C 15 Help

[Alan1]

Looking for someone around Exeter to help with C15 no spark issue

[Spaceman]

The C15 electrics are relatively simple and, if you have a digital voltmeter, people on the Forum can guide you through the tests you need to do. To this end, it would be useful to know the history of the bike and whether this problem has just arisen or is this a bike that has not run for some time?

[Alan1]

Hi There
I bought it in boxes has not run in over 35 years
I have rebuilt the engine and put it all back together new wiring harness  points condenser coil battery new ignition switch etc
Set the points and timing as best I can but no spark

[Alan1]

Should have said new lead cap and plug as well

[Spaceman]

The ignition system on the C15 is incredibly simple to understand and test.  With the contact breaker points closed, the white wire to the coil -ve terminal provides 6V from the battery that generates a primary current of ~2A through the coil that exits via the black/wire from the coil +ve terminal through the closed points to ground (and back to the battery). When the points open, this primary current stops and, in so doing, the energy stored in the coil generates the high tension (voltage) spark.

Assuming everything is new, the first thing to check is that you are getting 6V at the coil -ve terminal via the white wire when the ignition is on. If not, there is a wiring fault to the ignition switch (unlikely).

The second thing to check with the ignition off is that the resistance between the coil +ve terminal (black/white wire) goes from open circuit (points open) to zero Ohms (points closed) as you rotate the engine. If this does not happen then, assuming the points are actually opening, the points may be assembled incorrectly and are inadvertently being shorted out.

If the coil is being powered up ok and the points are working correctly, then the problem must be with the coil or the HT lead, plug cap or spark plug. However, the problem is more likely to be with the contact breaker point assembly.

[Alan1]

Ok do if I put power to the coil I get a Spark . I don't seam to have power at the ignition switch .
Iam assuming the brown / white wire brings the power to the switch . It's a new switch  it has off ign on

[Spaceman]

Basically, the power comes in on the brown/white wire from the ammeter (if one fitted otherwise straight from battery) on to ignition switch terminal 2A. When you switch on the ignition, terminal 2A connects to terminal 3 which then carries power along the white wire to the coil. If you check the brown/white wire actually goes to the ammeter and should always be live irrespective of any of the switch settings.

[Alan1]

Thank you so much it was a bad earth to the frame now got a good spark

[SIMON.D.PORTER]

Hi Alan1
This is an example of the most common problem encountered in bike-car-vehicle electrical problems.
The first thing to check is whether the circuit has a good earth connection!
Cheers
Simon