Ignition Breaking Down - 1985 Honda CB125RS

[Tedwood]

Hi, I did post a while ago about the problem I'm having. But have been unable to resolve.

The situation is: the bike starts first kick and idles OK, all electrics work fine. BUT, revving the bike on the centre stand it hesitates around 5000/6000 rpm but does still rev up to the red line at 11000 rpm.

However, on the road it will not go over 5000 rpm.

I suspect the ignition power is breaking down. The generator/alternator has 3 outputs:

1. Exciter Coil - powers ignition
2. Direct Lighting (side and headlights only)
3. Battery Charging (battery powers horn,indicators & brake lights only)

Strangely, if I disconnect both the Direct Lighting and Battery Charging outputs (has to be both) the bike runs perfectly with no hesitation on the stand and runs as it should on the road.

I really can't understand how reconnecting the Direct Lighting and Battery Charging outputs effects the ignition as all 3 circuits are separate and independent of each other.

As I'm really lost on this one and don't know how to carry out any further checks/tests. I think I will have to send the alt/gen windings away for testing/possible rewinding but I can't see how the windings can be the problem.

Any help really would be appreciated. Cheers.

[bikenut]

do you have access to a strobe timing light and does the ign "advgance".........some pics would help :karma:

the winding are insulated with a very thin layer of laquer or shellac which can and does break down due to heat and age etc......also the windings may/will be covered in an epoxy which again is affected by heat and age. if the epoxy is cracked, the crack can take out (break ) a wire resulting in a make and break contact due to heat. so the system may function correctly when cold and misbehave when hot, or vice versa.

does the cdi system have a pink wire (ign advance ) ?????
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nuts about bikes

[Tedwood]

Thanks bikenut.

I no longer have a strobe, broke bulb years ago, bike runs fine (with just the exciter coil connected) so I don't think it's the advance/retard mechanism (bob weights old type).

Yes, I think the problem probably is with the stator windings, being nearly 30 years old! Possibly, when current is flowing from the Direct Lighting and Battery Charging circuits (ie when connected to the loom) it is somehow interfering with the Exciter Ignition output at 5000 rpm. Incidentally, engine hot or cold makes no difference so it could be vibration that causes it when all wires are connected.

Bikes ignition is very old school, Contact Breaker Points!

Cheers