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Discussion Starter #1
74 cb450 k7

Hi all, I've done my share of research on the forum and I can't seem to find the answer, most likely because it is a simple question and might be common knowledge.
We've got yellow, blue and black-white wires coming off the coils, and I gotta be honest, I have no smoking clue how to test these. I've managed to discover that the coil loops are about 4.5 ohms and 14k ohms, which I think means they should be good. Beyond that, I'm not sure how to troubleshoot, it stems from a lack of basic understanding about the ignition system. Could someone please give me a child-like explanation about the wires around the ignition system, including the key? And what should I be testing for in the black-white wires? And points? What are points?
I'm heading out to the garage right now to triple check that my connections are solid.
Thanks for your help!
 

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I'll try. The coils are nothing more than transformers that step up the voltage from 12 volts (battery voltage) to thousands of volts needed to jump across the spark plug gap. Like all electric circuits, there must be a complete circuit from the battery, through the wires, to the coil and back to the battery in order for them to work. The black and white wire provides the positive current to the coil and the blue or yellow provide a route for the current to return to the battery. The points act as an on/of switch for the circuit. If the points are closed, the circuit is closed and the points provide a path for the current to return to the battery. So, using a test light with the negative clip grounded (to the engine or neg terminal of the battery) touching the black and white wire, it should light with the key on, the kill switch on, AND the POINTS OPEN. If you close the points, the light should go out if they are properly grounded. <continued>
 

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In other words, current flows from the battery, through the ignition switch, the kill switch, the black and white wire, the coil, the yellow (or blue) wire, the points and ground back to the battery. During all this, the windings in the coil are creating an electromagnet field, and when the points open, the circuit is opened which stops the flow and causes the electromagnet field to collapse, which causes high voltage to discharge out through the high tension cable to the spark plug. I've probably confused you more, but ask questions and maybe someone else can help answer them.


(Before anyone chimes in, I'm aware that what I've said is not technically 100 per cent correct, but I was trying to describe it as simply as I could)


................Paul
 

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Discussion Starter #4
Actually, I can almost follow all that. Everything makes sense, more or less, up to the points. I get the concept of them interrupting the circuit, but I'll go do some more research about how they work and try that grounding test you mentioned.
If the timing was totally off, would that cause a no spark situation?
Thanks!
 

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If the circuit is operating correctly, you should have spark, no matter where the timing is. It may spark at the wrong time, but it should still spark.

.............Paul
 

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Discussion Starter #6
I just got back from checking my wiring. Everything seems to be in order and the lights that are hooked up are working. The engine cranks but I still don't see a spark when I touch the plug end to a good ground. I swapped out the coils for NOS coils and still nothing. I put the original coils back on.

I will check: the spark by removing the plug and touching the terminal with a screwdriver while cranking, ensure the kill switch is operating (not sure if a faulty kill switch would open the coil circuit or the starter motor circuit), Rub the point contacts with fine sandpaper, Check the condition of the spark advancer.
Advice is needed, otherwise stay tuned.
 

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I just got back from checking my wiring. Everything seems to be in order and the lights that are hooked up are working. The engine cranks but I still don't see a spark when I touch the plug end to a good ground. I swapped out the coils for NOS coils and still nothing. I put the original coils back on.

I will check: the spark by removing the plug and touching the terminal with a screwdriver while cranking, ensure the kill switch is operating (not sure if a faulty kill switch would open the coil circuit or the starter motor circuit), Rub the point contacts with fine sandpaper, Check the condition of the spark advancer.
Advice is needed, otherwise stay tuned.
Do you have power at the black and white wire? It's easier to check for spark if you connect a wire between the spark plug negative electrode and ground. The kill switch will open the ignition circuit, not the starter circuit. It's best to use a point file, not sand paper on the points, little grains of "sand" can foul the points surface. The spark advancer doesn't have anything to do with the engine getting spark, only when it sparks.

............Paul
 

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Discussion Starter #8 (Edited)
I ended up not touching the points, but I won't go in there with sandpaper, thanks for the tip!
I do have 12v at the black/white wire. The screwdriver method did not give any spark. The reason I checked the advance is because I found one on my workbench and panicked, luckily it's from a different motor. As for the kill switch: all 3 positions, off-run-off, showed no change. Shouldn't there's be some indication that the kill switch is doing something to the circuit? How can I test that the kill switch is working properly?

Edit: just found the schematic, I should be able to check the continuity in the switch wiring at different positions.
 

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Just butting in to mention that in a lot of those old points setups, if the person leaves the points set so as to send current (whatever you call it, lol) with the engine not running - so that the points are stationary instead of doing their regular off-on-off-on-off... - with the system energized (IOW, key on) for any real length of time, it could cause something to burn out (coil, IIRC).

From the above you can tell IDK what I'm talking about, lol. Since I don't, I almost didn't post; but this thread has been up for a couple of days and no one warned the OP not to leave things energized without ensuring that one of the points aren't closed (or whatever you call it) and I am guessing that if you're testing your coil (etc.), you might have the key on for more than a few moments with the engine not running, so...

(If someone knows what I'm talking about and can clarify for the OP, it'd be appreciated.)

Regards,
 

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Just butting in to mention that in a lot of those old points setups, if the person leaves the points set so as to send current (whatever you call it, lol) with the engine not running - so that the points are stationary instead of doing their regular off-on-off-on-off... - with the system energized (IOW, key on) for any real length of time, it could cause something to burn out (coil, IIRC).
Regards,

Sorry, I should have warned against leaving power on too long without the points opening as it can cause the coils to overheat, the points contact surfaces to pit, or the battery to discharge.


The kill switch is a basic on/off switch, you should be able to test it using an ohm meter. While cycling the switch, the circuit should open and close.


.............Paul
 

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Discussion Starter #11
No worries, I've only had the key on for a few moments while cranking and have observed a satisfactory wait time between running the starter.
I played around with the multimeter and poked at the contact breaker to try to learn its secrets. I tried a test I saw online with a test light, the light was supposed to go off at some point when I slowly rotated the engine, but after many slow turns, it never even flickered. I took a video of the continuity test. Are these things normal? (The test light staying on and the continuity in the video)

 

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Ok, so it looks like you've found your problem. From what I can make out, the white lead is attached to the spring and the contact points are open. There should be no continuity until the points close. It's hard to make out, but I think you've got a problem where the wires connect to the points. That wire must be insulated from everything except the spring. There should be insulating washers that keep it from touching and the wire must be positioned so that it's not twisted enough to touch ground. Somewhere I have an illustration that shows this more clearly than I've explained it. I'll see if I can find it.

............Paul
 

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Discussion Starter #14
I think I'm in big trouble.
Remember that other motor I mentioned? It too has a contact breaker, also cb450, so I wanted to swap them out. As I removed the housing, I didn't release the the cam follower spindle and it came out and I think the follower fell into the engine. Frustrated and defeated is how I'm feeling.
And thank you for the diagram, it really helped.
 

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Discussion Starter #15
Not as bad as I thought. I was able to remount the follower. The other contact breaker exhibited the same behavior. And since I tried swapping out the coils, that leaves us with the condenser. I'll check that tomorrow.
 

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Discussion Starter #16
I haven't tested the condenser yet, but I removed the coil and bypassed the contact breaker. I hooked up the positive lead to the positive terminal and grounded the spark plug with a jumper, then touched the yellow wire to the positive battery terminal and removed it as in the image below, emulating the contact breaker. No spark, but when I removed the spark plug and inserted a metal rod into the cap and held the rod very close to the engine block, I got the faintest tiniest little spark. Something it not right. Still searching.
image.jpg
 

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Discussion Starter #17
And if you read what I just wrote, you'll notice I screwed up the connection. Let's try again tomorrow.
 
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