Topic: No Spark at points

[brianbmw]

1978 CB550K, has no spark at the points or the brand new plugs.  Are there any obvious electrical checks i can do?  I can trace voltage with a volt meter but i'm not sure exactly where the power goes to the coils.  FYI all of the lights work.

Thanks,

Brian

[bollingball]

With ign sw. on power goes to kill sw. blk wire. then from the kill sw. it is a blk/white wire to the coils. So with both sw. on see if you have 12vdc at the coils. You did turn the kill sw on?? If you have power at the coils report back and we will talk about the points.

                                                      Ken

[OldSchool_IsCool]

+1 what BBall said.  With a good battery, key on, kill switch on, you should have +12vdc on the black/white wire at the coils.  From there, move down to your points.  hold open the points with the blue wire or stick a piece of paper between the points faces.  You should now have +12vdc on the blue wire at the points.  Remove the paper and slowly rotate the engine (may wana pull the plug wires to prevent accidental starting).  The volt meter should flip flop between +12v and 0v.

Repeat for the yellow wire.  Come back and tell us where things didn't go as outlined.

[brianbmw]

Thanks guys stay tuned hopefully i can report back tonight.

Brian

[brianbmw]

I just did a quick test.  The kill switch is working as it should and i have power getting to the coils through the black and white wires.  Is there away to tell if power is exiting the coils at the coils or should i move on to the points?

Thanks Brian

[Spanner 1]

Shine those point faces and the problem will 'prolly go away  .... no spark@ plugs, examine the point faces and shine 'em would be the first to do IMHO. The points can 'look' clean but have a slight 'film' on them which is often enough to stop them grounding when closed. Has the bike sat for a while with changing humidity/damp ? This is assuming the point wires ( Blue and Yellow ) are connected correctly at the points and not on the 'wrong ' side of the insulating washers ?

[brianbmw]

Did another quick check, I have 12 volts at the blue and yellow wires on the points when they are open.  I will try to shine them up a bit and report back.  Can i use a solvent on them or just fine sandpaper?

Thanks again guys, i'm narrowing it down now.

Brian

[brianbmw]

I cleaned the points and now have spark at the points and the plugs.  Thanks guys, now to work on the fuel.

Brian

[Kong]

So what you are trying not to tell us is that the first time you tried to check for voltage at the points that the points themselve were actually closed (and shorted out) when you tried to take the reading - is that correct?  Lesson learned.

Let me explain a little bit of what is happening here.  When power is applied to the coils a magnetic field is created within them.  That field does little to nothing as it just sits there, it does not create any spark just yet.  The blue or yellow wire that comes from the coil and goes to one of the sets of points has the purpose of shorting out that power that is going to the coils.  When the points close the power that was creating that magnetic filed goes directly to ground and the magnetic field collapses.  It is the collapse of that magnetic field that creates the surge of electricity that goes out what the secondary terminal of the coil - which is to say it goes out to the spark plug wire.  So while its actually the collapse of the magnetic field that creates the spark in what is called the "secondary wire"  its also true that you can not get that spark unless there is power into the coil through what is called the "primary circuit" and a line out of the coil to a switched (the points are nothing but switches) ground.  Oh, and just in case you were wondering; when the field collapses and the high voltage surge of power is directed down the secondary (plug) wire there is also a faint echo of that power surge that shoots down the blue and yellow wires to the points and causes a minute transfer of metal from the negative side to the positive side of the switch's contacts.  That is what causes your points to pit and wear out.

[brianbmw]

Thanks guys, it's running after sitting about 20 years.

[dave500]

sorry kong,,when the points close the coils are energised,its when they open that the spark occurs,youll have power to the black/white with them open or closed,the points are the switch that completes the circuit to earth.

[TwoTired]

sorry kong,,when the points close the coils are energised,its when they open that the spark occurs,youll have power to the black/white with them open or closed,the points are the switch that completes the circuit to earth.

+1

Points closed= energy stored in the coils, power drawn from the battery.
Points open = energy released from the coils = Spark

[Kong]

and now I understand why people have been calling me backwards-assed almost all of my life.

[OldSchool_IsCool]

Beautiful bike Brian!  Now ride the piss out of it!