Topic: CB550k Hanging Idle

[DaveBarbier]

In the video towards the end I say "fast idle" when I mean "fast idle cam".

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1978 Honda CB550K

[DaveBarbier]

In the above picture of the slide you can see the size of the space when it's resting. The bike seems to be idling now around 1000rpm when it's fully warm. This is the position of the slides at idle. They're synced so they're all the same. Not sure if they seem too open.


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1978 Honda CB550K

[DaveBarbier]

Just noticed that the tower that holds the main jet in carb number 1 is cracked a little.


Also, when I spray carb cleaner in one of the the galleys in the airbox side of the carb it shoots out the main jet. Hope that's not bad to do, I'm just making sure everything is clear. But the carb cleaner also seeps out from where the main jet holder threads are exposed on all carbs, not just the cracked one. Doesn't seal perfectly but not sure if it's supposed to.


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1978 Honda CB550K

[Dave Voss]

...But the carb cleaner also seeps out from where the main jet holder threads are exposed on all carbs, not just the cracked one. Doesn't seal perfectly but not sure if it's supposed to.

Those threads should provide an adequate seal, unless they are damaged or corroded.  Also, the main jets are supposed to have O-rings around them that seal against the recessed bore in the end of the holder, are those present and in good shape?  The vacuum that pulls fuel into the jets will leak everywhere that it can, disturbing the intended flow of fuel, so be sure that those connections are sealing as they should.

[Maurice]

Never noticed any o-ring inside the needle jet holder? At any rate, yeah, it doesn't sound like it should leak from the threads... These carb bodies look like they have seen better days. You could probably JB weld that crack.

Careful pulling out the pilot jets. Make sure you pull as straight as you can, no twisting or wiggling, and they're easy to crush if you use pliers.

[DaveBarbier]

...But the carb cleaner also seeps out from where the main jet holder threads are exposed on all carbs, not just the cracked one. Doesn't seal perfectly but not sure if it's supposed to.

Those threads should provide an adequate seal, unless they are damaged or corroded.  Also, the main jets are supposed to have O-rings around them that seal against the recessed bore in the end of the holder, are those present and in good shape?  The vacuum that pulls fuel into the jets will leak everywhere that it can, disturbing the intended flow of fuel, so be sure that those connections are sealing as they should.

There are zero o-rings where the main jets are. Do you mean there are supposed to be
o-rings where the screw driver is pointing or the pick?



This may sounds really stupid and a horrible idea, but could I used fuel safe Teflon tape to seal the main jet holder in the carb body? These are pretty corroded as you can see and if they're supposed to seal then I'm not sure what else to do. I'm pretty sure you mean there's supposed to be an o-ring between the holder and the main jet. I don't see how there could be an o-ring between the carb body and the main jet holder.


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1978 Honda CB550K

[DaveBarbier]

Never noticed any o-ring inside the needle jet holder?

Was that a question for me? No, I never noticed anything. But since some of the IMS had missing o-rings and also had washers and springs in the wrong order I wouldn't be surprised if I'm missing major components.

Careful pulling out the pilot jets. Make sure you pull as straight as you can, no twisting or wiggling, and they're easy to crush if you use pliers.

Thanks, yeah I pulled these out when I first rebuilt them. They came out pretty easily actually. Then I pushed them back in and used a wooden dowel to tap it so they gently seated.


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1978 Honda CB550K

[Maurice]

No, I mean to say I never noticed it. I don't think there's any, fiche doesn't show one either.

[DaveBarbier]

No, I mean to say I never noticed it. I don't think there's any, fiche doesn't show one either.

Ah ok, I see.

Also, the main jets are supposed to have O-rings around them that seal against the recessed bore in the end of the holder, are those present and in good shape?

Yeah I didn't see any either. Others maybe have an o-ring but the parts fiche doesn't show anything for these carbs.

http://images.cmsnl.com/img/partslists/honda-cb550k-1978-usa-carburetor-components-78_bighu0056e431801_09ce.gif




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1978 Honda CB550K

[harisuluv]

There is no oring for the main jet/emulsion tube assy for that model carb (PD style).  The oring is for the earlier style carb.

[DaveBarbier]

There is no oring for the main jet/emulsion tube assy for that model carb (PD style).  The oring is for the earlier style carb.

Thanks. Is there a need/way for me to seal the emulsion tube in the carb body like I mentioned a couple posts back?


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1978 Honda CB550K

[TwoTired]

There is no oring for the main jet/emulsion tube assy for that model carb (PD style).  The oring is for the earlier style carb.

Absolutely true.

To catch up on your other questions.
--You have bowls transplanted from another carb set.  That's why the drain screws faces the wrong way.  And, all the bowl nipples should be brass inserts like half of what have show.  I don't know why the transplants won't work, as long as they look the same inside the bowls among the four.

-- Don't worry about the groove in the choke shaft.  There's nothing that belong there on these carb sets.

--  I think maybe that your choke linkage is assembled wrong.  That marred tab you are concerned about should be engaged all the time.
I added a pic of my spare set so you can compare/verify.

-- The small nozzles at the carb throat entrance are air jets.  One feeds the emulsion tube chamber for the pilot jet, and the other feeds the main/throttle valve emulsion tube.  The fuel is thus emulsified with air before being fed into the carb throat.  Emulsified fuel draws more easily and atomizes faster.  Given the corroded state of your carbs, I'd be sure to verify there is no corrosion blockage or other restriction between the air jet and the pilot jet emulsion chamber.  Such a condition could support an over rich pilot circuit.

--The crack in the jet holder tower is of some concern.  Although it shouldn't be much of a factor at idle, at higher throttle setting it could alter the fuel mix, provided it is indeed leaking.  I think I'd send the carbs off to Jim to have the crack micro welded.

I don't recommend teflon tape to seal the treads.  Although, if you have the yellow type meant for gas exposure, perhaps it might help.  I think I'd put a bit of it in a jar with gasoline and watch if it turns to goo or have other physical changes over time.

[Dave Voss]

There are zero o-rings where the main jets are. Do you mean there are supposed to be
o-rings where the screw driver is pointing or the pick?

See the smaller diameter section on the main jet just below the head but before the external threads begin?  That area is machined to accept an O-ring, right where your pick is pointed.  I've taken more than one set of PD carbs apart, and they all had O-rings on the main jets, so I believe it is correct to use them there.

[DaveBarbier]

There are zero o-rings where the main jets are. Do you mean there are supposed to be
o-rings where the screw driver is pointing or the pick?

See the smaller diameter section on the main jet just below the head but before the external threads begin?  That area is machined to accept an O-ring, right where your pick is pointed.  I've taken more than one set of PD carbs apart, and they all had O-rings on the main jets, so I believe it is correct to use them there.

Yeah I see where you're saying. It does look like it can accept an o-ring. Mine don't leak from there though so I'm going to keep it as is. Right now I'm submerging some "gasoline safe" Teflon tape in gas and another piece in carb cleaner for the emulsion tube threads. Seeing as those would be the only chemicals that it could be in contact.


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1978 Honda CB550K

[TwoTired]

I'll say it again, the PD carbs do not have orings on the main jet.

Even Honda doesn't list an oring for that position.  No oring between #13 and #18.

http://www.cmsnl.com/honda-cb550k-1978-usa_model7222/partslist/E++1801.html#results

[Dave Voss]

I'll say it again, the PD carbs do not have orings on the main jet.

Even Honda doesn't list an oring for that position.  No oring between #13 and #18.

http://www.cmsnl.com/honda-cb550k-1978-usa_model7222/partslist/E++1801.html#results

Back in the day (like in the 1980s...) when new jets were ordered, they had the O-rings already on them, which may be why there isn't a separate part number for them.  Most new and aftermarket jets available today do not include them, and so they need to be sourced separately.

I'm not saying that you're wrong, or that I'm right, just that those particular jets and holders are machined to accommodate O-rings, which not only help provide a good seal, but also offer a bit of resistance to help prevent the jets from working loose, without having to over-tighten them.  This is a fairly common design and practice when working with jets, and I've seen multiple sets of PD carbs (without any screwdriver marks, so likely original) that all had O-rings in that location.

This is a relatively minor issue, and not one to over-think, but the design to accommodate O-rings is intentional, whether or not the choice is made to use them.  Just my two cents on the subject, from my experience playing with many carburetors on both motorcycles and automobiles...

[DaveBarbier]

--  I think maybe that your choke linkage is assembled wrong.  That marred tab you are concerned about should be engaged all the time.
I added a pic of my spare set so you can compare/verify.

The tab is only not following the rest if the assembly because I'm holding the butterfly open. It normally travels with the whole thing because of a spring.

Thanks, but I don't know if I can really tell from that picture. It seems like it's pretty much the same but if you look at this picture where the red line is, I'm sure that piece isn't supposed to be resting and gouging out the piece sticking off the carb body. That looks like more of a rest that the cable arm relaxes on...and mine is being hung up by that tabbed piece.





If you or anyone else would be so kind to post a couple more pictures from a couple angles that would be great. Nothing in the Clymer or Honda manuals say how it's assembled. But, all in all, my choke is opening and closing so maybe I'm over thinking it.

-- Given the corroded state of your carbs, I'd be sure to verify there is no corrosion blockage or other restriction between the air jet and the pilot jet emulsion chamber.  Such a condition could support an over rich pilot circuit.

I sprayed carb cleaner in those air jets and all seems clear.

I don't recommend teflon tape to seal the treads.  Although, if you have the yellow type meant for gas exposure, perhaps it might help.  I think I'd put a bit of it in a jar with gasoline and watch if it turns to goo or have other physical changes over time.

I have two pieces sitting in gas and carb cleaner as I stated before and so far...about an hour they're fine. I'll let them sit overnight I think and then dry them and see what happens.

Thanks everyone, really I can't say thank you enough. I owe you all beers or Manhattans or celery and peanut butter...whatever you're into.


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1978 Honda CB550K

[harisuluv]

I have done several hundred sets of carbs, I have never seen an oring on a PD carb set.  If that is not enough, I challenge you to find any Honda schematic that shows one on this style of carb (77-78 PD).  The emulsion tube/jet holder is the same as earlier CB750, which also do not have an oring. 

I think the fact that you have the main jet slightly unscrewed, that space between is being interpreted as... I don't know, a groove for the o-ring?  These jets are screw in type, not pressed in. 

Your choke linkage... how did that plastic piece get there.  It looks like the piece that is a bushing/spacer for the #2 slide arm.  It's not supposed to go there.

[DaveBarbier]

Your choke linkage... how did that plastic piece get there.  It looks like the piece that is a bushing/spacer for the #2 slide arm.  It's not supposed to go there.

Ugh, again this is showing that the PO did strange things to this rack of carbs. I wonder what else is wrong that I don't know that might be preventing them from functioning properly.

How did it get there? I have no idea. Other than that plastic piece, the choke linkage looks assembled correctly?


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1978 Honda CB550K

[DaveBarbier]

Your choke linkage... how did that plastic piece get there.  It looks like the piece that is a bushing/spacer for the #2 slide arm.  It's not supposed to go there.

#2 slide arm...is this what you're talking about?


I'm beginning to think if you had these carbs in front of you you'd have a heart attack.



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1978 Honda CB550K

[harisuluv]

As shown in the picture, to the left of the screw, see that gap there?  That's where that plastic piece goes.

If it were me I would get another set.  Corrosion and pitting, some abuse is maybe workable, but that crack on the emulsion holder, I would have at least replaced the body.  A better core can be had for not that much, you can rebuild it and actually learn about rebuilding carbs, not about damage that you can't fix or what the PO screwed up with.   And that's just what you can see.  I think it's possible that crack is from overtightening the emulsion tubes?  Even the brass is pitted, which is what you can see on the outside.  The inside can also be pitted and damaged, which would make those important holes bigger.

[Dave Voss]

Here is a picture of what I'm talking about.  The main jet has a reduced diameter straight section between the bottom of the slotted head and the top of the threads, where an O-ring is intended to be installed.  The jet holder/emulsion tube has a counterbore before the internal threads begin, which aligns with the O-ring on the main jet when it is installed.  As the main jet is tightened, the O-ring is gently compressed in that space to create a positive seal and to provide a bit of mild tension to help prevent the main jet from loosening.

This is the design of these components, regardless of whether or not a particular manufacturer illustrates it in a diagram, or an individual carburetor rebuilder has ever seen it.  Forums like this work best when members are open to learning from each other, rather than trying to convince others that they must be mistaken.  The design features of these components are obvious and speak for themselves, I'm just trying to encourage others to observe, listen, and possibly learn.

[harisuluv]

I understand what you're saying, but you're not simply encouraging others to observe, listen, and possibly learn, when you are explicitly saying they are missing a part.

You could point to the "design" andn existing accelerator pump circuits sans the machining and nozzles--yet they are still not missing anything. 

The application it's used in is all that matters.  If there were a bike that called for a jet the exact size of the opening in the emulsifier tube, would you be telling them they are missing a jet and an oring?  After all, that's what design would point to right?

[TwoTired]

Forums like this work best when members are open to learning from each other, rather than trying to convince others that they must be mistaken. 

...which "rather" seems to be your goal.

Are you seriously asserting that the op's carb problems will be solved by adding an oring to the main jet?  Or, is there some other form of help you are offering?

Have you considered that, even if it were originally designed to accept an oring, that production models eliminated it as unneeded or unnecessary for proper and correct operation?

It does make me wonder how all the PD carbs I've seen without orings on the main run so well...even when I've clearly been doing it wrong for all these years.

I'll step aside and let the "experts" help Dave B get his carbs "correctly" sorted.

[Dave Voss]

I understand what you're saying, but you're not simply encouraging others to observe, listen, and possibly learn, when you are explicitly saying they are missing a part.

The application it's used in is all that matters.  If there were a bike that called for a jet the exact size of the opening in the emulsifier tube, would you be telling them they are missing a jet and an oring?  After all, that's what design would point to right?

Yes, actually I would, because the end of the emulsifier tube is at a different elevation (relative height) than the head of the jet, which changes the column length that fuel is drawn through, and that will affect the resulting mixture.  As an experienced carburetor rebuilder, you already know that, so maybe we can avoid diving in this direction, as I'm sure we're both just trying to help the OP.