Topic: NO SPARK - COILS?

[GEARBOX]

Getting my 1978 CB750F running after a 25 year slumber.  New points, condensor, plugs, new fully charged battery, and for complete disclosure, I have been restoring the bike.  Took the headlight bucket off and disconnected a few wires, but they were clearly color coded and now back to where they should be. 

Now here is the issue, no spark on all 4.  The only thing I did not replace in the ignition were the coils (two) and associated plug wires and caps.

This is what I have done so far:

1)  Coil #1 - Blue wire reads 12V and Black/white striker wire reads 12V
2)  Coil #2 - Yellow wire reads 12V and Black/White striker reads 12V (the other one)
3)  Coil #1 - shows 1 ohm between the Blue and Black/white striker wire CORRECTION, READING TAKEN WITH COILS PLUGGED INTO THE HARNESS.  UNPLUGGED, READING IS NOW 5 OHMS.
4)  Coil #2 - shows 4.8 ohms between the yellow and black/white striker wire (the other one)
5)  Both coils were still connected to the harness when readings taken
6)  Kill switch (Black/White striker) shows 12V when in "Run" mode and slowly runs down to Zero Volts when in the "Off" position.

Obviously there is something wrong with the #1 Coil if I took the readings correctly, but to have no spark on all 4 cylinders strikes me as being a bit odd.  Both coils going at the same time?  Points are gapped at 0.014" and open and close, battery at full charge and still on the charger, power is going to the points as per the 12V readings on the blue and yellow wires, plugs gapped at 0.020", and the kill switch appears to be working.  It seems like the only thing left is the coils, wires and caps which I have already put an order in for, but again it is a bit strange. 

Is there anything else I should be checking and did I do the checks correctly?  Thanks Allan   

[PeWe]

Connect only one coil and check spark on plug outside the engine to SEE what happen or not. 
Coil 1/4 only (no 12V to 2/3 coil). Check spark. Then opposite with 2/3.
One coil might have a short that affect both.
- Check that the fiber washers are in correct place where the condensors are connected. 2 to each point.

If engine does not run due to wrong timing check rotor in adv unit.
Rotor wrongly mounted can be verified by switching yellow and blue cable from ignition to coils, engine will run then.

[TwoTired]

The coil voltage readings should be taken with the points blocked open.  In fact, when the points are closed the respective blue or yellow wires should have zero volts on them.  If not, your points have an insulating film over the contact area.

Burnish, NOT sand paper, the contact surfaces.  Then check across the point contacts for voltage when open and closed.  Should be near battery voltage when open and ZERO volts when closed.

[GEARBOX]

Two Tired - I think I am getting the opposite, when the points are open, the contacts are "not" touching each other on the points, voltage is zero, when they close, when the two contacts join together, I get 12 volts on the respective blue and yellow wires.  Did I mis understand something?

[GEARBOX]

PeWe -

I made a mistake.  When I tested the coils, they were still plugged into the harness.  So on the #1 coil where I got the 1 ohm reading, it is now 5 ohms unplugged.  I now see that when the points are closed, completing the circut and powering the coil wire, the coil will test out with the low ohm reading.  So now both coils are 4.8 to 5 ohms which tells me I have an extra set of coils coming.

I also took your suggestion and disconnected the two wires on one coil and then did the same with the other one.  Still no joy, no spark on any cylinders. 

Anything else I could be trying?  Thanks Allan

[GEARBOX]

This has gotten me truely stumped.  I've been working with points and distributors all my life and must be missing something really stupid here.  Coils test out ok at 5 ohms, new points and condesors and plugs all correctly set to factory specs.  Fresh fully charged battery and everything that should get voltage is.  Wires and caps?  Maybe, but all 4 at once?  Kill switch is providing 12V to both Black/White striker wires all the time, yellow and blue are energized until the points open turning off its 12V thus exciting the coils to provide a spark.  But no spark.  What am I missing here? 

[TwoTired]

Two Tired - I think I am getting the opposite, when the points are open, the contacts are "not" touching each other on the points, voltage is zero, when they close, when the two contacts join together, I get 12 volts on the respective blue and yellow wires.  Did I mis understand something?

One side of the points set connects directly to engine case, which should ultimately be connected to the battery NEG terminal.  Closed points must read zero V or zero ohms across them.

If you painted the frame/engine, check that the paint is removed where the NEG battery cable connects to engine case and frame.

[GEARBOX]

Two Tired - Yes, we are on the same page. sorry must of had a brain fart.  When the points are contacting each other the power grounds thus eliminating the power to the blue and yellow wires.  And yes, everything is grounded on the Bike, point plate, engine, frame, etc.  Have a few old English fiberglass cars and getting good ground is a never ending task.  Also the condensor and coil wires (blue and yellow) are well insulated by the fiber washers and not shorting to the ground plate.  Everything seems to be as they should be.

I think I drilled down the best I could and am hoping that both coils went bad.  Can a coil be bad and still show the correct ohms?  I have new coils and wires coming and see where that takes us.  But if you have any other suggestions, please let me know, Thanks Allan



 

[TwoTired]

Can a coil be bad and still show the correct ohms? 

I don't see how that is physically possible.

[GEARBOX]

Very weird, got the new coils today and she has spark.  Runs like crap, but its running.  Now to the next problem.