No spark Honda CG125

[ThePhatomfart]

Know what your saying, the kickstart to spark on these are as basic as can be, dont need ignition , dont need battery, I've got the manual open in front of me and still cant figure why it will spark off the bike but not on it, is it haunted

[Jetskiover]

Its as though grounding the coil on the frame shorts the spark out !!!!

[ThePhatomfart]

Right as we know producing the spark with a battery works just fine , so we know that those parts work, producing the power for the spark through the kickstart is where everything falls flat and shorting is taking place, could the shorting be happening earlier in the process, is the Low Tension wire connected at the Breaker Points, trying anything here

[Jetskiover]

If I hold the black/white wire from the generator near the head and kick the bike over I get a strong spark. This is the wire which connects to the ignition coil. So 6v to the ignition coil is confirmed but nothing comes out of coil when fitted to frame and kicked over!!!!

[fastbob]

Its all well and good testing the coil with a battery but when you kick start the bike the current is coming from one of two generator windings ( the bottom one if memory serves ) the top one generates power to operate the lights and indicators and keep the battery charged . I can go and check all this in the manual ( and I may be wrong ) but having revived numerous CG,s bought as non runners , I can tell you that at least half of them wouldn't fire up until I had put a rewound generator coil in them .

[Jetskiover]

I have connected a multimeter to the black/white wire and get 6v ac coming out when kicked over. I think if i remember there is also a yellow and white which are as you say for charging and running the lights.

[Jetskiover]

Also the plug had a spark before I removed the head !!!

[fastbob]

Ok , you were posting while I was still writing . If you believe that the generator is producing enough current to make a spark to earth but not enough to supply the coil and capacitor then all you can do is test the generator output . But this is hardly possible if you can only do so momentarily when you kick over the bike . Have you tried temporarily re wiring the generator so that the top coil feeds the coil instead like I suggested ? Worked for me once or twice . What I'm saying is that just because you have some current it dosen't mean you have enough power .

[fastbob]

Ha ha , doing things faster than I can suggest them !

[Jetskiover]

Will try that and see what happens. There is a strong blue spark at cable though and analogue multimeter comes up to 6v.

[Jetskiover]

Thanks for all your help and happy new year too.

[fastbob]

I suppose you could hang the coil from the bike with tape , stick some petrol in it and start it . Then you could work backwards and see what makes it NOT run !

[Jetskiover]

Just been out to check voltage again. With a analogue multimeter and pushing over by hand I get around 5v from black/white wire which isn’t bad considering it is turning over slowly. But still no spark from coil at plug.

I think tomorrow I will try to add a earth wire from the base of generator to ignition coil without grounding it to frame and see what happens.

[ThePhatomfart]

Hi , while your down that end just make sure the LT wire is attached to the points and insulated

[fastbob]

Hi , while your down that end just make sure the LT wire is attached to the points and insulated

 

A good point , but of course this will entail pulling the rotor off its taper with a rotor puller ( Threaded type ) because Honda put the points inside the generator . Very easy to get the insulating washers in the wrong sequence but remember the OP didn't do anything except replace the TOP end .

[fastbob]

This might be useful as an alternative means of testing the generator coils .

[Jetskiover]

I Have replaced the points but have had a spark at the plug since doing that and this was before removing the head.

[ThePhatomfart]

Hi , while your down that end just make sure the LT wire is attached to the points and insulated

 

A good point , but of course this will entail pulling the rotor off its taper with a rotor puller ( Threaded type ) because Honda put the points inside the generator . Very easy to get the insulating washers in the wrong sequence but remember the OP didn't do anything except replace the TOP end .

 

Yes , I do know the setup for the points and how to get at them, like you I have been working on bikes for 50 years

[Jetskiover]

Had a bit more of a look tonight. So i can get the plug to spark on bike with ignition coil bolted in place using 6v battery and earthing the battery to the coil or head. i think it is a problem with earth connection between the engine and the frame where the coil bolts on.

[ThePhatomfart]

Yes , would run a thicker wire from engine bolt to a good position on the frame, maybe a 12 gauge wire should work, have a look here for wire and explanation, or even a braided earthing strap

https://www.12voltplanet.co.uk/cable-sizing-selection.html

or

https://www.ebay.co.uk/itm/Braided-Earth-Strap-Car-Engine-Gearbox-Battery-Choose-lengths-9-18-or-24/254215315023?var=553599109010&hash=item3b3069de4f:m:m2cjromliNfXhtpDxg_SPRw

[Jetskiover]

Thanks for the help. Am hoping I may be onto something and will let you know how i get on.

[TimR]

Had a bit more of a look tonight. So i can get the plug to spark on bike with ignition coil bolted in place using 6v battery and earthing the battery to the coil or head. i think it is a problem with earth connection between the engine and the frame where the coil bolts on.

 

As a temp fault finder tool ...use a jump lead ( booster cable) as a temp earth cable

[Jetskiover]

Sounds like a good idea.

[Jetskiover]

Still just as confused by problem!!!

Have put a earth wire from a screw on the backplate for the voltage generator to screw holding the ignition coil to bracket as a earth wire.

When i kick bike over and hold black/white wire connector to earth on the ignition coil bracket or the head I get a good strong blue spark.

If I use a 6v battery to generate a spark on the ignition coil when fitted correctly to frame and spark plug earthed to engine head I get a spark.

But join the black /white ignition wire to ignition coil and get nothing !!!!!

[fastbob]

This has gone on long enough . Please can we have some pictures of all the relevant bits . In the meantime I'll dig out my CG manual . Also , perhaps you could post a picture of a hand drawn schematic of exactly what is connected to what . Together we can crack this .