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1981 Honda CX500 Custom
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Discussion Starter · #1 ·
Hey all, first time poster, long time lurker. Im sure this has been addressed before but Ive been scouring the pages here and google and Im a little lost on where to go next.

I was given a 1981 CX500 C rat bike from a friend that was moving a few years ago. He said it was running okay until he dropped off of a trailer onto the right front of the bike. Smashed up the gauges, bent the front brake lever, tweaked the fender, broke the right side spark plug cap. whatever it's a free bike I'll take it and see what I can do. I was working on a moped build at the time so I put it covered up behind the chicken coop until a few months ago when I decided to see whats going on. Figured I would start with spark and see how it goes from there since I knew that was an issue.

Downloaded a wiring diagram and started looking around. Hooked her up to a 12v battery, with a few tweaks and a new starter solenoid (don't know if I actually needed the solenoid after cleaning the connections at the start button) she turns over when I press the button, GREAT the engine isn't seized up at least!
Alas though, still no spark.
All lights including headlight, brake light, and neutral light come on.
Replaced the coils with used (but supposedly working) coils that I got on eBay (not sure how to test these) and a used spark plug cap that came with the coils. Still no spark.
Jumped the clutch switch. Still no spark.
Checked continuity at the fuses. All good. Still no spark

I know that sometimes the CDI units can go in these things but looking at mine the CDI looks like its in great condition, no corrosion or anything, might be the cleanest part on the whole bike, but I know that doesn't mean much. Since he had it running not long before it sat I would like to keep diagnosing the problem before dropping the money on an aftermarket CDI unit (Ignitech or the like) so that I can know its a worthwhile investment.

Is there anything I am forgetting to check that could be vital to getting a spark? Are there any wikis or other sites that address a list of things to check when trying to get spark? Any info or links to get me on the right track would be greatly appreciated!

Thanks folks
 

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Hey all, first time poster, long time lurker. Im sure this has been addressed before but Ive been scouring the pages here and google and Im a little lost on where to go next.

I was given a 1981 CX500 C rat bike from a friend that was moving a few years ago. He said it was running okay until he dropped off of a trailer onto the right front of the bike. Smashed up the gauges, bent the front brake lever, tweaked the fender, broke the right side spark plug cap. whatever it's a free bike I'll take it and see what I can do. I was working on a moped build at the time so I put it covered up behind the chicken coop until a few months ago when I decided to see whats going on. Figured I would start with spark and see how it goes from there since I knew that was an issue.

Downloaded a wiring diagram and started looking around. Hooked her up to a 12v battery, with a few tweaks and a new starter solenoid (don't know if I actually needed the solenoid after cleaning the connections at the start button) she turns over when I press the button, GREAT the engine isn't seized up at least!
Alas though, still no spark.
All lights including headlight, brake light, and neutral light come on.
Replaced the coils with used (but supposedly working) coils that I got on eBay (not sure how to test these) and a used spark plug cap that came with the coils. Still no spark.
Jumped the clutch switch. Still no spark.
Checked continuity at the fuses. All good. Still no spark

I know that sometimes the CDI units can go in these things but looking at mine the CDI looks like its in great condition, no corrosion or anything, might be the cleanest part on the whole bike, but I know that doesn't mean much. Since he had it running not long before it sat I would like to keep diagnosing the problem before dropping the money on an aftermarket CDI unit (Ignitech or the like) so that I can know its a worthwhile investment.

Is there anything I am forgetting to check that could be vital to getting a spark? Are there any wikis or other sites that address a list of things to check when trying to get spark? Any info or links to get me on the right track would be greatly appreciated!

Thanks folks
unplug the kill switch. its a black w/ white tracer wire tucked under the seat near the cdi box. 'Ive had mine fail while i was riding into work. if yours was dropped and no longer has spark, id be suspect of the kill switch.
 

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1981 Honda CX500 Custom
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Discussion Starter · #4 ·

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1981 Honda CX500 Custom
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Discussion Starter · #5 ·
unplug the kill switch. its a black w/ white tracer wire tucked under the seat near the cdi box. 'Ive had mine fail while i was riding into work. if yours was dropped and no longer has spark, id be suspect of the kill switch.
Good to know that you had issues with it too. Once you said that it would make sense for it to be screwed up since thats the side that the bike was dropped on.
 

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'84 CX650E that is evolving into a GL500
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Before you do anything else, how are you checking for spark? Laying the plugs against the valve covers won't work because they are insulated from ground by their rubber seals (the heads of the screws that hold them on are grounded).

And if you still don't have spark with the plugs grounded it probably wouldn't hurt to make sure the caps have the proper 5000 ohm resistance and that they are connected to the wires solidly (the usual advice is to cut about a cm off the ends of the wires before screwing the caps into them).

BTW:
Welcome to the forum and welcome to the world of antique vehicle ownership (they own us, not the other way around). If you have been lurking for a while you have probably seen this before but now it's time for you to do it yourself:
Your bike is about 4 decades old and may or may not have had all of the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
 

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1981 Honda CX500 Custom
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Discussion Starter · #7 ·
Before you do anything else, how are you checking for spark? Laying the plugs against the valve covers won't work because they are insulated from ground by their rubber seals (the heads of the screws that hold them on are grounded).

And if you still don't have spark with the plugs grounded it probably wouldn't hurt to make sure the caps have the proper 5000 ohm resistance and that they are connected to the wires solidly (the usual advice is to cut about a cm off the ends of the wires before screwing the caps into them).

BTW:
Welcome to the forum and welcome to the world of antique vehicle ownership (they own us, not the other way around). If you have been lurking for a while you have probably seen this before but now it's time for you to do it yourself:
Your bike is about 4 decades old and may or may not have had all of the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid). And don't forget things like the rad hoses and the boot between the engine and swingarm (they can crack on the bottom where you don't see it).
Hey Bob thanks for the advice, definitely going to take my time going through this beast and make sure that she is truly safe and road ready before I fully trust her!

I was testing spark against the valve covers so good to know that they are insulated from ground. I tried it on another ground point and still no spark.
Pulled the Black w/ white wire from the CDI and still no spark. Pulling this stops the ignition switch from functioning too right? My ignition switch is pretty shotty.
Next step is going to be to check spark plug caps and wires. Then checking the CDI to make sure it's getting power.

Does anyone know a way to test if my ignition coils are any good? One of the coils I took off it was beat up but the other doesn't look terrible and the new ones I picked up were used so it would be nice to prove that they are functioning as intended.
 

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Hey Bob thanks for the advice, definitely going to take my time going through this beast and make sure that she is truly safe and road ready before I fully trust her!

I was testing spark against the valve covers so good to know that they are insulated from ground. I tried it on another ground point and still no spark.
Pulled the Black w/ white wire from the CDI and still no spark. Pulling this stops the ignition switch from functioning too right? My ignition switch is pretty shotty.
Next step is going to be to check spark plug caps and wires. Then checking the CDI to make sure it's getting power.

Does anyone know a way to test if my ignition coils are any good? One of the coils I took off it was beat up but the other doesn't look terrible and the new ones I picked up were used so it would be nice to prove that they are functioning as intended.
pulling the black w/ white wire shouldnt stop your ignition switch from working. all this wire does is ground the cdi module when you flip the kill switch, and i believe when you turn the key off.

the FSM should have the proper resistances for the coils.
 

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1981 Honda CX500 Custom
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Discussion Starter · #9 ·
Thanks for all the help here guys. Got to play with it a bit this weekend and still no spark but we've been able to prove that the majority of the electrical system is in good shape.

I did test the ignition coils and they seem to be good (i think) but when I tested the spark plug caps I noticed that they didn't show any resistance and there was no continuity through the cap. Im still somewhat of a newb with electrical systems. I think that this means my caps are bad but I am having trouble finding an exact answer. Can someone tell me if that is normal or a sign that the spark plug caps are bad?

Already looking at the non-resistor caps and resistor plugs off of wemoto but just want to make sure that I am correct before I pull the trigger.
 

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'84 CX650E that is evolving into a GL500
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To confirm, when you touch the leads together it reads zero ohms and when you touch the leads to the connector inside one end of the cap and the screw in the other end it reads the same as when the leads aren't touching anything?
If so, the next step is to take the insides out of the caps and make sure the resistors, springs &c are there and clean & functional and then see if there is conductivity through the caps without the parts installed (it is possible for them to fail internally).
 
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