo’. Too many brewskies!🤪

[Louis-DT-WR]

@SpookDog yes it's a crappy diagram, I assume the second bulb is the neutral one.

I've never had a diode go wrong on anything but might test it.
I think it's the side stand ... I'll do more tests when the plug caps come.

Thanks

[Louis-DT-WR]

@SpookDog I think if I try to crank the engine over (on the starter motor) in gear but with the clutch switch pulled in... That would also prove if the silicon diode is faulty

[SpookDog]

A diode only lets electric pass one way I think. I’d try a continuity/bulb test

[SpookDog]

Yeah, it should only show continuity one way. Do a quick google for diode testing...

[Louis-DT-WR]

@SpookDog thanks.. I tested the resistance and compared it to my spare one, seemed fine. I'm pretty sure it's the sidestand circuit....

[SpookDog]

I recon it is as well. I’d connect the side stand and clutch switch stuff all up, put it in neutral and try it with the clutch pulled in.
With the coil connectors, I’d try one ‘one way’ and the other the ‘other way’ if that makes sense? One of them should spark. Once they are sparking it’s easy to figure out which is the outer banks and which is inner...
Good luck my amigo!

[SpookDog]

a Diode is like a one way valve for electric. The live wire on the anode and earth on the cathode should have continuity (power flowing through). Reverse the wires and there should be none.

[SpookDog]

One other thing! Are the coils making a good earth to the frame? I don’t mean the black &white killswitch wires. I mean where the metal bolts to the frame...

[Louis-DT-WR]

@SpookDog pulling my hair out,
All the diode does looking at the diagram is. When the stand is down and the bike is in gear, it won't start unless the clutch is pulled in .... But surely is shouldn't allow the starter motor to operate as that alone can knock the bike off the stand,

Also should the side stand light only come on when stand is down ( in gear )or all the time including neutral