Spark, but no Start - 1979 CG125-K1 - SOLVED!

teedeeeff · L Plate Warrior Joined: 20 Mar 2015 Karma :

Hello All,

I'm looking for a bit of help before we send the old girl off to a garage.

I bought her maybe a month ago, with 12 months MOT, good condition for age.

After a battery charge (6v) and re-wiring (Just to be happy with all connections) she ran fine, new air filter to replace the old air box, carb is clear from what I can see, no issues and for the next 400-500 miles over 3 weeks I have been loving my first motorbike!

*THE PROBLEM*
After 40miles in the rain last Sunday, I arrived home for a pit stop between journeys and when I went to fire her back up. Indicators were dodgy. But, she fired up! She started no issue!

Few hours later making the trip home for the night, she wouldn't start. No love for me there. Nothing. Tried a push start. Quick fire up, throttle open, start, stop. A few seconds of life if that.

I slept in the office that night.

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I have tested the battery reading: 6.35v
Then charged it anyway.

After testing the flasher unit - It's knackerd.

Cleaned plug, Sparks on engine casing.
Then just to be sure I pulled the HT lead off and stuck my finger in it while a mate kicked her over - OUCH.

Carb looks clean, Main jet clear & clean.

No crap in tank.

Finger over plug hole, compression OK, more than enough to blow my finger off the casing.

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My thoughts are: If it's sparking, then it can't be the ignition coil or condenser. But perhaps the points are knackerd? The spark timing? I had the casing off this morning and the point's don't seem to move when the flywheel reaches it's F point.

Any info you need and i'll update this thread tonight.

Thank you very much, if you have any advice,

Thomas

Taught2BCauti... · World Chat Champion Joined: 12 Jan 2012 Karma :

You should be able to see the points moving open and closed as the cam passes, but if they are only opening a small amount, you will still get a spark, but too weak (because of reduced dwell angle) and too late (because the engine has to rotate further before the points start opening).

Try opening the points gap to about 15 thou when the cam is at it's maximum point of contact (about 10° before TDC) and try again.

If the points look a bit rough, try cleaning the contact surfaces with a small flat file, or replacing them for new.

Try rotating the engine a little, so that the points are fully closed, then open them manually with an insulated screwdriver and see if it makes a difference to the spark you get at the plug (with the plug resting on the engine casing).

If you get a spark at the points though, you will need a new condenser.
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Ariel Badger · Super Spammer Joined: 02 Dec 2006 Karma :

Put old air box back on.
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teedeeeff · L Plate Warrior Joined: 20 Mar 2015 Karma :

SOLVED IT!!!

So my new air filter... wasn't the problem.

Neither was the points.

Turned out that the Neutral Switch light wasn't working unless the bulb was put to the frame. Followed the trusty Haynes manual wiring diagram back to the Neutral switch under the left side engine casing and... Lo and behold the wire had slipped and was shorting out against the casing.

I have no idea how this stopped the engine starting. But it was.

Always believe in your Haynes manual!