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Discussion Starter #1 (Edited)
Symptoms:
bike will start, idle, and drive up to 40mph. however (in any gear) will not get past 4K rpm regardless of how much throttle is given.
also when i am up in the 3500-4000 rpm range the bike will sputter (i don't really know how to describe it) and "jump" faster. it results in a sudden aceleration for half a second every couple seconds. I don't know how it is supposed to sound, however it seems like it is being pretty loud about it.

I have been looking around the internet and it seems like a fairly common issue. but it also seems like every single person that has had this issue has a different solution.

What i have done:
I have run tests on both the stator and CDI and replaced the CDI box very recently. As far as i have been able to determine all the electronics are working reasonably well and should not be causing the issue. (with a small exception; the resistors in the spark plug caps were removed and replaced with metal rods leading to a very low resistance throught the spark cap, which i am planning on fixing).

I have checked the air filter and it looks like its almost new. however looks can be decieving and if someone knows an easy way to check the filter, i would be happy to check/clean it just in case.

I switched the wires (yellow to pink and pink to yellow) and the bike would not start, and i stopped trying when the (presumably) engine made a couple loud clunk/clanking noises.

Info on the Bike:
1980 honda cx500c
purchased this fall as a project bike.

the CDI had failed on the left side previous to me buying it, and the right side was going fast. meaning that the left side of the bike has not been running for a minimum of a couple months.

I believe that the bike was sitting for some time before I bought it. but am not sure what kind of time frame it was.
the battery is new and i was told that the fuel tank had been cleaned out.

My Plan:
I called a couple mechanics in the area, and first off they charge a lot more than i would like to spend, but based off what they said, I am planning to empty and clean out the gas tank, and pull off and clean out the carb.

a) I want to know what some other people think about the problem.
b) if anyone can point me toward a good guide for removal, cleaning, and puting the carborator back together corectly.
c) a guide for cleaning the gas tank and fuel system, and is that necisary.
 

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You have very likely got dirty jets in your carburetors. You need the main jets to be cleaner, and maybe the idle jets as well. You can either take everything apart and clean those jets, or you can buy replacements that are brand new and therefore clean, and just do the same labor but instead of cleaning the old jets, just replace them.
 

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Couple of questions.

Does this behaviour get worse as the bike warms up?
Is the sypmtom more pronounced in warm weather?
Does the bike run better over 6000 rpm? Try kicking down a gear or two to jack the engine speed up over 6 Krpm.

Have you checked the coil resistance on both the primary side and the secondary side when the coils are cold? When they are hot?

Frankly, I wouldn't take anything apart until I had better diagnosis of the issue.

I went thru a similar issue. The problem about drove me crazy. Then I sat down and began testing the ignition system. Started at the stator work to the CDI. All good. Went to the plug boots to work back to the CDI. Found the problem. Cost of repair was $35 USD.
 

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I would say it might be a coil issue as well. I had symptoms very similar to that and they only went away once I changed my coils. Check for any cracks and make sure they're grounded good. You can check the resistance of the coils too, there is a tutorial somewhere on here.
 

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Discussion Starter #8
I would say it might be a coil issue as well. I had symptoms very similar to that and they only went away once I changed my coils. Check for any cracks and make sure they're grounded good. You can check the resistance of the coils too, there is a tutorial somewhere on here.
Are you talking about the stator or the ignition coils?
 

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Ignition coils. They tend to cause trouble when they get warm or if it's humid out (assuming they are faulty) . My symptoms were that I couldn't get it over 4 k rpm without it wanting to die on me. It was like I hit a brick wall and it just didn't want to give. Switched them out for the pit bike coils and it helped a lot until my engine seized from a different issue. Now the new engine runs like a dream with the new coils.

This is the procedure to check the coils here: http://cx500forum.com/forum/technical-help-forum/12591-continuity-ignition-coil.html
 

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Discussion Starter #10
So I was riding it, and if I pull the choke out while I'm riding I get a bunch more power. I think that points a bit more toward the carb.

Could it possibly be something involving the exhaust pipes?
 

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Discussion Starter #11
I also checked the ignition coils and they look normal and the resistance was right on the 7.5k ohms. For both of them.
 

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Discussion Starter #12
Couple of questions.

Does this behaviour get worse as the bike warms up?
Is the symptom more pronounced in warm weather?
Does the bike run better over 6000 rpm? Try kicking down a gear or two to jack the engine speed up over 6 Krpm.
so starting it cold i get more like 3000-3500 rpm and after running for a minute or two it gets up to 4k.
i'm in portland so not much warm weather here especially right now.
I haven't been able to get it up any higher than 4k. i downshifted a but it gets me nowhere.
 

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James. You should have two readings for each coil for warm and cold conditions. Primary and secondary side. Hot and cold.

Try a simulated warm coil. Use a hair dryer to heat them up.
 

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Symptoms:
bike will start, idle, and drive up to 40mph. however (in any gear) will not get past 4K rpm regardless of how much throttle is given.
also when i am up in the 3500-4000 rpm range the bike will sputter (i don't really know how to describe it) and "jump" faster. it results in a sudden aceleration for half a second every couple seconds. I don't know how it is supposed to sound, however it seems like it is being pretty loud about it.
Last year I had suddenly the same symptoms.
The carbs were well cleaned in the ultrasonic bath.
BUT after ~20 kilometers the engine didn't run more than ~4.000 revs and with a lot of sputtering.
I removed one of the floating chambers and saw one of the jets laying on the bottom.
I screwed/fixed this jet again.
The bike run now good.
After ~10 km the same play as before.
Pulled the carbs, opened the floating chamber from the other side carb.
Again a jet was laying on the bottom.

The idiot was me. I screwed these two jets only by hand power. :grumpy:

Then I made it correct.

Now the engine runs faster then my guardian angel can fly.
 

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If pulling the choke changed the performance then it sounds like it is the carbs. Best bet is to pull them out and take a look, clean them again and then at least if that doesn't help you can check it off the list.
 

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wolfgang i suggest you increase the size of the high speed guardian angel by a minimum of 25 percent to allow

for the increase

always set your high speed angel to 20 percent higher than max speed to allow a safety envelope
 

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Discussion Starter #17
Symptoms:
bike will start, idle, and drive up to 40mph. however (in any gear) will not get past 4K rpm regardless of how much throttle is given.
also when i am up in the 3500-4000 rpm range the bike will sputter (i don't really know how to describe it) and "jump" faster. it results in a sudden aceleration for half a second every couple seconds. I don't know how it is supposed to sound, however it seems like it is being pretty loud about it.
Is there any chance that this problem could be caused by problems with the exhaust pipes. i was reading through the wiki and it was not very specific, however it seems like a problem with the tuning could cause the issues. basically that there is a blockage and the bike isn't able to get the kind of air movement for high rpms. it seems like it could also explain some of the reason for the spluttering/jumping. I haven't been able to find any threads discussing a problem of this type. if anyone can point me toward more information that would be great.
 
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