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1981 CX500 Custom
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Discussion Starter · #1 ·
So last fall during the PAC NW Rally with Nolimitz and DouginEasternWashington, my bike started behaving oddly.

It's had a full quad bypass, new Rae-san kit, new battery, new ignition coils, new spark plugs, new thermostat, and I had the carburetor done by the illustrious LRCXed
(Larry Cargill - he did SUCH an amazing job!). There's not a lot that I haven't replaced or serviced.

I noticed that when I would go to start my bike, it would be super tough to start, and once it did, it would act super boggy, almost like it was running on one cylinder - only I don't think it was. Barely any power, and it would at times die in the middle of a ride around my neighborhood. As I would continue to ride, it would suddenly and abruptly burst alive and lurch me forward at rpm with immediate power restored. Quite jarring. I then installed an in-line fuel filter, but it still happened up at the rally. We started one day on a chilly morning, and it was behaving like a turd for about the first 10 minutes of the ride, and I actually had to pull over on the side of the highway due to the engine dying. I got the bike started again....and then.....it was just fine. I was able to ride for over 100 miles problem-free.

I haven't yet pulled the petcock (mine is a vacuum petcock) but plan to do so, and I went ahead and bought a gravity petcock (and accompanying vacuum cap for the carb) to see if perhaps I have junk in there, but my tank is pretty danged clean.

I'm just now getting the bike back out from her long winter slumber. Any ideas or thought on how/where to start diagnosing and fixing this weirdness?

On a side note, I think I'd like to buy a couple of GY6 modules for testing purposes and to have on hand as a back-up just in case. They appear to be on Ebay, but I'm not sure which ones to spring for. Can anyone provide a link for some that would be good to purchase?

Thank you!
 

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I will add that when I saw the bike acting up I thought it was one cylinder cutting out. In my opinion the cut in and out were too abrupt to be fuel, but I have been wrong before. I am not a cdi expert or knowledgeable of the Rae-San ignition.
 

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it sounds like the gy6 - have you used the fault finding flow chart -
here

Cheers
Rayman
 
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1981 CX500 Custom
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Discussion Starter · #6 ·
So, this weekend, I'll be going through the whole wiring system and harness; I will also have the chance to test the GY6 modules. I'll report back with what I find. I'll also try disconnecting the kill switch as suggested. Thanks you all!
 

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Sorry about your troubles, its a bummer to do all that work and still having to chase down some gremlins. Hope its an easy fix for you.

Cheers
 
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Let us know how things pan out.
 
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'84 CX650E that is evolving into a GL500
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Re the petcock: A leaking vacuum hose or vacuum valve diaphragm can cause fuel delivery problems but they don't usually go away after you run it for a while.

But a failing pulse generator can start (or stop) working when it gets warm. Have you tested the pulse generators? It only takes a couple of minutes to unplug the connector and measure their resistances (this is covered in the FSM).

If those are OK try switching the spark units from side to side before you order new ones (throwing new parts at something is NOT they way to find out what is wrong). If the problem moves to the other side you have found the cause but if the same side still acts up it is something else.

BTW: The vacuum petcock is gravity fed too, it just has a vacuum operated valve in addition to the manual one.
 

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'84 CX650E that is evolving into a GL500
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I didn't notice that. In that case, swap the GY6 modules from side to side and see if the problem moves. Same as for the original spark units, if the problem stays where it was the problem is somewhere else.
 

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1978 CX500 "The Grub", '83 GL650, '82 GL500 Project "AdventureWing", '79 CX500C, '78 CX500 Scrambler
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I tend to agree with Doug,...
I tend to disagree with Doug. 😁
But here, I think he's correct. Your symptoms sound like a cylinder dropping out, to me. And the suddenness and temperature sensitivity point to electrical. It was either a failing G47, bad coils, or high resistance in the caps that caused it for me. That was a long time ago, and I don't recall what it was that resolved it.
Of course, your non-stock electrical eliminates some of this.
If the poor running is only at idle, or just off-idle, and the second cylinder kicks in as you accelerate (a fun facsimile of turbo lag), it could also be a restricted idle or primary main circuit in one carburetor.
 

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I tend to disagree with Doug. 😁
But here, I think he's correct. Your symptoms sound like a cylinder dropping out, to me. And the suddenness and temperature sensitivity point to electrical. It was either a failing G47, bad coils, or high resistance in the caps that caused it for me. That was a long time ago, and I don't recall what it was that resolved it.
Of course, your non-stock electrical eliminates some of this.
If the poor running is only at idle, or just off-idle, and the second cylinder kicks in as you accelerate (a fun facsimile of turbo lag), it could also be a restricted idle or primary main circuit in one carburetor.
On the the flip side, you’re only wrong when you disagree! 🧐😂
 

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I tend to disagree with Doug. 😁
But here, I think he's correct. Your symptoms sound like a cylinder dropping out, to me. And the suddenness and temperature sensitivity point to electrical. It was either a failing G47, bad coils, or high resistance in the caps that caused it for me. That was a long time ago, and I don't recall what it was that resolved it.
Of course, your non-stock electrical eliminates some of this.
If the poor running is only at idle, or just off-idle, and the second cylinder kicks in as you accelerate (a fun facsimile of turbo lag), it could also be a restricted idle or primary main circuit in one carburetor.
As a side note to this, Luke sent his carbs to Larry, he has new pit bike coils and I'm pretty sure he replaced the plug caps as well. His bike was in my garage for a couple months while we waited on every replacement part I can think of.
IIRC the poor running is at normal operating speeds while on road. sudden drop out only to recover moments after stopping?
 

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Discussion Starter · #17 ·
So, I just got done putting the bike back together thanks to the glorious Mobile AZN. I had found a "new old stock" wiring harness on Ebay that was in unbelievably good condition (new and supple and beautiful), and it was installed a short while ago. We went through the wiring connections and made sure everything was tight and sound. I was holding my breath when we turned the ignition key, but all the lights/indicators functioned perfectly and when I hit the start button, she came right to life after her winter slumber. She idled quite happily.

We let her warm up for about 15 minutes to get her blood and fluids circulating and up to temp. I rode her around the block and she seems to be working flawlessly. Throttle response was snappy and responsive (again, thanks to LCRXed). So far so good!

I'll be picking it up to drive it back home tomorrow, as the weather soured and became stormy.....but she seems to be back to her old self!

I'm wondering if I had some un-diagnosed wiring issue that was resolved when we put the new harness in. I'll report back after I take her on a more substantial ride.

I have new GY6 modules on the way thanks to Murray, and thanks to instruction by Mobile AZN, I now know how to properly crimp wires and attach bullet connectors. "The right tool for the right job."

I appreciate everyone's feedback and insights. I'll let you all know how it goes.

I love this community.
 
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