Topic: Emulsion Tubes

[jacob.thaler]

I have a 1976 CB550F and it had sat for a long time.  It's running now.  Needs some tweaking here and there.  As I was cleaning the carburetors and had the emulsion tubes out, it appears like the inside of the tubes are smooth and okay, but the outside of a couple of the tubes have been corroded as it sat all those years with the old varnish gas. Now there are grooves on outside of the tubes.  How important are the outsides of the tubes?  Is it only the inside that makes a difference?

[TwoTired]

It's the holes through the tubes that do the metering.  If the holes are erroded unevenly among the carbs, then the spark plugs can show dissimilar plug deposits, which makes tuning difficult.

[jacob.thaler]

Thank you.  That is good to know.  The holes looked okay. Now I don't have to try and find new tubes.  Just for future use, are the emulsion tubes the same for the K and the F CB 550?  I assume the needles are different because they have a different part number, but I am wondering for just the emulsion tubes.

[lucky]

You know I get really suspicious when someone starts a post that says they replaced emulsion tubes and then suddenly I see Ebay ads for emulsion tubes, people asking if they need new emulsion tubes.etc,etc.,.

Emulsion tube mania!

It is just a tube with holes people. No moving parts. You do not need to start getting out your magnifying glasses and start looking at all of your emulsion tubes for tiny defects!

[TwoTired]

It is just a tube with holes people. No moving parts. You do not need to start getting out your magnifying glasses and start looking at all of your emulsion tubes for tiny defects!

And you'd be wrong.  The emulsion tubes for the early style carbs have specific holes sizes that should not be enlarged by corrosion.  AND, the end of the tube has the needle jet orifice as part of the tube.  If either of these are damaged/altered, the carb will not behave as predicted.
This applies to the 627b, 022A, 069a, 087a, and probably the 649 carbs as well.

Just for future use, are the emulsion tubes the same for the K and the F CB 550?  I assume the needles are different because they have a different part number, but I am wondering for just the emulsion tubes.

The book says they are different.  I've not measured them myself.

Cheers,

[jacob.thaler]

Thanks for the info TwoTired.

[phil71]

Finally, we found something lucky will let slide!

[Spanner 1]

While were on the subject of emulsion tubes..... any thoughts on how far the e/tubes need to be screwed into the 'tube holder tower' in the carb body.... reason I ask is on my K1 750, it's not a 'set' position, i.e. the tube does not bottom-out or hit a stop and the tube shows more threads available when it's snugly tightened. Now won't the position of the needle jet ( top of the tube ) be critical to the needle metering, including ensuring the jet is fully closed @ idle by the needle taper.... see what I mean ? Any thoughts?

[bollingball]

Finally, we found something lucky will let slide!

He will be back

[trueblue]

Finally, we found something lucky will let slide!

I'm very surprised by this, from most of luckys posts he works by the same principal Adam Savage from Mythbusters does.

[TwoTired]

While were on the subject of emulsion tubes..... any thoughts on how far the e/tubes need to be screwed into the 'tube holder tower' in the carb body.... reason I ask is on my K1 750, it's not a 'set' position, i.e. the tube does not bottom-out or hit a stop and the tube shows more threads available when it's snugly tightened. Now won't the position of the needle jet ( top of the tube ) be critical to the needle metering, including ensuring the jet is fully closed @ idle by the needle taper.... see what I mean ? Any thoughts?

Now, I've never actually worked on a an early CB750 carb.  But, is was my understanding that the slide needle jet orifice was a separate part from the emulsion tube.  This would mean that the emulsion tube function does not directly relate to the slide needle metering, as long as the needle orifice/jet was in proper position.

The Cb550 carbs have the needle jet as part of the tube and it rests on a shoulder in the carb to correctly position the needle jet.

Perhaps someone can clarify exactly how the 750 carbs are different in this regard?   How dos the needle jet "register" position wise, in the early cb750 carbs?

Cheers,

[Spanner 1]

Went out to the garage and examined a carb... duuh, yes there is a separate needle jet in the carb throat, not the emulsion tube top which I thought protruded thru' the carb body, live and learn 
K0 - K6 carbs that is...
BUT... wear in the ( separate from the emulsion tube ) needle jet could be the cause of much slow running / rich idle problems and rich hesitation above idle throttle twisting.... this little part may not be given enough 'credence ' for mixture issues.... IMO.

[david 750f]

Spanner, I agree with you completely. The needle vibrates and eventually wears.

It is a big issue on Gold Wings that see high mileage.

My bike (50,000 miles) ran noticeably better when I replaced the needles with NOS Honda parts. 

[Deltarider]

Carbs 022A, 627B, 649A, 087A all share the same needle set (needle and tube) parts no. 16012-323-004. Needles have stamped on number 272304. These carbs are found on CB500, 500K1, 500K2, CB500K2[ED, F, G], CB550, CB550K1, CB550K2. Needle position may differ ofcourse.

Carbs 069A have needle set 16012-390-004 and are found on the models CB550F, CB550F1 and CB550F2. Needles have stamped on number 273004.

Needle sets 16012-323-004 and 16012-390-004 do differ, both needles as holes (smaller in the latter)

Above information concerns old style Keihins only.

[crazypj]

The through holes are either 0.022" or 0.023" diameter, I forget which

[Deltarider]

The through holes are either 0.022" or 0.023" diameter, I forget which

Not quite, in metric it's Ø 0,9 for the 16012-323-004 set and Ø 0,7 for the 16012-390-004 set.

[crazypj]

That would be about 0.028" and 0.036"
I meant the cross drillings, are you sure yours are that big? (someone hasn't attacked them with jet reamers?)

[Deltarider]

That would be about 0.028" and 0.036"
I meant the cross drillings, are you sure yours are that big? (someone hasn't attacked them with jet reamers?)

I have no reason to doubt the information given on p. 165 of the genuine Honda Shop Manual CB500-550.
Exception: above the left column it says 'CB500'. That's a mistake, it should be 'CB550'. 022A carbs were on the CB550 and CB550K1 (4 pipe models), not on any CB500.
It's about the only mistake in the manual.

[jacob.thaler]

I found something interesting for anyone who wants to know.  I was surfing around on the Sirius Consolidate, Inc website.  If anyone is looking for new (non OEM) emulsion tubes for their 550, Sirius refers to them as Main Nozzles. 

Check it out. 

HONDA CB550F CB550 F CARB MAIN NOZZLES 1975 - 1977  Part No.    JNH70C x 4

You'll have to do a search on their website.  I can't post external links.

[fmctm1sw]

That would be about 0.028" and 0.036"
I meant the cross drillings, are you sure yours are that big? (someone hasn't attacked them with jet reamers?)

This is how mine looked when I reamed them.  Then top is stock and the next one down is .040.

[lucky]

The emulsion tube is rarely a problem.
It is a tube with holes. End of story.


If it has grooves on it that is a matter of degree.  How deep are the grooves what do they look like??? I think grooves could get on the tube from a pair of pliers.
That is what i think.

The time when slide needles were very problamatic was on the CB77's and CB72's.
The needle was not allowed to "float" like the CB750, the needle was locked into the slide with a small screw and the needle and jet that, it went through were often out of alignment because the slides would get mixed up and put on the wrong carb body. What would happen was the jet the needle went in and out of and the needle would get worn on one side. When new needles and needle jets were installed the results were very dramatic. There was a special procedure to get the slide needle centered in the needle jet. Glad those days are over.

Those non"floating"needles were discontinued long ago. The ones in the CB750 are the "FLOATING" type and center themselves. Look inside the bottom of the slide and you will see that the pocket in the slide is larger that the C clip allowing the needle to shift so that it can center itself in the jet.

[Duanob]

Lucky couldn't just let the needle jet issue "slide" could he.