[kansas 79 custom]

Recently when slowing down I'm getting intermittent popping and cracking out of the exhaust. At times very loud. Also, idle speed is diminished and I had to re-adjust it. The popping doesn't always happen, and other than that, starting, acceleration, and performance is fine. In-line fuel filter is clean.

 

[Bryan]

Sounds like a classic case of perforated air cut off valves. From my experience no harm will come to the bike if they're not changed immediately.

 

[Abes_CW]

Check the color of your plugs. popping is idicative of lean. Plugs would be white.



Could be ACV's, they can be easily and freely bypassed.

 

[Blue Fox]

It sounds like one or both of your ACV valves have gone south. They are the little diaphram thingies on the side of the carb. The left one is easy to access, the right one, not so easy without carb removal. Take the easy one off first and check for perforations. You can either replace the diaphrams, or block off the O ring under the cover. If you block the O ring off, open up your idle mixture screw a little. These valves were EPA mandated to allow for lean mixtures. There shouldn't be any harm in blocking these off.

 

[kansas 79 custom]

Check the color of your plugs. popping is idicative of lean. Plugs would be white.



Could be ACV's, they can be easily and freely bypassed.

Will do. Hasn't been that long since I kitted the carbs. No mixture screws on these carbs BTW.

 

[Shep]

Also check for leaks in the exhaust.These can cause backfiring/problems.

 

[mindactivated]

I have the exact same symptoms on my 1980 cx500D. Granted it has straight pipes, is not rejetted, although I have harley 883 sportster mufflers that I'm looking to get put on as soon as possible.



What's an ACV... Air Cut off Valve?



My fuel vent hole is fine, inline filter is fine, and there are no kinks in the hose. I know this only because I drained my gas and put in brand new stuff.

 

[Abes_CW]

Will do. Hasn't been that long since I kitted the carbs. No mixture screws on these carbs BTW.

No mixture screws?

 

[kingston73]

No mixture screws?

That's what I was about to say also.  Did you put on a set of mystery carbs?  Far as I know all the CX's had the same basic type of CV carbs, with or without the vacuum line but all had mix screws.

 

[kansas 79 custom]

Original factory carbs without any external adjustments except for idle screw.

 

[Shep]

Original factory carbs without any external adjustments except for idle screw.

Are you sure?



Check this parts fiche,



http://www.cmsnl.com/honda-cx500c-custom-1979-us_model631/partslist/E++22.html

 

[Abes_CW]

Original factory carbs without any external adjustments except for idle screw.

Probably still has the limiting tabs on them, (USA only spec) but they gotta be there.

 

[kansas 79 custom]

Probably still has the limiting tabs on them, (USA only spec) but they gotta be there.

Thanks for your comments. Can someone send me a photo or 2 of their carbs? I can't make much from the fiche. I'll post a photo of mine later to compare.

Please and thank you.

 

[Abes_CW]

Thanks for your comments. Can someone send me a photo or 2 of their carbs? I can't make much from the fiche. I'll post a photo of mine later to compare.

Please and thank you.

It's #6 on the fiche.

 

[kansas 79 custom]

It's #6 on the fiche.

OK, thanks. That definately helps. I'll have to check that out tonight. Didn't ride it to work today. Too blasted hot outside! Actual 102 deg. F, heat index 109!

 

[kansas 79 custom]

OK, thanks. That definately helps. I'll have to check that out tonight. Didn't ride it to work today. Too blasted hot outside! Actual 102 deg. F, heat index 109!

Now it's 8:30pm and only 100 deg. I looked and sure enough, I do have adjustment screws! Now I need to get a short screwdriver or flexible shaft one to do some adjusting. I checked the easy (left) carb ACV and it's good. Thanks for helping.

 

[saltwatersurf]

I'm having the same issues.

Blue Fox, to bypass the ACV, I block off the tiny hole that a tiny O ring goes around? With what? JB Weld?

 

[Shep]

I'm having the same issues.

Blue Fox, to bypass the ACV, I block off the tiny hole that a tiny O ring goes around? With what? JB Weld?

I have a set of cheap leather punches I use to make my gaskets,



http://globalcxglvtwins.hostingdelivered.com/viewtopic.php?f=10&t=256



http://cgi.ebay.com/6pcs-Leather-Craft-Hole-Punch-Set-LOW-SHIP-/140437112947?pt=LH_DefaultDomain_0



and punched circle of inner tube rubber using the smallest out of an old bit of inner tube.



HTH

 

[kansas 79 custom]

I have a set of cheap leather punches I use to make my gaskets,



http://globalcxglvtw....php?f=10&t=256



http://cgi.ebay.com/...DefaultDomain_0



and punched circle of inner tube rubber using the smallest out of an old bit of inner tube.



HTH

Great advice! Still troubleshooting my minor issues. I can't believe I missed the air screws! Maybe I really am a 'Newbie'.

 

[Abes_CW]

I'm having the same issues.

Blue Fox, to bypass the ACV, I block off the tiny hole that a tiny O ring goes around? With what? JB Weld?

cut a piece of rubber to size. It's a vacuum port, that on high signal pulls the diaphragm and stem up, blocking one of the air passages, quickly richening the mixture. Necessary if you leave your carbs at factory lean, but not if you richen them up slightly. I think I am running 2 turns out.



I wouldn't use JB, it's fairly permament, and you run the risk of foreign debris blocking places you don't want blocked. IMO.