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Discussion Starter · #1 ·
Hello all. I've been browsing on here since I purchased an 81 cx500 with 33,000 miles. The bike has been taken care of for the most part but has had an issue with the left cylinder(when sitting on the bike) misfiring when revving or accelerating. Here's a list of things I have done to figure this out. I have drained the gas, added new with seafoam, checked and cleaned the K&N air filter, cleaned the fuel filter, changed out the vacuum petcock, checked for any vacuum leaks, changed out and gapped new NGK spark plugs, checked over the carbs and found no blockages or varnish, and switched the coils to see if it was a weak spark issue. I also took apart and cleaned the plug caps. The machine idles smooth and runs good as long as you dont tach it up. The tach cable is currently broken so I'm not sure at what RPM it's starting to "break up" at. If anyone has heard of this problem, I'd really appreciate any advice. My heads starting to hurt from scratching it...lol THANKS!
 

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Hi Erik

As you dont say at what rpm its at, try swapping the igniter boxes to see if the problem switches from one side to the other ( the aluminium NEC units). they rarely fail, but start to go at higher revs, normally above 4500
 

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Discussion Starter · #3 ·
Hi Erik

As you dont say at what rpm its at, try swapping the igniter boxes to see if the problem switches from one side to the other ( the aluminium NEC units). they rarely fail, but start to go at higher revs, normally above 4500




Sounds like a good place to start. I'll give it a shot. Thanks!
 

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Discussion Starter · #5 ·
The carbs were gone over thoroughly and seem very clean. I noticed that the left header pipe doesnt get near as hot as the right. I'm thinking it may be an ignition issue. Could a failing CDI cause this since swapping coils doesnt also change the side the problem happens on? Also, the spark plug does seem dark, like it's not firing correctly but still getting fuel.
 

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Just for the heck of it, make sure the connections on the battery are tight. I had the same symptoms and it turned out to be a loose connection.



Also, don't these bikes have a main fuse(glass tube kind)? Check/ replace that. It could be cracked or loose. Even if it looks good change it anyway.
 

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If you have or can borrow an inductive (clamp-on) timing light, that can sometimes give you a visual confirmation of the misfiring high tension pulse. If it doesn't show up there, I'd look harder at carbs/air leaks/fuel supply.
 

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Discussion Starter · #8 ·
Thanks for all the tips. I checked all my connections, battery, connectors and fuses and they all have continuity. So the next step will be the timing light. I have an appointment to have my carbs syncronized with a local custom shop that owes me a favor, so that may help reveal a problem. Thanks again.....
 

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These pictures have been posted MANY times when there is a problem like this.



The low idle jet is under the rubber plug between the two jets. The hole is only .018" small. You mentioned that the carbs were varnished up and that you cleaned them out. But did you pull the low jet to clean it out like in the post link Harold gave you? One way you can do it without pulling the jet to do it properly is to soldier a .018 drill bit to a paper clip and use that to go down inside to clean it. It will give you fuel flow again to the low end fuel supply so it will run under throttle again. But it won't clean the entire jet. It also has an emulsion tube built into the jet that needs to be cleaned also. To do the job right it needs to be pulled out though.

When the low system is plugged you won't get fuel to that carb at the lower rpm's (idle to 5K)
 

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Discussion Starter · #10 ·
Well the problem seems to be gone. I swapped the coils out for universal ones that I purchased on ebay and it runs great. It's smoother than ever. I'm glad I checked over the carbs though, just for piece of mind. A new set of plugs with the new coils and a carb synch and she'll be at 100%!
 

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Glad to hear it's running better Eric. Sometimes working on one piece at a time to eliminate certain issues works out.

Keep it up on 2 and ride safe.
 

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Well the problem seems to be gone. I swapped the coils out for universal ones that I purchased on ebay and it runs great. It's smoother than ever. I'm glad I checked over the carbs though, just for piece of mind. A new set of plugs with the new coils and a carb synch and she'll be at 100%!
Hi Erik, can you give me part numbers/info on those coils? I have the same problem around 4500-5000 RPM on my '79 custom, even with clean carbs, new plugs, new fuel filter and air filter and cleaned-out gas tank.

--Bill
 

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Discussion Starter · #13 ·
Here is a link to these coils universal coils



Keep an eye out because it's possible to find the exact same thing for around $12 with free shipping from CA. I asked to have mine shipped priority mail (2-3 business days) and they did without charging extra.
 

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Here is a link to these coils universal coils



Keep an eye out because it's possible to find the exact same thing for around $12 with free shipping from CA. I asked to have mine shipped priority mail (2-3 business days) and they did without charging extra.
Thanks for the info, I'll let you know if new coils takes care of the problem. Once in a while the bike runs great, but lately not so often. Also, if anyone out there has a new Ignitek CDI I'm interested in buying one, rather than buying another 31-year-old unit from salvage.

-Bill
 
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