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Discussion Starter · #1 ·
Ok, Please give me some input here. I have an issue, I cant come up with a reason this is happening.



The bike runs awesome, I can fire it up and ride back roads all day long with no issue, hot or cold. When i get it on the highway it runs great, 70 to 80 is around 7k. After a while on the highway, say 10 min or so the bike won't run well under 6k anymore. Seems like one cylinder has cut out, runs rough as hell, try to accelerate and it will slowly accelerate with the occasional jolt of power (I am assuming as the other cylinder tries to fire). As soon as it hits 6k it's like a switch is flipped, runs great.. Till you slow or shift.



This only happens after a long run at 70 or 80, I hopped on the highway for 2 exits last night and it did it for a mile or so when i got off then ran well. When i stop the bike for a couple hours it is back to running well.



This is a strange one, anyone have an explanation? Carbs have been rebuilt, plugs are new, just set the valve clearances, compression is good in both cylinders, tried without the gas cap to make sure ts not vapor lock.





Any ideas? Please post some logic or a reason if you have a solution? i am as interested in what is happening as i am with fixing it.



Thanks a lot in advance,

6
 

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if you are sure the carbs are good,id have a stab at the coil breaking down,or HT leads,both cheap to replace
 

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Discussion Starter · #3 ·
I am reasonably sure the carbs are good. THey have been rebuilt, not synced. Unless its flooding one cylinder while cruzing at that speed i can't see sync being the issue.



What should the float heights be?



I will pull a plug lead next time it acts up and see if there is spark on both.
 

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Another example of the importance of listing your bike's model in the signature block. We have no idea if we are dealing with a CDI, or TI model. EVERYONE who has not done this, go back to your profile page and list your model in the signature box and while you are there, put your location in too.



Float height should be 15.5mm, from carb flange to bottom of the float when carb is tilted to the float tab just touching, but not depressing the float needle spring.



It sure sounds like a electrical breakdown somewhere. Plug caps, bad resistors, coils, HT wires, cracked boots on plugs, CDI (if you have one) or stator.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Mine wasn't exclusive to the highway, but when I had this problem a couple years back, it ended up being a bad coil. Get a decent used pair on eBay, and swap them out one at a time to find the bad one.



I know what you mean about "like a switch is flipped." It almost felt like I had a Turbo that would go to boost at 5500.



R
 

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I am reasonably sure the carbs are good. THey have been rebuilt, not synced. Unless its flooding one cylinder while cruzing at that speed i can't see sync being the issue.



What should the float heights be?



I will pull a plug lead next time it acts up and see if there is spark on both.


You really should check the sync after a rebuild of the carbs. Good balance will make for a happier engine down the road. I think ditto to those above about your coils.
 

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I am reasonably sure the carbs are good. THey have been rebuilt, not synced. Unless its flooding one cylinder while cruzing at that speed i can't see sync being the issue.



What should the float heights be?



I will pull a plug lead next time it acts up and see if there is spark on both.




See this thread,



http://cx500forum.com/index.php?/to..._p__4679__hl__airdam__fromsearch__1#entry4679



If your bike is supposed to have an Airdam it and it's missing it could be the cause as this sounds like overheating coils.They may have now been damaged by heat so,



http://globalcxglvtwins.hostingdelivered.com/viewtopic.php?f=10&t=335
 

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Hmmm thats a strange one

No real ideas as yet just trying to sum up the conditions

Extended running at 70-80mph so motor must be getting well warmed up

70's about 6 thou, 80's about 7 thou

high fuel flow in that condition

more power going through the igntion system

symptoms dont occur at slower cruising

and go after a cool down

Wheres me tarot cards?



Guesses:

as well as checking the the above.



Is the air inlet on top of the air filter facing backwards?

the cx doesnt like to be 'force fed' air and any hot gusts may upset it

and I was advised way back to not have it facing forward



the kill switch contacts must be either very high (run) or very low (stop)

anything in between is suspect and may rob power from the ignition

this is just a vague theory mind you, but lets say theres build up of crud

with partial ground leakage that worsen as it gets heated

Higher engine rotation may allow some wastage yet be less forgiving at lower revs



No, I dont like it much either, but its just a wild guess.



CDI components heating and leaking in a similar way to the above?



Ditto checking the plug caps, those original ones can be well burnt out nowadays.

they may heat and expand to the point where only higher revs/voltage can

punch through.
 

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Electric Components can develop what is called an "intermittant" either shorting, or opening or sending incorrect voltages. This is the voodoo hoodoo stuff that's hard to diagnose due to inconsitency (as in, it will never screw up in front of a mechanic) the following is Something I gleaned off the interweb which sums the issue up nicely.





Intermittants seem to fall under 2 broad categories:



1-"Mechanical Intermittants (a problem which appears from motion).

2-Thermal Intermittants (Problems which appear or disappear with a change in ambient temperature).



For mechanical intermittants, the Wiggle Test is the most effective. Wiggle every wire related to the suspect circuit, push and pull on each wire in each connector, tap suspect assemblies firmly with a screwdriver handle, flex every inch of a wiring harness, and examine the internals of each plug-jack connector.

***The components which are most likely to fail are those which are subject to the most vibration, and those which are subject to the harshest environment, which leads to corrosion. For example, battery terminals need to be cleaned periodically, because they are subject to a light sulfuric acid vapor atmosphere. Braided ground straps almost always fail from these factors.



Thermal intermittants are slightly more predictable. A failure occurs as the temperature rises or falls. Electronic techs have 2 tools for troubleshooting thermals. The first (laugh if you want to) is an ordinary hand-held hair dryer. Use it to add heat to a suspected component, and watch for a premature change failure.

The second tool is Freeze Spray. This is a spray can that contains a combination of chemicals which have an extremely high evaporation rate, thus dramatically cooling whatever it hits. Freeze spray is available at Radio Shack, and from most electronic supply stores. This is THE thing for troubleshooting, say, a motorcycle which quits after a few minutes of driving."





***I suggest using truck lite dielectric compund and refurbing all the block and plug connections.... then go for the more involved process of isolating the issue.
 

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Try plugs first, you can get a dud, straight out of the box. Make sure gap is wide enough.



Could also be a stator issue, They have CDI generator coils. One operates above 5,500 and one below 5,500 (approx) The stator issue only shows it's ugly head when the engine is hot.



Thats assuming you have an early CX.
 

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I am reasonably sure the carbs are good. THey have been rebuilt, not synced. Unless its flooding one cylinder while cruzing at that speed i can't see sync being the issue.



What should the float heights be?



I will pull a plug lead next time it acts up and see if there is spark on both.


How were the carb rebuilt? With an ultrasonic cleaner???



More often than you think a carb rebuilt will cause it to run worse if it only loosens up the crud without removing it.



I suggest that you buy Larry's carb book and follow it verbatim. It really does make a difference how you clean the carbs. If you use carb cleaner without proper disassembly you can do more damage than good.
 
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