No spark left side, right side fine - 73 850

Hello everyone!

I have a 1973 Norton Commando 850 that has a problem with getting spark on the left side. I cannot get ANY spark to come from that side.

Here is what I know:

Both coils are good (if I swap the wires from the right side coil to the left, the left fires, so it has to do with the wires coming to the coils)

Both plugs and plug leads are good (both work when I plug them in the right side)

Took the condensers off of my buddies running Norton to quick check if that made a difference, no difference, still no spark left side.

Checked the most right points (facing the bike on the right side, the lower right points connected to the black wire). There was some slight pitting but I cleaned them with 1000 grit and wiped and blew them clean, re-installed, still no spark.

I have a hunch that it has something to do with the points, but I am not completely sure.

What should I do? How do I test points, or how do I test the wires going to them?

I am VERY amateur with electrical related things, so if you recommend using a multimeter for any of your testing suggestions, please be as descriptive as possible for my sanity : ).

Next, my thought was swapping the points wires and if I get spark suddenly on the left and not right, then I would know it was problems with those wires or points.

Thank you so much for your time!

dlagrange said:

Both coils are good (if I swap the wires from the right side coil to the left, the left fires, so it has to do with the wires coming to the coils)

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Due to the Commando power unit shaking in the frame, it's not unknown for the copper strands to fracture unseen inside the insulation where the points wires enter the crankcase so you could try running a test wire from the LH points assembly to the coil and see if that cures the problem, if so, I suggest you renew both coil-points wires.

dlagrange said:

Checked the most right points (facing the bike on the right side, the lower right points connected to the black wire).

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The LH coil/points wire is normally black/yellow. RH is black/white.
The rearmost/LH points set as you look at them would normally be the left-hand coil/cylinder (black/yellow).

Did you confirm if left side coil is good? You could swap both coils left for right to check. If then right no fire, issue is bad coil. Can also use multi meter to test coil primary resistance (1.5-2 Ohm is normal range, open circuit is fail). Need to have all connections removed from coil for this test.

I am wondering if the wire at the left points is grounded... did this just happen - did you do any wire swaps at the points?
It could be the wire at the points is grounded, not on the right side of the plastic insulator; compare closely how wire is connected at the points between the left and right side sets of points. Or possibly the wire between the point set and coil is chaffed and the wire grounding on the frame.
Do you have 12V at each of the primary coil terminals?
With the points closed and ignition on, you can just manually open the points and the plug should fire.

YukoNorton said:

Or possibly the wire between the point set and coil is chaffed and the wire grounding on the frame.

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Okay time for a dirty little admission, the previous owner had soldered the black/white cable to the metal connector ring.

The was the very first next thing I was going to replace/ restrip the wire with a new connector.

I was not completely convinced this was the problem only because the solder is very solid with clear bunch of copper strands making direct and solid connection to the metal ring, so thought clearly the electricity would pass correctly.

However, reading your above sentence reminded me of some of the exposed copper wire that I believe is touching engine metal in the points housing.

Could this cause one coil not to fire?

dlagrange said:

However, reading your above sentence reminded me of some of the exposed copper wire that I believe is touching engine metal in the points housing.

Could this cause one coil not to fire?

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Possibly, but that should be the right-hand points set with the black/white wire.

L.A.B. said:

Possibly, but that should be the right-hand points set with the black/white wire.

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Hmmm. Okay, well I did not take apart the points connected to the black/yellow wire to check for corrosion or pitting.

I think my first two action items will be to clean the points connected to the black/yellow wire and crimp a new connector ring on the black/white wire.

L.A.B. said:

you could try running a test wire from the LH points assembly to the coil and see if that cures the problem

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Click to expand...

If I were to try this, I would run a wire directly from the points metal circle connector to a terminal on the left coil? I am assuming this wire should be connected to the positive (+) terminal on the coil and leave the negative terminal wire as is?

dlagrange said:

Hmmm. Okay, well I did not take apart the points connected to the black/yellow wire to check for corrosion or pitting.

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Check it is actually the black/yellow that's connected to the LH coil. The ring terminal looks as if it needs repositioning. The points faces also don't look parallel. The eccentric adjusters are also missing.

dlagrange said:

If I were to try this, I would run a wire directly from the points metal circle connector to a terminal on the left coil? I am assuming this wire should be connected to the positive (+) terminal on the coil and leave the negative terminal wire as is?

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Yes, the positive coil terminal. Keep the condenser wire connected.

Looking at your first picture, could the angled tab on the black/yellow wire ring terminal be touching the screw as that would short the points?

L.A.B. said:

Looking at your first picture, could the angled tab on the black/yellow wire ring terminal be touching the screw as that would short the points?

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I will check this.

As for the point faces not being parallel I was unaware that was important and had figured any contact, even two bottoms of the faces, would be all that is needed. Thanks for pointing that out.

That makes sense that the adjusters are missing! The manual said that those certain screws would adjust the gap as I tighten and loosened it, but when turning the screw it did nothing to move the points. I will look into replacing those. ATM I just put the feeler gauge in between the points at BTDC and tighten the screw that locks them in their place.

What is the easiest way to know what point is connected to which coil?

dlagrange said:

The manual said that those certain screws would adjust the gap as I tighten and loosened it, but when turning the screw it did nothing to move the points. I will look into replacing those.

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The two screws securing each set of points to the secondary backplate are loosened and the gap is set using a screwdriver blade in the 'V' notch. To set the ignition timing, either the pillar bolts are slackened so both sets of points will be adjusted equally by moving the backplate, or the secondary plate screws loosened so each set of points can be adjusted individually using the missing eccentric adjusters.

dlagrange said:

ATM I just put the feeler gauge in between the points at BTDC and tighten the screw that locks them in their place.

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Two screws secure each 10CA points assembly to the secondary plate (6CA has one).

Each points gap should be checked and adjusted with the points heel lined up with the scribed line on the points cam (Factory Manual, Section C40) so with the LH points heel close to the line as it is in your picture, the LH points should be practically fully open.

Also...
The eccentric adjusters aren't absolutely necessary, the ignition timing can be adjusted without them.

L.A.B. said:

Looking at your first picture, could the angled tab on the black/yellow wire ring terminal be touching the screw as that would short the points?

Click to expand...

My god that was it!!! Getting spark on both now. Thank you so much!