CB750 scrambler project
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I'm not very familiar with this bike or twin terminal coils.
Bike won't start, I believe it's electrical problem.
No spark.The CDI I bought might be the problem.
On the coil it has 2 electrical connectors (both +) and earth's to chassis.
Ignition on and kill switch to run the voltage on 1 terminal (yellow and blue wire) to both coils has 12v.
But there nothing on the other 2 black / white wires. Not even when cranking over.
Surely there should be 12v to both terminals? -
Depends where you are measuring from. The coils job is to take the 12V DC and step it up to 20KV. So you measuring at 12V is outside the scopes range.
12V isn't enough to jump the spark plug gap.
Measuring Coils is usually done through impedance test on the primary to secondary, secondary to spark plug cap. Should fall within the tolerances outlined by the manufacturer.
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This post is deleted!
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Its a wasted spark system btw
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Depends where you are measuring from. The coils job is to take the 12V DC and step it up to 20KV. So you measuring at 12V is outside the scopes range.
12V isn't enough to jump the spark plug gap.
Measuring Coils is usually done through impedance test on the primary to secondary, secondary to spark plug cap. Should fall within the tolerances outlined by the manufacturer.
@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
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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...@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 -
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
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If it’s connected to the ignition it could be the cause of your problem, specially if you’re neutral lights not working...
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.
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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.
@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.
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@Calum that's what I'm thinking but if in neutral then it shouldn't Matter ,?
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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!🤪 -
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!🤪@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
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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!🤪@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
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@SpookDog thanks.. I tested the resistance and compared it to my spare one, seemed fine. I'm pretty sure it's the sidestand circuit....
