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No spark but all looks OK


Cumbria John
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I restore old motorcycles as a hobby and have a good deal of experience, but this one has me stumped. It is a CG125 K1 kick start only 6 volt, a fairly straightforward machine on the face of it. My problem is that I cant get the thing to spark. I have checked the ignition components as per Mr Haynes.

Points set and checked - rectifier new and checked (shouldn't come into the equation anyway ) - coil checked - condenser checked - generator checked, and all earths checked. I cant find out what the cranking output from the generator is, to see if there is enough charge coming from it (remember its a kick start only model and Mr Haynes only gives specs at 1000rpm and I cant kick it that fast ! ) I am not convinced that the rough and ready check using a test bulb is good enough.

The battery operated components - indicators and horn are all good, but they are on a separate circuit

What have I missed ? Any electrical wizards out there !!

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Hi. Checked the Ht lead and it is OK. Gone over it all again but found no faults using Mr Haynes' checks . I found a site giving checks with a multi meter and think that the low tension side of the coil is outside the given ohm parameters although it passes the bulb and battery test. I have now ordered a new coil to see if I am right. As an aside - I found lots of retailers offering 6v coils for CG125s but all were out of stock except one.So the freight restrictions because of Covid seem to be hitting us now.

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Looking at the wiring diagram when the ignition switch is off it stops spark by grounding the ignition system through a black/white wire. To rule out something funny going on in the ignition switch you could try disconnecting that black/white wire and make sure it doesn't touch anything and check if you've got spark. It's not likely to be the issue but if you can get access to that black/white wire it's an easy thing to rule out

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Guest Swagman

Hi. Checked the Ht lead and it is OK. Gone over it all again but found no faults using Mr Haynes' checks . I found a site giving checks with a multi meter and think that the low tension side of the coil is outside the given ohm parameters although it passes the bulb and battery test. I have now ordered a new coil to see if I am right. As an aside - I found lots of retailers offering 6v coils for CG125s but all were out of stock except one.So the freight restrictions because of Covid seem to be hitting us now.

 

Or they have a big problem with the coil and have all run out. :D :D

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1.

Has this bike ever ran in your possession ?

A lot of points based bikes have issues caused by incorrect rebuild procedure when changing contact breaker sets . Normally the insulating washer gets omitted or incorrectly installed causing the points to earth out inadvertently .


Check that this is not the case by inspection against manual diagram et.

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IMG_3708.thumb.JPG.4fe1c58f940e8b01e482584d56d29a5d.JPG

Looking at the wiring diagram when the ignition switch is off it stops spark by grounding the ignition system through a black/white wire. To rule out something funny going on in the ignition switch you could try disconnecting that black/white wire and make sure it doesn't touch anything and check if you've got spark. It's not likely to be the issue but if you can get access to that black/white wire it's an easy thing to rule out

 

That black and white wire is designed to ground though as it goes through a points set


Which if memory serves when closed earth out that system but not to fuse but to suppress the coils desire to set of large explosionsIMG_3708.thumb.JPG.4fe1c58f940e8b01e482584d56d29a5d.JPGb7be47dfc3c4f5ed5a8968a45ea3f7d8.thumb.jpg.e7fdc32092e423c7b4db1c3cd4ead9a7.jpg

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When the ignition switch is in the off position the black/white connects to green which grounds the positive side of the ignition system to prevent spark. When the ignition is in the on position the black/white and green are open so you get spark. I suggested he disconnect the black/white at the ignition to rule out a fault in the ignition switch.


disconnect the red circle

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I think in that setup the power for the ignition coil comes from the stator not the battery.

 

My apologies forgot the power enters from the stator directly onto the points and that just grounds the power and not from the ignition switch down to the coil etc .


Need to readdress my earlier post ...

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Hi. Thanks all for your suggestions. No I have not seen the bike running as it was found in a shed during a house clearance. Yes I have checked the ignition switch (new) and all is correct and belt and braces detached the b/w wire . I have checked the contact breaker set up and the lead is in the correct position with no leak through to the base plate. I have wiring diagrams which I do understand, as a retired design engineer. So this is why I have suspected the coil low tension side. Hopefully the new coil will sort it out, but if not, the only thing left is the generator output, detail of which i cannot find, only when running not when kicked over. As I said before, however, all checks for continuity on the coils are OK so not suspecting that at the moment.

In the back of my mind I think there was a way of linking the battery into the circuit to test for a spark , so eliminating the generator. I am dubious to try linking via the b/w wire in case I do some damage. Has anyone heard of this ?

Thanks again for listening to my woes

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If you disconnected the black/white where the red circle to isolate the ignition coil and condsender and briefly touched the positive of the battery to it you might get a spark at the spark plug or you might not. Or instead of that you could take the spark plug out so there's no compression and spin the engine over with a drill attached onto the flywheel nut. At your own risk of course :lol:

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I was reading through a link suggested by KiwiBob and had further thoughts - I checked the output to the B/W wire and could only get a very small reading ac or dc unlike the person in the link who was getting 6v on kickover. I looked at the stater properly and saw that someone had butchered the lower screws so I suspected previous problems. I had to drill them out to get the plate on my bench for a close look. Sure enough the black wire to the ignition side had come unwound so I guess was not giving full voltage although showing continuity. While I was looking round the pigtail wire departed from its connector, so obviously was only on with a couple of strands hidden by the sheathing.


So do I need a new stater or does the fact that the wire is still intact matter ? Help from an electronics wiz required please


-- or is the poor connection at the points restricting the output ? The plot thickens !


I am a bit fed up now, so will return to the problem this weekend because I will have to reassemble the whole thing to see if a good connection at the points cures it

.


If it is the stater - where to get one - I have searched and had no luck whatsoever ( 6v 2 coil set up ) Anyone got a suggestion.

I suppose I could bet a rewind, but how much would that be ?

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If you found a bad connection repair it and put it back together and see if that fixes it. I've not had a 6V bike or points and condenser bike but I'd imagine with only 6V to play with any bad connection could mean a weak or no spark. I've heard this company is good for electric parts. They should have any parts your need https://www.electrexworld.co.uk/index.html

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Hi WD-40 thanks. I will try again, but having to wait for the stater plate countersunk holding screws from David Silver. As I said, I had to drill the little %$&*$ers out!! I wonder what else I will find when I actually get it started ! Anyway I will let you know the outcome either way.

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Put it all back together - new points connection (soldered) checked connections, continuity in the stators, and re- ran tests for coil. The only thing left is that the generator is not putting out enough even though getting continuity. I get very low readings when I kick it over. Going to talk to some rewinding companies tomorrow and see what they think.

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