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1978 honda cx500
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Discussion Starter · #1 ·
Hey there everyone, im new here and this is actually the first forum ive ever joined with these old bikes. Usually YouTube videos or reading other posts on these forums have been able to help me enough to get by, but im stumped right now so im reaching out. Im a bit of an amateur mechanic, so i should be able to attempy any repairs myself.

Ok so i have a 79 cx500 i bought at a great deal about a year ago, and it is my first big project to learn more about motorcycles. Its been an ongoing project whenever i have time off from work, the engine wasnt rebuilt at all, but i did flush everything thoroughly because it had been sitting for a few years prior. All new fluids have added, new parts have been wired and today was the day i got to finally take her out for a spin. Well, it was running beautifully at first, for about 20 minutes, the idle was at about 2k which was high but the idle screw on the carb didnt seem to be changing it at all.

After that 20 minute mark it began misfiring constantly and died. And anytime i attempted starting it, it would missfire and die, i couldnt get it to idle again. I come to find out the right cylinder isnt firing at all, i plugged the boots out one at a time and attempted starting the bike, and when the right boot was removed the bike instantly fired up and would idle, roughly but still stayed on with almost no choke. I switched the wires to the coils to see if the problem would switch to the other cylinder, and it did not. It wouldnt even start at all when the pink and yellow wires were switched.



So my main question, is this a sign of the stator failing? Or is the ignition coil itself bad? I have a coil/spark plug testor that goes in between the two, and i was getting a signal from it when i attemted to start the bike, so it seems like it should be working, but its not firing. Im just confused why im getting a signal from cylinder, but it wont fire. Ive already cleaned the carbs, and ensured both sides are getting fuel.

Thank you again for any help/advice you can provide, ive been wanting to get into bikes for some time now and feel like these antique bikes was biting off more than i can chew, but hey you live and you learn!
 

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If you have a multimeter run through these tests.
 

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1978 honda cx500
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Discussion Starter · #3 ·
If you have a multimeter run through these tests.

Ive done that test before, actually when i first got the bike and it passed. However i just did it again and ill copy and paste the results below, mainly because i dont fully understand them, and if they explain why only one cylinder is firing.

"First part of engine serial number:
CX500E
Second part of engine serial (Numbers only, required):
2017918
1-5
Your right pickup is faulty and needs to be replaced. This is required for both the stock CDI and Ignitech modules.


2-5
Your right pickup is faulty and needs to be replaced. This is required for both the stock CDI and Ignitech modules.


3-5
Your advance is faulty. Replace it if you’re running the stock CDI. If you are using an Ignitech the bike will run normally with a faulty advance.

4-5
Your left pickup is faulty and needs to be replaced. This is required for both the stock CDI and Ignitech modules.


6-5
Your left pickup is faulty and needs to be replaced. This is required for both the stock CDI and Ignitech modules.


7-5
Your advance is faulty. Replace it if you’re running the stock CDI. If you are using an Ignitech the bike will run normally with a faulty advance.

9-5
Some of the coils on your stator are faulty - if you are using the stock CDI you will need to replace the stator. The Ignitech does not require these coils to run.


9-8
Correct"

Thank you again!
 

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1978 honda cx500
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Discussion Starter · #5 ·
That doesn't tell us a lot. Give us your actual numbers.
Oh sorry! Here you go. Everything is in ohms except that one thats marked as kila-ohms. Also those were measured with the engine off, it said to read it with the engine on but i cant get the bike to stay on long enough to do that.

1/5- 122.1

2/5- 105.7

3/5- 247.8

4/5- 123.1

6/5- 103.4

7/5- 82 (kilaohms)

9/5- 346

9/8- 89.1
 

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I'll just dump this here where I can compare your figures.

209421


Quick question.

What figure does your meter give with the probes just touched together? This figure must be deducted from your readings.
 

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Discussion Starter · #7 ·
I'll just dump this here where I can compare your figures.

View attachment 209421

Quick question.

What figure does your meter give with the probes just touched together? This figure must be deducted from your readings.

It reads 0.2 ive already subtracted it from the values i sent. Wow it looks like all my values are off
 

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Discussion Starter · #9 ·
Was it a particularly hot day when you took the readings or the motor still warm from being run? Most don't look too far off.

I actually took them just now, the bikes in my garage its not hot in there, just very humid. What about that values that came in at 82 kila ohms? Is that a sign my stator is bad?
 

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OK.

The first thing is that you have no spark on the right. This would largely be dependent on the 1/5 on this test for starting and running up to @ 5000 RPM This number doesn't look too bad. It's a little high but so are most of your figures which could be meter error. I would actually expect this coil to be still doing its job.

2/5 a little high but should still be working IMHO.

3/5 - This likely is out of spec. As it's an advance coil it's not your immediate issue. Correctable with ignitech or raesan anyway.

4/5 - same as 1/5

6/5 - again a little high but should be working.

7/5 - definitely fubar. But as an advance coil not the immediate issue. See note for 3/5

8/5- OK

9/5 Out of spec but *I would suggest still able to start the bike.

I'm actually thinking a failed CDI unit.

While cranking check the power coming from the CDI left and right sides {pink and yellow wires.} I expect no output on the right.

Are you able to pull the terminals from the 8 pin block? If you swap 1 and 4 in the multi plug from the engine side and test again I expect the non firing side will remain on the right. If the issue is in the pickups it should move to the left.
 

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Discussion Starter · #11 ·
OK.

The first thing is that you have no spark on the right. This would largely be dependent on the 1/5 on this test for starting and running up to @ 5000 RPM This number doesn't look too bad. It's a little high but so are most of your figures which could be meter error. I would actually expect this coil to be still doing its job.

2/5 a little high but should still be working IMHO.

3/5 - This likely is out of spec. As it's an advance coil it's not your immediate issue. Correctable with ignitech or raesan anyway.

4/5 - same as 1/5

6/5 - again a little high but should be working.

7/5 - definitely fubar. But as an advance coil not the immediate issue. See note for 3/5

8/5- OK

9/5 Out of spec but *I would suggest still able to start the bike.

I'm actually thinking a failed CDI unit.

While cranking check the power coming from the CDI left and right sides {pink and yellow wires.} I expect no output on the right.

Are you able to pull the terminals from the 8 pin block? If you swap 1 and 4 in the multi plug from the engine side and test again I expect the non firing side will remain on the right. If the issue is in the pickups it should move to the left.

What should meter be set to when i read the pink and yellow wires? I had it on to read just the voltage which the battery read 12.83 but while cranking neither of those wires had a reading. Both were 0.


And i should be able to swap the pins, ill probably do it tomorrow after work and see what happens. If its just the cdi unit i hope thats gonna be a easy fix.
 

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To be honest I forget what meter setting to read CDI output as I've not had to do it for a while.

Just find one that reads on the good side and compare to the bad. Setting may be AC.
 

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Discussion Starter · #13 ·
To be honest I forget what meter setting to read CDI output as I've not had to do it for a while.

Just find one that reads on the good side and compare to the bad. Setting may be AC.

Ok so, i tried using my multimeter to get a reading on the yellow and pink wires, and on every setting it was 0, exept reading in ohms it was over limit on both of them.

I did however switch the 1 and 4 pins, and when i did that the bike wouldnt start at all, because the left cylinder wouldn't fire. But, if i switched the pink and yellow wires between the coils then the left cylinfer would fire, but the right one still doesnt fire at all. In fact the bike wont start unless i pull the ignition boot from the right cylinder.

Is this still signs of the cdi unit going bad? Is my coil bad? The thing is, if i switch the pink and yelloe cables, the right cylinder still won't fire even though i know for sure one of them works.


Thanks again for the info/help, im learning a lot!
 

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You're not looking for starting with the wires switched - merely for spark. The spark from the opposite side will be mistimed.

I have a CX with stock CDI in the shed. If I get the chance today I will take some measurements to find which multimeter setting you should be on for the test.
 

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Discussion Starter · #15 ·
You're not looking for starting with the wires switched - merely for spark. The spark from the opposite side will be mistimed.

I have a CX with stock CDI in the shed. If I get the chance today I will take some measurements to find which multimeter setting you should be on for the test.


Ahh i see, well im not sure if i mentioned it before, but i have a coil/spark plug tester that bridges the connection between the two and lights up. And ive been able to get a signal from the right, at least when its cranking, ill go test it again to see.

And i appreciate the help, i should have made sure it ran before doing all the work i already did on it.
 

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That's good as it can also show you the strength of the spark - not merely that there is one.

Sometimes a spark can be present but it's too feeble to ignite fuel under compression.
 

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Discussion Starter · #17 ·
That's good as it can also show you the strength of the spark - not merely that there is one.

Sometimes a spark can be present but it's too feeble to ignite fuel under compression.

Ok i just confirmed the light turns on for both cylinders. The one on the right MIGHT be slightly more dim but its such a cheap tool that its hard to tell the difference.

Assuming both are the same and getting a healthy spark, what else would cause the right side to not fire? I switched spark plugs and still no results.
 

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Do you have a link to the spark tester that you are using?

I use a spark stretcher but the tool you are using sounds like something else that I'm not familiar with.
 

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Discussion Starter · #19 ·
Do you have a link to the spark tester that you are using?

I use a spark stretcher but the tool you are using sounds like something else that I'm not familiar with.

Its a cheap tool i got from amazon for less than 10 bucks, it has a metal rod at one end, and a boot on the other. The boot goes over the spark plug and the metal rod goes into the coil boot.
 
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