Topic: CB550/4 Carb Problems?

[grapppa]

I have a 74 Cb550 whose carbs I just rebuilt.  Mounted them up and there are a couple of problems.  They have been thoroughly disassembled and cleaned and all new o=rings installed.  Heres my first question.  Can the tube under the main jet be removed. The needle extends into the tube.  I have read that on other carbs this is cross drilled. This is the only component that I could not remove and if it can be removed, I would guess that its clogged up as the carbs were all gummed up before I started working on them.  If they can be removed, any advice - I tried to tap them out from below but they did not want to move.

The symptom is that the bike coughs at 4500-5000 rpm and wont rev higher under load.

Thanks.

[TwoTired]

The tube behind the main jet is called an emulsion tube.  It comes out the hole where the main jet sits.  The slides are normally removed to press/tap these out from that side.  Care must be taken as that hole is a fuel metering hole whose shape is critical. Carb synch will be neccessary afterwards.

Can you read the plug deposits on the spark plug center electrode insulator?
Any changes to exhaust or air filter from stock?
Spark plug numbers?
Have you done everything else on the complete and thorough tune up list?

[paulages]

i just removed my emulsion tubes by blowing copressed air through the end of the circuit, where it opens up into the inner throat of the carb. if you look at the carb from the front (engine side), there is a little hole on the bottom side of the opening. unless they are really crudded in there, compressed air will blow them out. be careful, they'll shoot!

or, if you have the top end of the carb removed and can do what two tired suggests, gently punch them out with something soft, like plastic. he knows a hell of a lot more about these carbs than i do, so listen to him!!

[grapppa]

As I was eagerly awaiting someone to reply I looked very closely at a parts diagram and noticed this emulsion tube that has been mentioned.  Well, I think I was trying to remove it from the wrong end    Well, off come the carbs again and I will report back. Thanks so much for your replies. 

[grapppa]

Houston - Emulsion tube or needle set -whatever it is called is removed!  I used a 1/8" drill bit as a punch - worked perfectly.  And yes, were they clogged up !  More later....

[grapppa]

OK..So I cleaned up the emulsion tube...rechecked the float height (because they were leaking all over the place) to 22mm as per spec.  Remounted carbs - left off the air cleaner.  Then I checked the valve clearances using the go-no go method and got them to spec.  Started it up and sounded the same.  And the throttle response was exactly as it was before - except the floats no longer leak...which is some progress I bet.  Note that I did no carb sync and have no idea even how to get them close to spec.  I do not have a carb sync tool (sold it with my old Alfa Romeo 10 years ago).

What happens is the engine will rev under load to 3500-rpm then starts to cough and break up as it revs higher. Could it be starved for fuel?  And how to fix?

[grapppa]

Over the past 2 weeks I replaced the whole set of carbs and rebuilt them.  Hooked up the gas. Hit the starter.....and it lit right up and sounds great   All of the problems I had - erratic idle - coughing over 4-5000 rpm and #4 not firing.  ALL SOLVED. I am now stoked and will go for a short ride to check it out. I am one happy camper 

[SteveD CB500F]

When you say that you replaced and rebuilt the carbs, do you mean that you bought a spare set?
So you've no idea what was wrong with the old ones?

I've just bought a set for my 500 and plan to do just that over the winter. See thread "Carb rebuild pics"

[grapppa]

I bought a set of carbs on ebay for $30.  A nice buy as they were in very good condition.  I mixed and matched some parts from my old carbs and eventually put together a very nice set in the end. 

The original carbs had corrosion on the part of the carb that holds the main jet which caused a rich condition. This was due to gas seeping past the o=rings because the seal was not good.  When I say corrosion, what I mean is that the metal was literally corroded away and material is lost on the leading edge of the carb.  I would guess that when carbs sit around for a long time with gas in them, as the gas breaks down I would surmise that all sorts of nasty acids result which cause the corrosion.  It will pit the brass balls pressed into the area just above the float bowl on the interior.

[Dennis]

ALL SOLVED. I am now stoked and will go for a short ride to check it out. I am one happy camper

So tell us, Paul ......
    did you ride it?           

[SteveD CB500F]

Hmm.

I'll bear what you say in mind when I start my own "voyage of dioscovery through the 627s

Steve

[ddrink]

I bought a set of carbs on ebay for $30.  A nice buy as they were in very good condition.  I mixed and matched some parts from my old carbs and eventually put together a very nice set in the end. 

The original carbs had corrosion on the part of the carb that holds the main jet which caused a rich condition. This was due to gas seeping past the o=rings because the seal was not good.  When I say corrosion, what I mean is that the metal was literally corroded away and material is lost on the leading edge of the carb.  I would guess that when carbs sit around for a long time with gas in them, as the gas breaks down I would surmise that all sorts of nasty acids result which cause the corrosion.  It will pit the brass balls pressed into the area just above the float bowl on the interior.

Can anyone else comment on this?  I've been having the same issue with the revs.  I've had the carbs off 4x, everytime they go back on I have the same issue.  I would hate to pull and put them back on if it's not going to do any good.