Honda CX 500 Forum banner
1 - 20 of 28 Posts

·
Registered
Joined
·
1,556 Posts
Discussion Starter · #1 ·
Just bought Larry's book (yesterday) and I have not read it yet (will get it soon).

I am concerned about the two carbs being different.

One looks like it was previously opened and might have had the jets replaced. The other looks stock. Based on how filthy it was I could believe it was never cleaned.

I bought two carb kits that include jets. Should I replace the jets in both carbs so they are identical or does it matter?

Thanks



Oh if the profile does not show:

1978 CX500

Kennesaw GA
 

·
Super Moderator
Joined
·
2,851 Posts
Hi Tony, your book is on the way.

As for the jets, most after market jets are marked on the top on the jet. Keihin jets are marked on the side. If both are on the side, and they are 78 & 112 jet sizes, then clean them up and use them again. I always prefer OEM.

Larry
 

·
Registered
Joined
·
810 Posts
I'd look closely at the jets when you pull them to make sure they are numbered the same. When I pulled the carbs on my CX one looked a lot dirtier than the other everything matched otherwise. I can say you def would not want to have differing jets in those carbs.
 

·
Registered
Joined
·
1,556 Posts
Discussion Starter · #4 ·
Thanks a lot again!

I did not see any markings on the top so I think theses are OEM.

I got lucky!
 

·
Registered
Joined
·
1,163 Posts
Be careful, look close.....and DON'T drop one on a gravel floor..........Don't ask me how I know.........lol



And you DO want those jets to be the same.....Methinks OEM size is 78-112.
 

·
Registered
Joined
·
45 Posts
Another thing to check, and i found this out by accident years ago was to check your sliders, look on the top of them, you have a number, make sure it is the same on both carbs, most are not, you will be surprised at the difference it makes, i think it relates to the weight or some-thing along those lines, unless some-one else knows different.
 

·
Super Moderator
Joined
·
2,851 Posts
I'm sorry guys, I forgot to mark this one to be notified when a new post was added.



First off I forgot to mention to Tony that to verify both carbs are the same, check the VB # stamped at the edge of each bowl. Both carbs should have the same #. If not, they shouldn't be together. Someone made a pair up. I tried it once and it didn't work out.



CXPHREAk, The ID #'s on the slides are under the lip of them. On the CX, GL500's it usually a capital "B" and nothing else. No #s were used on them that I have found. Now, the GL/CX 650's are marked with the "B" also, but on the top of the slide is "004" cast in the top. This statement has been changed by my research in post # 18 below.

I haven't gotten into the weight of them yet because I have always made sure the IDs match in a set of carb slides. With that point being brought up, I will go pick up a scale and weigh a bunch of slides. I'll get back here when I do OK. I promise.



cdyoung, It depends on what pipes you put on. If it's a stock style there's no need to jet obviously. Even installing a set of Harley sportster or Dyna pipes won't require a change. But if you go with headers or straight pipe then you would need to re jet. All that also depends on if you keep the stock air cleaner or swap that out too for pods. There are so many different combination's to choose from. One of these days I'm going to dedicate some time to put all the possible combos on one of my bikes and work with what the jetting's will or should be. But until I get my two project bikes done and sold I'm focusing on them first. I have already bought a set of Mac's to test with.
 

·
Super Moderator
Joined
·
2,851 Posts
I'm getting the Mac 2-1 and removing the baffles, and keeping the stock air box for what it's worth...


So far the best success with that combination has been 90/120 jets and turning the mixture out to 3 or 3 1/2 turns. Keeping the stock air box in my opinion is a wise move.
 

·
Registered
Joined
·
84 Posts
Since I just happen to have my carbs all torn apart right now, I looked and the jets are #78-#112 and the slides are marked "B". I do not think these carbs have ever been apart before. They were not as bad as I was expecting, but definitely had rust pockets in them and various things plugged up.
 

·
Registered
Joined
·
1,164 Posts
Since I just happen to have my carbs all torn apart right now, I looked and the jets are #78-#112 and the slides are marked "B". I do not think these carbs have ever been apart before. They were not as bad as I was expecting, but definitely had rust pockets in them and various things plugged up.
I believe that's the normal stock jets for the 500's after 78 or 79, that's what my 80 and 81 have
 

·
Super Moderator
Joined
·
2,851 Posts
All the GL500s had 78/112 as well as the 78-79 standards and deluxe. The 80 and up std. and custom CXs have 78/115.



While I'm at this, I might as well tell you that the slide needles are different sizes in each model too. The 78-78 models without the pumps use a 24B needle. The 80 and up carbs use a 53F needle. The 24B is thicker at the tip than the 53F is. So, if your running the early carbs and need a bit more fuel at the top end you can swap out the needle for the 53F to enrich the mixture over the 5K rpm mark.



BTW, a thinner needle at the tip would be like putting in a bigger jet.



This is one of the variables that I will be working on when I get time to start playing with re jetting. There are several sizes of needles used in all the different models of the CX/GL bikes. I have been keeping a list of each # and the size of each one so that when I get into the project I'll have a better idea of what I can use to fine tune a set of carbs.
 
  • Like
Reactions: zinnia

·
Registered
Joined
·
2,601 Posts
Keeping the stock air box in my opinion is a wise move.



Agreed. These are vacuum slide CV carbs and very picky. Even a K&N air filter can upset them as well as exhaust alterations. These bikes were set up for max performance stock, the only way you can get anything more out of them is to regrind the cams and do one heck of a lot of tuning. Want more power? Put a down payment on one of the newer pocket rockets or one of those Suzuki Kowabubgas but don't expect to ever be able to work on it yourself, probably the cost of a good CX/GL just to have it in there.
 

·
Super Moderator
Joined
·
2,851 Posts
OK guys, as promised I went out and got a digital scale today and weighed 28 slides for the CX/GL carbs. Yes, I have that many and more. What I found was that ALL the slides no matter if they had a number 1 or 2 or no number on top were extremely close to each other in weight. They all had the letter "B" under the top.



And I need to go up and amend my other post saying they didn't have any markings on the top. MOST don't. That I think is because it's where they machined the weight out of them to get them down to what they wanted. Some of the ones I pulled out of the extras box did show a number 1 or 2 cast into the top. Those had not need much if any machining to achieve the weight.



OK, ALL the CX/GL500 slides weighed out between 2.41 to 2.44 ounces. Or, 68.2 to 69.3 grams. There was no majority group in these measurement. I ended up with 3 fairly even rows of slides in the following weights. 2.41, 2.43 and 2.44 ounces. To give you an idea of the weight difference in them, a #10 Exacto blade weighs just 0.02 ounces. That's how much difference there was between all the slides.



Now, the CX/GL650 slides surprised me. They weighed less. 2.38 to 2.39 ounces. That was for all 10 slide I have for them. It would seem they wanted the slides to open fast when the designed the 650's.



So, finding a major difference in the weight of slides isn't there. They all came out too close to make any difference in the performance of one of our bikes. It was an interesting thing to find out for sure though. I'll be using this scale a lot more though as I get other sets to do. If I ever find a different type of slide for the CX I'll let you know. But so far even the arch at the bottom of the slide that goes inside the venturi's have all been the same too.



One interesting thought here though is the lesser weight of the 650 slides. It may not be much difference, but it MAY give a faster transition to top end if your looking for the top end speed advantage. Maybe when I start the jetting project I'll lighten up a set of slides when the jetting is set on a set of carbs and see what the effect is. I can see that project taking a long time with all the possibilities and combination's.



Thanks odie for the thought and suggestion of the slides weight difference. Now we know.

Larry
 

·
Registered
Joined
·
1,164 Posts
I was going to ask about the 650 slides in the 500 carbs, but you covered it, you really are a carb genius!!! Thanks for your work and dedication, it really helps a lot of people!
 

·
Super Moderator
Joined
·
2,851 Posts
Things like this make it fun. I can't wait to get my two bikes painted so I can work on the jetting and combo possibilities.



Just a little hint of what I'm thinking on the jetting issues. Most complain about no response when they add headers. So they add bigger jets. My theory is that if you go from a 78 to say an 80 or 85, and then drill out the low jet from .018" to .020", that would work in the lower to 5K transition rpm instead of OVER jetting the whole thing to compensate for the too small low jet. Then not only would you get a much better throttle response, but you MPG would, or should go up. Now you see why I'm saying it's going to take some dedicated time to do this. There are so many possibilities to come up with the right package for jetting.



Thanks for the compliment. But I'm no genius trust me. I'm just one of the guys that's anal enough to get way to deep into what needs to be figured out. I enjoy it.

Larry
 
1 - 20 of 28 Posts
Top