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Discussion Starter · #1 ·
Looking for some advice regarding my 1982 GL500 which starts and idles fine until it warms up. Once it's warmed up it idles fine for a minute or less and then it speeds up to 2-3000 RPM or so for a few seconds then slowly goes back down to idle (cycles this way). The bike did this when I purchsed it so I cleaned the carbs using an ultrasonic cleaner and Larry's carb book. Carbs were clean for a 28 year bike; the only thing I found during cleaning is one of air cutoff valve diaphrams was split.I replaced all the rubber parts. Carbs also seemed to be all original. Idle mixture screws are set at about 1 5/8 turns which is what Honda recommends in the service manual. Larry's book says to start the idle mixture screws at 2 1/2 turns - could that be my problem? The screws have the cap on them preventing me from turning them more than 7/8 of a turn (unless I take the float bowl off).Carbs are syncronized at idle then when I rev the engine the Carbmate syncronizer LED's go to the red on the right cylinder. I have checked the valve clearances and they are spot on.

My suspicion is that it's carb related and it's most probably my right carb which still has some clogged passages.

What should be my steps to diagnose and fix this issue?

Thanks in advance.



Roland
 

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Check for air leaks between the carbs and the engine. I use an unlit propane torch and move it all around the intakes and connections between the heads and where the carbs connect to the rubber intakes. You could also have air leaks around the throttle shafts on the carbs themselves or the boots between the carbs and the airbox.



If there is a leak somewhere you should notice a difference in the idle speed when the torch is placed near it.
 

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Discussion Starter · #4 ·
Thanks Allen & Shep.

I will try the intake test and relook at the float setting & check float needles. During the bike rebuild I inspected the intakes and replaced the o-ring in between intake and cylinders. Both float needles and seats looked good during the carb cleaning. I have noticed faint smell of gas near the bike but no visible damp spots of fuel anywhere (assumed it was normal for an old bike) - it could very well be float/float valve issue.
 

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Be sure to check your plug BOOTS for cracks or chips ....and even the wires. 2 1/2 years ago I pulled my carbs I don't know how many times....was acting like yours and the problem ended up being a crack in the plug boot. Replaced that boot and here we are 2 1/2 yrs later and she still runs good.



Bad spark can cause the issue too.
 

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Discussion Starter · #6 ·
Looks like Rickbert hit the nail on the head.

I used a spark tester on both plug wires - sure enough the suspect right cylinder boot was arcing all over the place. After close inspection I noticed multiple cracks in the boot and etching from all the arcing. All the frustrations thinking it was carb related were probably unwarrented - I think. I'm glad I didn't take apart my carbs again! I ordered the NGK straight boots SB05F on bikebandit and purchased plug wire at my local shop. I'm very confident that was the bulk of my problem (if not all). This issue is probably why the bike was for sale.....the guy couldn't fiqure out what was causing it.

Thank you rickbert.
 

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Discussion Starter · #7 ·
Buy the way looks like the original 90 deg plug boots are still available - $30 each on bikebandit. Too rich for my blood right now but may get them in the near future.
 

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Looks like Rickbert hit the nail on the head.

I used a spark tester on both plug wires - sure enough the suspect right cylinder boot was arcing all over the place. After close inspection I noticed multiple cracks in the boot and etching from all the arcing. All the frustrations thinking it was carb related were probably unwarrented - I think. I'm glad I didn't take apart my carbs again! I ordered the NGK straight boots SB05F on bikebandit and purchased plug wire at my local shop. I'm very confident that was the bulk of my problem (if not all). This issue is probably why the bike was for sale.....the guy couldn't fiqure out what was causing it.

Thank you rickbert.


DO let us know how it turns out when you get your new boots and wires installed !! I'd love to be right !




I bet if you take one of your boots to an auto parts store and just started looking at other "auto" boots that you can find one that is the same width and the same length if not longer (which would work)that would fit into the hole and onto the plug. No it won't look "stock" or totally cover over the plug hole like the stock ones but they just might work until you can afford the stock ones.....just don't wash the bike or ride in the rain until you get the correct ones that will totally cover the plug hole !



Obviously you'd cut the other end off and the wire down to size and hook it into your coils at the other end.



Obviously IF you do this look at the ones for 4 cylinder cars....this way you're only wasting your money on 2 extras.



Let us know !
 

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I wonder if you were to wrap the plug boot in electric tape if that would be a temporary fix.



I would think if the arcing was the problem the idle speed would slow down when the arcing occurred and come back to normal when the plug started to fire again.



Also, just a note for anyone reading this with a pre 1982 CX, you cannot easily change plug wires as Rick describes above,,that option is for GL's and 1982 and later CX's only. You can change the boots though.
 

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Discussion Starter · #10 ·
Rickbert

Just to let you know - I replaced my plug wires and boots and the bike now runs great.

The right cylinder plug boot was the problem. Been a few shakedown rides to take the kinks out. I had done a partial restoration over the winter after I purchsed the bike last Dec. This forum has been invaluable source of info.

Thanks.
 

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WOW.....seeing this makes my day.....good for you !



After all the help and tips I've gotten from people to help me it's nice to see that I could spit out a correct diagnosis for someone.
 

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WOW.....seeing this makes my day.....good for you !



After all the help and tips I've gotten from people to help me it's nice to see that I could spit out a correct diagnosis for someone.


So I guess you will be looking for a larger helmet now.




Just kidding,,,good call Rick.
 

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I just got lucky on this one.....mine did the same thing when I first got the bike, the up and down idling and it was the boots.



Besides I already wear a LARGE
The cap comes apart with a flat head screw driver and there is a resistor inside. We recommend replacing the resistor with brass rod of the same size. At least look inside and see if it looks ugly. Just in case you didn't know
 
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