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Discussion Starter · #1 ·
Hello everyone
Have a project 1980 CX500 Custom I've been working on for a couple months now and trying to get it running properly. As of now it starts with the choke on and idles. As soon as I accelerate it dies. I have also seen some white smoke being spit out of the carbs. Ive been messing around with the mixture screw and the white smoke has stopped.

Currently I'm running velocity stacks and it is straight piped so Im guessing rejetting is in order. Does anybody know what the correct set up of jets would be for it to run properly? Any info would be greatly appreciated, its my first time rejetting so I'm lost on this subject.

Thanks for the help!
 

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The recommended jetting for pod filters with free-flowing exhaust is 90/120. You might start there and see if it runs OK. If it is idling good with the choke off that is a good sign. The smoke coming out the back of the carbs is fuel vapor and is normal. For more on the theory of jetting carbs http://amalcarb.co.uk/downloadfiles/amal/amal_tuning_guide.pdf
 

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Thanks for not helping Murray. If you know of a better guide to the theory of rejetting then post it. If you know what jetting will make his bike run properly then post it. The amal guide is what I learned from 35 years ago when I was a newb. This post was on the forum for many hours with no reply - I was just trying to help.
 

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I assume you still have CV carbs? You may have a hard time getting enough vacuum signal to get the slides to open all the way with velocity stacks. If you want to keep the stack look (and add some filter protection) you can buy some stack filter caps, which might make your life a little easier. Otherwise, you're getting into about the most complicated part of CV carb tuning, which is getting the slides to work right for decent throttle response.

If you want to dive into it, start with the pod filter recommendations. That should get you riding passably, and work your way down from the top. i.e. get the main jet figured out (WOT pulls) followed by the needle, then the pilot. Of course, make sure the bike is fully warmed up before doing any of that, and be sure you've got the carbs balanced before doing anything at all. do some research on "plug chops" and "reading plugs" to get you in the ballpark; lots of documentation out there on that stuff. Expect to go through some iterations.

Or you could probably find some pretty solid posts searching murrayf's username, I would imagine. :D
 

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Velocity stacks on CV carbs are going to be a bear. There will be next to no vacuum to lift the needle pistons. I'm sure you could make it run and get down the road but if you are after performance over looks I suggest PMing MurrayF about some Mikunis. If you ask nicely he may even custom tune them for velocity stacks instead of the K&N filters they usually come with.

That said, if looks are the important part and performance takes a backseat (which is fine, IMO, as long as you aren't compromising safety by doing stuff like removing the front fender) I'd grab #90 and #120 jets and go from there. A color-tuning kit is a bit on the expensive side (I believe around $35USD on eBay) but seems to be far, far easier and reliable than plug chops for finding areas where you could be dangerously lean.

If your bike came with an airbox, or if you have one available, I would put it back on for the moment and make sure your carbs work properly with it in place. Rule out any other issues (clogged slow jets, which are a press-in affair that requires tapping threads into in order to pull out, is what I'm battling right now) that could cause runability issues before changing the bike too far from stock. Make sure it idles and revs properly, then start swapping intakes and jets around. Of course, if the bike never came with an airbox from whoever you bought it from just go ahead and jump right in I suppose.
 

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Discussion Starter · #8 ·
Another question. Where can I find the #90 slow jet? I have been searching and only found #80 jets. If i can't find it would 120/80 be ok to use?
 

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Another question. Where can I find the #90 slow jet? I have been searching and only found #80 jets. If i can't find it would 120/80 be ok to use?
The #90 you want is a "main jet". CX500 carbs are a bit odd in that they have two main jets. I suggest ordering from JetsRUs. It will be a bit more pricey than ebay or amazon but you're getting a quality component guaranteed to actually be the size you ordered even if you go for the less expensive "OEM Equivalent"

https://www.jetsrus.com/a_jet_kit_street/honda_500_CX500_1978-1979.htm

You'll want #90 and #120 from the second list, "Main Jets"
 
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