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Discussion Starter · #1 ·
Hi everyone!

I've been making progress on my bike slowly but surely (1980 CX500). I still have a coolant leak, which I believe is from the radiator itself, but I have managed to get an exhaust together.

I noticed that my bike was running only on the LH cylinder and the RH is not firing.

The right spark plug has spark and is getting wet with fuel. I did a rough compression test by putting my hand over the cavity and it felt the same on both sides, but I'll be doing an actual compression test tomorrow to tell for sure.

What should my next step be? I was thinking maybe valve clearances or possibly timing? Thanks everyone for your help so far, this forum has been invaluable!

I attached a picture of the plugs. The one on the left is for the LH side and vice versa. I have a video of the bike running but I don't know if I can share it here or not.
 

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How does the strength of the spark compare to the side that runs?

Weak sparks can disappear under compression while being wet by fuel. A drop of fuel condensed on the tip will short the plug meaning no spark.
 

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Discussion Starter · #3 ·
How does the strength of the spark compare to the side that runs?

Weak sparks can disappear under compression while being wet by fuel. A drop of fuel condensed on the tip will short the plug meaning no spark.
I'd say it's very comparable. It's a very bright spark on both sides. I could try swapping the plugs to see if that changes anything.
 

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'84 CX650E that is evolving into a GL500
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It is often said that it should run if you have fuel, spark and compression but in reality they all have to happen in the right amount at the right time do do any useful amount of work.

Since the plug on the side that isn't running is wet I'd start with checking the ignition system but I'd also check for flooding, possibly caused by the float bowl overfilling and the overflow not allowing the excess to drain (a couple of things I saw on the forum today made me think of that).

It might not hurt to check the valve clearances either to make sure they were set with the engine at the correct points.

BTW: Don't forget to add your bike's model and year and your location to your profile (see Forum Settings link in my signature) like I asked you to last month.
 

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Discussion Starter · #9 ·
It is often said that it should run if you have fuel, spark and compression but in reality they all have to happen in the right amount at the right time do do any useful amount of work.

Since the plug on the side that isn't running is wet I'd start with checking the ignition system but I'd also check for flooding, possibly caused by the float bowl overfilling and the overflow not allowing the excess to drain (a couple of things I saw on the forum today made me think of that).

It might not hurt to check the valve clearances either to make sure they were set with the engine at the correct points.

BTW: Don't forget to add your bike's model and year and your location to your profile (see Forum Settings link in my signature) like I asked you to last month.
Thanks Bob, I just added all that, my apologies it took so long!
 

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Discussion Starter · #10 ·
Update for everyone:

Checked compression cold. Right cylinder (non-running) had more compression than the left (running cylinder). I forgot to take measurements WOT so I got 95psi for the right and 85 psi for the left.

Swapped spark plugs: No changes.

Swapped spark plug caps: Neither cylinder would run. It also sounded like the battery was struggling to turn over when I flipped them. I'm not a huge electronics guy so I wasn't sure what that was about.

Anything else I should check regarding the ignition system?

I'll make sure to look into the float bowl flooding as well. Is there a straight forward way of checking this?

I'll also do the CDI/Stator check soon as well!

Thanks all!
 

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When having difficulty that requires a lot of cranking with the starter it's good to keep a low amperage charger on the battery between tests and check voltage after charging, it should be around 12.8v fully charged.
 

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Also compression test with closed throttle is only good enough to show it has some. The accurate method is warm engine, open throttle. Of course in your case that can't be done until after the current issues are sorted out,,,
 

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Update for everyone:

Swapped spark plug caps: Neither cylinder would run. It also sounded like the battery was struggling to turn over when I flipped them. I'm not a huge electronics guy so I wasn't sure what that was about.
One of the plug caps is suspect. Measure the resistance of the plug caps.
I'll make sure to look into the float bowl flooding as well. Is there a straight forward way of checking this?
Replace the float bowl drain tube with clear hose and run the hoseup beside the carb. Open the bowl drain screw and observe the height of fuel inn the clear tube. It should be a couple of millimeters below the joint between the carb body and the float bowl.
 

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Discussion Starter · #15 ·
One of the plug caps is suspect. Measure the resistance of the plug caps.


Replace the float bowl drain tube with clear hose and run the hoseup beside the carb. Open the bowl drain screw and observe the height of fuel inn the clear tube. It should be a couple of millimeters below the joint between the carb body and the float bowl.
Should I measure the resistance of the plug caps from each other or just a ground?

The float test makes sense, thank you for your help.
 

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'84 CX650E that is evolving into a GL500
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Unscrew the cap from the wire and measure it end to end. They both should read 5000 ohms if they are in original condition with their resistors intact or zero ohms (the same as when you touch the test leads together) if the resistors have been removed.

Just a thought: When you switched the caps from side to side you did unscrew each of them from the wire it was on and screw it into the other wire didn't you? If you just moved the caps from side to side attached to their original wires (& coils) the left side would have spark when the right should and vise versa, which could explain why it struggled and didn't start.
 

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Discussion Starter · #17 ·
Unscrew the cap from the wire and measure it end to end. They both should read 5000 ohms if they are in original condition with their resistors intact or zero ohms (the same as when you touch the test leads together) if the resistors have been removed.

Just a thought: When you switched the caps from side to side you did unscrew each of them from the wire it was on and screw it into the other wire didn't you? If you just moved the caps from side to side attached to their original wires (& coils) the left side would have spark when the right should and vise versa, which could explain why it struggled and didn't start.
I see. I'm pretty sure I made a mistake, I didn't realize they could unscrew. I took the ignition modules off (under the gas tank) and switched each side. Let me try again!
 

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Discussion Starter · #18 ·
Unscrew the cap from the wire and measure it end to end. They both should read 5000 ohms if they are in original condition with their resistors intact or zero ohms (the same as when you touch the test leads together) if the resistors have been removed.

Just a thought: When you switched the caps from side to side you did unscrew each of them from the wire it was on and screw it into the other wire didn't you? If you just moved the caps from side to side attached to their original wires (& coils) the left side would have spark when the right should and vise versa, which could explain why it struggled and didn't start.
Hi Bob. The left cylinder cap was reading in the 5000 ohm area while the right side was all over the place, pretty sure it was in the mohm range.
 

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'84 CX650E that is evolving into a GL500
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It sounds like you may have found the problem. If you pull off the rubber boot on the end that goes onto the spark plug you should be able to put a suitable screwdriver in and unscrew the metal parts, allowing you to remove the resistor, spring &c for cleaning. I prefer to use electrical contact cleaner and a Scotchbrite pad to scrub off the corrosion on the removable bits and then cut off a corner of the Scotchbrite, shove it all the way into the cap , spray in some contact cleaner and work it around in the bottom of the hole with a small screwdriver (a paper clip bent into a small hook works well for removing the bit of Scotchbrite when you are done).

Wait a minute, did you say you had ignition modules under the tank? CX500s (with the exception of the CX500E and '82 only CX500C) came with Capacitor Discharge Ignition (CDI) with one CDI unit, usually mounted under the seat. The GL500, CX500E, '82 only CX500C and all CX/GL650 models came with Transistor Amplifier Ignition (TI or TAI) and have spark units (occasionally referred to as ignition units) mounted in various places depending on the model but I don't recall any model having them under the tank.
Do you maybe mean the ignition coils that the other ends of the spark plug wires are connected to?
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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I think he meant the coils, Bob.
The TI spark units aren't under the tank, unless someone moved them. If that's the case, the culprit in all of this would be PO wiring.
 
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