Topic: CB550k Hanging Idle

[Dave Voss]

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?

Initially, I suggested checking valve clearances and dynamic compression, because trying to synch carbs on an engine that is not well sorted mechanically can be a waste of time.  Later, when the OP stated that he noted leakage around the main jets, I stated that the holder threads shouldn't leak, and also suggested that he check the presence and condition of O-rings around the main jets, not knowing whether or not his carbs actually had any installed.

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?

This is entirely possible, as I'm sure happens all the time in manufacturing.  I'm not disagreeing with the fact that main jets and holders in good condition can seal adequately without needing O-rings, but the OP's carbs do not appear to be in good condition, and a specific comment was made regarding that fact that they appeared to be leaking, and so in this case suggesting that O-rings be used as originally intended by the designer of the jets/holders seemed to be good advice.

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.

Nobody said you were wrong, see above...  I just find it interesting that the carbs that came on my '78 CB550 had O-rings on the main jets, and the spare rack of carbs (same model) that I bought also had O-rings on the main jets.  That tells me that although it may in fact be statistically unusual, it at least shows that I'm not the only person who feels that the use of O-rings on the main jets is a good idea.

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

Your experience and expertise here are invaluable, you've helped me on several occasions which I greatly appreciate, and you are decidedly one of the resident experts, so I hope you aren't serious about stepping aside on this thread.  My suggestion to use an O-ring in a location that others feel is optional or unnecessary shouldn't be the source of any conflict.  I'm only offering a suggestion based on the original design of those components, which the OP can try if he wants to.

[harisuluv]

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.
[/quote]

You really missed the point, and that is why I said "a bike," a fictional hypothetical bike.  You don't know what the specs for are for this bike, cause it is governed by the application.  How about this, look at all those exposed threads on the main jet holder, they are "designed" like that for a reason aren't they?  Better screw them ALL the way in, cause that's what Kei Hin intended.  On this set of carbs it WOULD change the height of the jet, that is why HONDA supersedes any remnants of design or intent by Kei Hin.   

Really what you have offered is a factoid about Kei Hin's design.  It is irrelevant to our use.  It serves as misinformation to our application and is not being offered up as the bit of trivia that it is, but the "real" and "genuine" use for OUR application. 

[Dave Voss]

How about this, look at all those exposed threads on the main jet holder, they are "designed" like that for a reason aren't they?  Better screw them ALL the way in, cause that's what Kei Hin intended.  On this set of carbs it WOULD change the height of the jet, that is why HONDA supersedes any remnants of design or intent by Kei Hin.

Of course the main jet needs to be screwed in all the way, until the underside of the head is flush with the end of the holder,  Once in that position, the presence or absence of an O-ring cannot be determined, because the space that it occupies is completely internal.  In other words, the O-ring does not change the position of the main jet, its either there or its not.  I believe the OP's picture showed the main jet partially unscrewed to illustrate the question regarding where it would be if there was one.  Was this picture (or my explanation) misunderstood?

Really what you have offered is a factoid about Kei Hin's design.

I'll agree with that statement.

It is irrelevant to our use.

Perhaps when all of our motorcycles were new, but they are not, and in fact the OP's appears to have been the subject of some neglect over the years, and so the presence of O-rings might offer a better seal than the worn and possibly corroded threads can provide.

It serves as misinformation to our application and is not being offered up as the bit of trivia that it is, but the "real" and "genuine" use for OUR application.

I never used the words "real" or "genuine", only that the original design intent was to incorporate an O-ring, and that in this particular situation, it might be worth considering.  This really isn't any different than encouraging someone to use sealer on a gasket that would normally be installed dry for a joint that could leak, or to use a lock washer or double nuts on a stud to prevent the loss of whatever part it is holding on, neither of which may be considered in keeping with the manufacturer's design, but both might actually fix the issue.

If we agree that the use of an O-ring between the main jet and its holder is something that Keihin incorporated a provision for, then at least its an option for others to decide whether or not to use.  Honda may have decided it wasn't necessary.  Others may decide that it still isn't necessary.  But the option still exists, and in the context of the OP's carburetor issues, sharing information about it is a good thing, so I did.  I don't understand the effort to try to stamp this out.

[harisuluv]

How about this, look at all those exposed threads on the main jet holder, they are "designed" like that for a reason aren't they?  Better screw them ALL the way in, cause that's what Kei Hin intended.  On this set of carbs it WOULD change the height of the jet, that is why HONDA supersedes any remnants of design or intent by Kei Hin.

Of course the main jet needs to be screwed in all the way, until the underside of the head is flush with the end of the holder,  Once in that position, the presence or absence of an O-ring cannot be determined, because the space that it occupies is completely internal.  In other words, the O-ring does not change the position of the main jet, its either there or its not.  I believe the OP's picture showed the main jet partially unscrewed to illustrate the question regarding where it would be if there was one.  Was this picture (or my explanation) misunderstood?

I misunderstood nothing, you have misunderstood me though, I did not say main jet, I said main jet holder. 

It serves as misinformation to our application and is not being offered up as the bit of trivia that it is, but the "real" and "genuine" use for OUR application.

I never used the words "real" or "genuine", only that the original design intent was to incorporate an O-ring, and that in this particular situation, it might be worth considering.  This really isn't any different than encouraging someone to use sealer on a gasket that would normally be installed dry for a joint that could leak, or to use a lock washer or double nuts on a stud to prevent the loss of whatever part it is holding on, neither of which may be considered in keeping with the manufacturer's design, but both might actually fix the issue.

No you just made assertions without any qualifiers such as:

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.

Perhaps when all of our motorcycles were new, but they are not, and in fact the OP's appears to have been the subject of some neglect over the years, and so the presence of O-rings might offer a better seal than the worn and possibly corroded threads can provide.

You saw this picture and then mentioned o-rings.  The guy has a crack in his emulsion tube holder.

Honda may have decided it wasn't necessary.

Honda decided it wasn't necessary.

Really what you have offered is a factoid about Kei Hin's design.

I'll agree with that statement.

Ok, factoid acknowledged.  Now if your analogy is true, you have a lot of work to do in other threads telling people that they are missing gasket sealer and locknut washers.

[Dave Voss]

Now if your analogy is true, you have a lot of work to do in other threads telling people that they are missing gasket sealer and locknut washers.

I thought we were all grown-ups here, but given your repeated attempts to tear apart the information that I have to offer, I guess not.  I've been trying to explain why an O-ring might be useful.  You seem overly interested in proving that I'm wrong, and your cyber-courage is showing.  Frankly it doesn't really matter that much to me, so let's just say that your mission is accomplished.

"If you think you're an expert, you've probably stopped learning..."

Peace...

[DaveBarbier]

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.

Thanks James, I sent you a PM.

And thanks everyone. When I decide what I want to do I'll let you guys know how it works out.

As for the yellow fuel safe Teflon...I let one piece sit overnight in gas and another in carb cleaner. Nothing turned to goop and after I dried it off it looked normal. Seems safe enough to me.


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1978 Honda CB550K

[Ceebeehead]

Mind if I resurrect this topic? Any solution to your problem? I just put 4 into 1 headers with a baffled exhaust and I'm ready to sync and tune the carbs due to a hanging idle around 3k rpm. So far I have the needles one clip richer and I've gained a bunch of power from 1/4 throttle on but I have some hesitation from a stop. Now I think I have to tweak the idle mixture screws some. Fun! Hope you got yours sorted out.