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Discussion Starter #1 (Edited)
My 1980 CX500D starts right up, idles and is running (relatively) good on surface streets through all gears and RPM's, but when I get it on the highway and am holding 70mph+ for more than a few minutes it will suddenly start bogging and sounding like one cylinder is coming in and out. If I pull over, let it idle for a few minutes and then start riding again the problem is gone until I'm back at mid-high RPMs in top gear again.

The bike had an Ignitech installed when I bought it.

I installed a G8 stator a couple months back which solved the issue of the bike dying after riding more than 20 mins.

The jetting is currently 90/125 for K&N pods and free-flow exhaust. *I have a set of Murray's Mikuni carbs on the way.

I'm wondering if it could be the coils and/or spark plug caps. Also I've read if the air dam is damaged it could be heating up the coils, and my air dam is missing a good chunk out of it on one side.
 

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wondering if your gas cap isn't venting properly anymore and starving the carbs for fuel
How about you go for a ride with a loose gas cap and see if that makes a difference
 

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Discussion Starter #3
wondering if your gas cap isn't venting properly anymore and starving the carbs for fuel
How about you go for a ride with a loose gas cap and see if that makes a difference
Thanks for the suggestion. I gave it a ride with the gas cap loose (a bit tricky with the deluxe tank and cover). I was still able to reproduce the issue but maybe not as bad? Either way, I think you're right that it does seem like its starving for fuel.

Hoping Murray's carb kit + new fuel filter will solve the issue.
 

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if it got even remotely better then to me I would be checking the petcock screen to see if its clogged
Then go and check the coils....visual inspection for cracks and then you can warm them up with a hair dryer and test them to simulate the hot performance conditions
 

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I just went through this problem. Would lose power about 65mph. But mine is GL and with a vacuum petcock. So I think it's different from yours.

After testing everything, and replacing the coils with VFR800 coils with new boots. Turned out to be my petcock diaphragm had fell apart inside. And it worked when I tested it the first time.

Changed to a manual petcock. Been a few hundred miles since... no issues.
 

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I have also had a similar problem with the vac. petcock setup...even an old loose vac tibe can make trouble. Switching to the manual type solved that.
But also make sure the spark plug cables- not the coils or caps, just the wires- are connected formly and in good shape...heat can cause an old wire with worn or dirty ends to start resisting more...you will have a spark, but it will be weak. This problem can seem exactly like a fuel/air mixture problem, symptom-wise.
 
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