Topic: Replace CB500 carb with CB550

[mustanger67]

I recently bought a low mileage "72" CB500.  The bike ran like poop so I took it to my friendly mechanic.  He tells me the carburetors have corrosion in them so bad they will need to be replaced.  I'm having trouble finding used 500 carbs.  What are the odds of the 550 carbs working o.k.?  Thanks, Jerry 

[Bob Wessner]

He tells me the carburetors have corrosion in them so bad they will need to be replaced.

What kind of corrosion and where in the carb set?

[mustanger67]

I'm not much of a mechanic, but he told me it was inside the carbs where a o-ring comes into contact with the needle valve.  (I think).  Sorry if I didn't describe it correctly.  It will be tomorrow before I can ask him again.  Thanks, Jerry

[Bob Wessner]

Since I'm not familiar with the 500 carbs, I'm sure someone who is will give you better advice. One thing to consider is that truly "new" carbs are unlikely so you are talking about perhaps a set off eBay or something and they may not be in any better condition. Did the mechanic even suggest stripping them down, cleaning and replacing needed parts? Have you considered trying to do this yourself, or are you not comfortable with that?

[Jay B]

where a o-ring comes into contact with the needle valve. 

I've never seen this but I've heard of it happening. The carb body itself corrodes enough around the needle seat that it won't seal the O ring. If that is truly the case you'll need different carb bodies.

[mustanger67]

Jay,
 You hit the nail right on the head.  That's what he told me was wrong.  Yes I'm looking to replace the whole rack of carbs.  I'm not having any luck finding 500 carburetors but the 550 carbs seem to come up on e-bay fairly often.  Will they match up?  Thanks, Jerry

[SteveD CB500F]

I believe that the carb bodies are the same - only the jetting was different (to suit the 4-1 pipes).  This of course only applies to the 550F's - the later K3 models(4-4) used completely different carbs.  The attached picture is of a set of 627B carbs from a CB500.

[volz1fsu]

Yes it will work fine. 
I was running the 550 carbs on my 500 with no problem at all.  Even with the 550 jetting in it, I never had a problem with it.  Plugs were burning clean and all.  It had a lot of power too, that is the 500 that I got over 110mph.  Amazingly fast I thought.

[csendker]

There are some differences.  Check the Carb FAQ for the specs --> http://www.sohc4.us/forums/index.php?topic=5410.0

The carbs underwent some changes for the later years.  I think it would be best to stick with the 022A's or 069A's.  The PD series is where the changes came into play.  You also may need the matching manifolds.

[csendker]

This is another source --> http://www.motorcycleproject.com/motorcycle/text/specs.html

The carbs did change in 1977, thanks to the EPA.

[dusterdude]

o yea,you gotta love the epa

[TwoTired]

The carb bodies are stamped with a setup number indicating what internal components and settings were used.  The Cb500's were stamped 627B.   At least all of them that I have found.  These will work the best on a totally stock CB500.

The same carb bodies, with different internal setups, were used on the Cb550 (022A and 069A stampings) until the K models of 77-78 (PD series).  The setups coincide with the displacement and exhaust type changes found on other models of CB500/550 series.

If you still have stock exhaust and air filter components installed on the bike, DO seek out the 627B carbs.  If not, simply avoid the 77-78 PD carbs as they will not fit on your bike without other component changes as well.  The 022A and 069A carbs can be tuned to non-stock intake and exhausts, just as the 627B carbs can, and they fit interchangeably.

Cheers,

[mustanger67]

Thanks to everyone for the great information.  I now just need to find either some original 627B, 022A, or 069A carbs to replace my old ones.  Anyone have an extra good set laying around?  Thanks again, Jerry