No spark at plugs

I am a new member who is trying to rehab a 1974 Commando that has been shed bound for about 25 years. Before investing too much time and money on mechanical repairs, I thought it might be worthwhile to see if I could get any spark to the cylinders first. No luck so far.
There is continuity in the brown/blue wire between the negative terminal on the new battery (12.7 v) and Pin 1 on the new ignition switch. (One of the contacts on Pin 1 on the old ignition switch had broken off. Took switch apart and tried to repair it but repair didn't work so I bought a new ignition switch.)
There is also continuity between the white wire on Pin 2 on the ignition switch and the white/purple wire on the negative terminal on the 6v coil, so it looks like power is getting to the coils when ignition switch is closed.
There is also continuity on the black/yellow and white/black wires between the positive terminals on the coils and the respective points.
Resistance across each coil is 2.0 ohms, which is a little outside the specified range of 1.7–1.9 ohms. Not sure if this discrepancy is a big issue or not?
Can't get any resistance reading across plug wires. Wires look good visually but plug caps are deteriorated. Will be buying new plugs and plug wires shortly.
When ignition switch is turned to Position 4, (ie. night-time running) , headlight and tail-light come on and red ignition warning light comes on.
I read an older post where a method of wiring directly from the battery to the ignition was described. I think it involved running a wire from the battery directly to the white wire on the Boyer ignition thereby bypassing the ignition switch, wiring harness, kill switch, etc. Is there a similar bypass that could be used when the ignition system is coil and points type? Would a wire directly from the battery to the negative terminal on the coils bringing power directly from the battery to the coils do the trick?
Any advice would be greatly appreciated.

Connecting the negative terminal of the battery to the terminal the white/blue wire is attached to on the ballast resistor will bypass the ignition switch and apply voltage directly to the coils through the ballast resistor. For general purposes remove the white/blue wire from the ballast resistor before connecting the battery voltage

Before you do that connect your ohm meter to the ballast resistor. It should read just a few ohms. Make sure you have good connections there.

Thanks, Arch. I'll give that a try.

Do you have spark/voltage at the points?

Glen

I checked the continuity of the wires to the points. I thought the points only acted as a switch that when opened caused the magnetic field in the coils to collapse sending a high voltage spike to the plugs. Not sure how to check for spark/voltage at the points. Can you describe how to go about doing that. Thanks.

When the points are closed, you should have voltage on both sides. when open, only one.

Checking an open set of points for voltage to ground is the best way. If you don't have a voltmeter, you should see a little spark when you open the points quickly. Alternatively touch a screwdriver blade or similar across the metal arms of the open points. You should see a light spark when the screwdriver blade contacts both.

No spark here then it won't run.

Glen

Make sure you have the points insulators positioned correctly. I had this issue, and no spark.

MikeM said:

Make sure you have the points insulators positioned correctly. I had this issue, and no spark.

Click to expand...

I was in your shoes in June. Replace condensers. Clean connections. And don't trust new spark plugs

If the points have been in the bike for eons, chances are they lack continuity when closed. Be sure to emery cloth them to clean them up and ensure they are conducting. I have had several cars that sat for too long and all that was needed to get them sparking was a point cleaning.

PJFlynn said:

I was in your shoes in June. Replace condensers. Clean connections. And don't trust new spark plugs

Click to expand...

The exteriors of the condensers are both corroded. The left one severely. Is there some way to test them?

Some multimeters have a capacitance function that can, IN THEORY, check a capacitor (condenser). BUT they do not actually test it with the load it sees in operation, therefore, it can test OK but not work under load. There are actual capacitor testers that can perform a proper check but unless you already own one, it's a bit pointless (NPI) to buy one to test caps on a Commando. BUT...

Keep in mind that the condenser is not necessary for the ignition to work; it is there simply to reduce arcing at the points. If you bypass the condenser with a piece of wire/alligator clips, then if the bike will start, you have proven the condenser to be the problem. If you do this, don't leave it bypassed and decide you don't need a condenser anymore because the points will burn/out/wear out very quickly.

Condensers are very cheap, best to replace if suspect.

Glen

Sometimes, if the motor has not been running for a long period, the carbon on the plugs seems to conduct and you get no spark. It is not common, but if it happens you can end up chasing faults where there are none. Fitting new plugs fixes the problem. It happened to me a while back after the bike had been standing for about a year. It didn't matter what I did, the motor stayed dead as a maggot until I changed the plugs. The problem might be more prevalent if you've been using fuel which contains alcohol.

Ran across this, I found it interesting re the quality of ignition capacitors nowadays - http://www.nonlintec.com/sprite/cap_failure/

At least with a rotating magnet magneto, the capacitor is usually where you can get at it. I don't know how many times I turned up at a race meeting with a reconditioned magneto, only to have it start missing after a few laps. Then I lost my entry fees, and travelling costs as well as the cost of fixing the unit..

I'm still trying to figure out why there is no spark at the plugs. During my investigation work, I noticed two things that I'm not sure about:
1. When the ignition key is turned to the on position, the red ignition warning light flashes once immediately when the key is turned on and then stays off, unless the points have been blocked open with a wood shim, then the red ignition warning light stays lit. Not sure what this means,
2. The other thing I noticed is that when the points are blocked open with the wood shim, I am getting a continuity reading across the open points. Again, not sure what this means. I thought that when the points were open there would not be continuity??

WEM said:

I'm still trying to figure out why there is no spark at the plugs. During my investigation work, I noticed two things that I'm not sure about:
1. When the ignition key is turned to the on position, the red ignition warning light flashes once immediately when the key is turned on and then stays off, unless the points have been blocked open with a wood shim, then the red ignition warning light stays lit.

Click to expand...

What about the other lights, horn?

WEM said:

2. The other thing I noticed is that when the points are blocked open with the wood shim, I am getting a continuity reading across the open points. Again, not sure what this means. I thought that when the points were open there would not be continuity??

Click to expand...

Assuming the points wires were still connected, then what you were seeing was continuity in the direction away from each contact, not between them, so try doing the test again but with the points wires disconnected.

WEM said:

I'm still trying to figure out why there is no spark at the plugs. During my investigation work, I noticed two things that I'm not sure about:
1. When the ignition key is turned to the on position, the red ignition warning light flashes once immediately when the key is turned on and then stays off, unless the points have been blocked open with a wood shim, then the red ignition warning light stays lit. Not sure what this means

Click to expand...

Yeah, that's not right. The assimilator should only be between the #2 position on the ignition switch and the AC side of the rectifier, and should have nothing to do with the points. You may need to regroup and try a temporary direct hot wire from the battery to the hot (not points) side of the ballast resistor, since it sounds like there's been some previous monkeying with the wiring harness.

WEM said:

2. The other thing I noticed is that when the points are blocked open with the wood shim, I am getting a continuity reading across the open points. Again, not sure what this means. I thought that when the points were open there would not be continuity??

Click to expand...

As MikeM noted earlier, make sure you have the points insulators stacked correctly. It's very easy to get the fiber washer in the wrong order, which then places the lead wire in direct contact with the points frame, which is grounded. Bad! Take a look at the following image for a good representation of the insulator's order of assembly:


With the two leads disconnected from the coils (black/white and black/yellow), the points should act as simple on/off switches, e.g. dead short to ground when closed, and infinite when open. If the leads are left connected to the coils during this test, you'll get some feedback through the coils shorting to ground through the opposite set of points. It won't be a dead short, but close to, as the coils have about 1.7 - 1.9 ohms each. Take a squint at http://classicbike.biz/Norton/Repair/NortonRepair.htm
for access to their online manuals and other cool stuff. You'll find the wiring schematics close to the bottom. Just make sure of the year series you're looking at

Nathan

Nater_Potater said:

As MikeM noted earlier, make sure you have the points insulators stacked correctly. It's very easy to get the fiber washer in the wrong order, which then places the lead wire in direct contact with the points frame, which is grounded. Bad! Take a look at the following image for a good representation of the insulator's order of assembly:

Click to expand...

That "distributor" diagram isn't correct for the Lucas points as it shows items in the wrong order and with the "wire from coil" and "breaker arm spring" in contact with the "attaching bolt" which neither must be.

Correct diagram, below, showing the ring terminal adjacent to the spring.



The common mistake is for the ring terminal to be fitted directly beneath the nut which grounds the wire.