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Please help! No spark on cg125, I'm so stuck!!

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bevlak
Two Stroke Sniffer



Joined: 18 Jun 2018
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PostPosted: 09:07 - 15 Sep 2018    Post subject: Reply with quote

First of all thanks everyone for replying, very much appreciated!

So I'm going to post results as I test them.

Set to 200ohms on the multimeter and connect one to battery earth and the other to the black lead coming from the generator. With the points closed I get a reading of 0.4 and points open I get 2.4. does that sound right?

Thanks again
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Cg125 br-k '94
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jaffa90
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Joined: 06 Apr 2016
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PostPosted: 10:15 - 15 Sep 2018    Post subject: Reply with quote

That tells you that the points are earthing any signal to the ignition coil when closed as it should.
I don`t know the resistance reading when the points are open but have you a current going to the ignition coil when kicking engine over?
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bevlak
Two Stroke Sniffer



Joined: 18 Jun 2018
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PostPosted: 10:31 - 15 Sep 2018    Post subject: Reply with quote

jaffa90 wrote:
That tells you that the points are earthing any signal to the ignition coil when closed as it should.
I don`t know the resistance reading when the points are open but have you a current going to the ignition coil when kicking engine over?


Hi Jaffa,

How would I check for current to ignition coil? If you mean am I getting a spark the answer is no. I am getting slightly weird readings off the timing test you sent though. With the flywheel back on and slowly turning the engine I get a small spike at the f mark and a big spike at the t mark (90-160ish) but this just flashes up on the multimeter too fast to read properly and is not steady. Does that sound right?
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jaffa90
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PostPosted: 10:54 - 15 Sep 2018    Post subject: Reply with quote

It is a spike/pulse to the coil when the points just start to open, this 6v or 12v feed to the ignition coil low tension turns out thousands of volts at the high tension to the spark plug.
At the F mark the points should start to open and the piston just short of the top stroke.
I`ll try and find easier info in google.
This may help.
https://www.dansmc.com/magneto1.htm
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jaffa90
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Joined: 06 Apr 2016
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PostPosted: 11:03 - 15 Sep 2018    Post subject: Reply with quote

Also did you check the spark plug cap ?
I bought a lawnmower without a spark only to find that somebody had tried to open up the stator coil and failed.
The problem was the cap was not letting any current through due to a badly corroded suppressor inside.
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bevlak
Two Stroke Sniffer



Joined: 18 Jun 2018
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PostPosted: 11:03 - 15 Sep 2018    Post subject: Reply with quote

jaffa90 wrote:
It is a spike/pulse to the coil when the points just start to open, this 6v or 12v feed to the ignition coil low tension turns out thousands of volts at the high tension to the spark plug.
At the F mark the points should start to open and the piston just short of the top stroke.
I`ll try and find easier info in google.


Ok so I'm getting somewhere I think, the plug is now giving me a shock so that's progress I guess, but I still can't see a visible spark or actually start the bike. Any ideas how I can get that spark bigger??
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bevlak
Two Stroke Sniffer



Joined: 18 Jun 2018
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PostPosted: 11:04 - 15 Sep 2018    Post subject: Reply with quote

jaffa90 wrote:
Also did you check the spark plug cap ?
I bought a lawnmower without a spark only to find that somebody had tried to open up the stator coil and failed.
The problem was the cap was not letting any current through due to a badly corroded suppressor inside.


Yep this was replaced and tested ~10k ohms resistance to think it's ok!
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bevlak
Two Stroke Sniffer



Joined: 18 Jun 2018
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PostPosted: 10:00 - 22 Sep 2018    Post subject: Reply with quote

bevlak wrote:
jaffa90 wrote:
It is a spike/pulse to the coil when the points just start to open, this 6v or 12v feed to the ignition coil low tension turns out thousands of volts at the high tension to the spark plug.
At the F mark the points should start to open and the piston just short of the top stroke.
I`ll try and find easier info in google.


Ok so I'm getting somewhere I think, the plug is now giving me a shock so that's progress I guess, but I still can't see a visible spark or actually start the bike. Any ideas how I can get that spark bigger??


So after much testing and fiddling I have a nice fat blue spark!!!! 📣✊👌

Thanks everyone who helped here!! It was a combination of bad ignition timing, a duff spark plug cap and a corroded bullet connection leading into the ignition coil. Still not sure exactly which one was causing the problem but I think something must've damaged the plug cap when I moved the bike and the ignition timing just needed more fiddling I guess. All good now though!!

Thanks again everyone, much appreciated 👌
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