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Discussion Starter · #1 ·
Somebody please help me!!! I have a 81 cx500c that runs but wont drive. It idles great, acceleration and throttle response are good...but when I go to ride, it bogs down and dies and then doesnt want to start again unless I let it sit for awhile.
What I've done to it:
Rebuilt and gone thru the carbs (a few times); cleaned the tank, petcock, and ran new line to carbs; new coolant, oil change; new spark plugs; and I just installed the Ignitech Sparker DC-CDI-P2 hoping that would fix the problem. I performed the stator test (How to check or test the stator and pickups on a CDI Honda CX500 | MotoFaction and How to check and test the stator and pickups on a Honda CX500 - online test) and the results were this:
1-5
Correct

2-5
Correct

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
Correct

6-5
Correct

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

So...3/5, 7/5, and 9/5 are all faulty, but it says they wouldnt need replaced if using the Ignitech. i got the Ignitech and it still does the same thing. Now I am really starting to think it might be the size of my jets. bout to pop them open again and see what sizes are in them. It seems to me like the motor is getting flooded with too much gas and it dies.
I dont really know what else to do besides shop around for a good mechanic in my area. I just hate to do that when I feel confident enough to fix it. I just need to know the problem. Somebody please help!!
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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12,480 Posts
Failure under load could be caused by weak ignition coils. You might see spark, but it could be weak enough not to provide consistent fire. Faulty coils can also seem fine until getting warm. There used to be a resistance test for the coils, but I don't recall what values to look for. You might try testing them cold and warm and note any difference.
Common replacements are inexpensive "pit bike" coils. Something suitable for a CDI-fired 250 should work on each side.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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12,480 Posts
Welcome aboard, by the way! (Where are my manners?)
 

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Discussion Starter · #4 ·
Right on man. Thank you for the reception on the site. Currently I have just taken apart the bottom of the carbs inquiring on the size of the jets I am running. I am going to try cleaning the old jets real well and sticking them back in there. The new jets I put in them when I rebuilt them didnt have a stamp on them so Im not sure what size they are. The old ones look to be original to the carbs themselves. They have the Keihn stamp on them. The main jet is 78 and secondary is 115.
I will also check into the coil possibility as well.
 

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What are you running for air filter(s)? Try a brief run without the air filter.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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12,480 Posts
Right on man. Thank you for the reception on the site. Currently I have just taken apart the bottom of the carbs inquiring on the size of the jets I am running. I am going to try cleaning the old jets real well and sticking them back in there. The new jets I put in them when I rebuilt them didnt have a stamp on them so Im not sure what size they are. The old ones look to be original to the carbs themselves. They have the Keihn stamp on them. The main jet is 78 and secondary is 115.
I will also check into the coil possibility as well.
Ahh... I didn't realize you had replaced the jets.
The OEM brass parts (and float needles) will be much better than what you find in the kits. The 78 is the primary main jet. It should be screwed into aluminum. The 115 is the secondary main. It should be screwed into brass. If they're reversed, you'll get poor performance.
 

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Discussion Starter · #10 ·
So I finally am able to ride it without it dying. I put the original jets back in it. But now I cant get it to accelerate over 4K RPM's no matter what gear I am in. It also backfires alot now. on acceleration and deceleration. I tried running both with the pods and without. Ideas?
 

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You need to ultrasonic clean the carb bodies. You can not get the tiny , convoluted passages clean by poking a guitar string into the hole and spraying with carb cleaner. Do it properly , sort the carb issue then move on. I suspect you have esome electrical thing going on as well but one step at a time and eliminate issues as you go.
 

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Discussion Starter · #13 ·
Instead of cleaning the carbs again, what are the alternatives to replacing the original carbs with the same old carbs? I've heard or read somewhere that you can buy carbs for some of the pit bikes or atvs that will work. Does anyone know what carbs I can get that aren't crazy expensive for a 1980 cx500c?
 

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No carb swap will be plug and play: with the exception of Murray's Mikuni carbs which he sells pre-tuned for your particular bike. Probably crazy expensive.
Have you ruled out an ignition problem?
 
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