Topic: Carbs agian

[M3JOC]

Hello All, New to this fourm but have looked at a lot of the posts and read the FAQ`s, now with this in mind i`m looking for some advice.

Bike is a Honda CB550 1974, engine is sound, timing done, valve clearance`s done. now its time for the carbs, I`ve done a total rebuild cause they were full of muck, all the passageways are now clear, new air screws, new pilot jets (38) new mains(98) new needles (clip one up from the bottom), float heights set at 22mm, straight through 4 into one pipe (slashcut end pipe with no baffle) and K`n`N type filters, one per carb (069`s).

Now the question, I can set the mixture pretty much spot on for the first third of the throttle, mid range is lean, and full throttle is very very lean (stop now before you hole a piston lean). So the mains need changing up a bit. What size do i go for as a starting point?? I am thinking of 105 but looking at how lean it is i also think 110, do any of you guys have a best guess as to where to start, i know it will be trial and error here but with the straight through pipe and filters fitted someone out there must have this kind of set up and set the carbs to suit. Any advice recieved will be great, thanks for reading this post.
Keep the shiny side up and the rubber down,
Bob. 

[Bob Wessner]

I'm not familiar with your model, but are the needles adjustable for height (i.e., five notches and a clip)? If so, what position is the clip in? Have you tried raising the needles (lowering the clip)?

[M3JOC]

Hi Bob, Thanks for the reply, yes there are five grooves in the needle and the clip is set one up from the bottom, second richest position, i could move it it down one groove to the very bottom but the leanness of the burn on full throtle makes me think i really need bigger main jets, thats why i`m looking for an idea on where to start, really i was hopeing someone on this fourm would have done a similar setup before and had an idea of which mains to use. I`m sure i need to go up to at least 105 mains, but i also think that might not be enough and a 110 would be the size for me, if not bigger. It`s the straight through 4 into 1 pipe with the folded paper air filters i`m using which are causing the leaness but thats what i`ll be running it like so i have to get the mixture right.
Hopeing for an indication of which to try first just to save a bit of time and effort.
Keep the ideas comming folks all suggestions are welcome,
Cheers and beers,
Bob

[dusterdude]

oh no,two bobs

[Bob Wessner]

Yeah, and the subject is "carbs" how scary is that? 

[dusterdude]

im trying not to think about that,thank you.

[Buffo]

Mains are cheep...best to buy a few different sizes to make sure you gt the right flow rate...unless you luck out and get the right size right off the bat you are going to be buying more than one set of jets anyway and I would rather have gotten all of my jets at the same time and be done with it in as little time as possible...or you can order one size at a time and wait a week for each new size that you have to order...

[Dennis]

So the mains need changing up a bit. What size do i go for as a starting point?? I am thinking of 105 but looking at how lean it is i also think 110, do any of you guys have a best guess as to where to start .....

Looking at your comments you certainly seem to have a good handle on what you are trying to accomplish. I can't help you, never having done a 550. I do have a couple of 500's that I want to start working on, so I will be interested in your results since they have very similar carbs.

One question for you , however, don't these carbs have the so called pressed in main jets which are supposed to be NLA?

Do you have a source for them?
No secrets on this forum, Bob.        Where are you getting them?

[paulages]

this type of "press in" just means that they are the o-ring type, without threads, as opposed to the press-fit pilot jets on the '77-'78 cb550 carbs. very easy to replace.

[Dennis]

this type of "press in" just means that they are the o-ring type, without threads, as opposed to the press-fit pilot jets on the '77-'78 cb550 carbs. very easy to replace.

I know how to replace them.
What I want to know is where to get them in other than standard sizes.

Thanks
Dennis

[TwoTired]

Bike is a Honda CB550 1974, engine is sound, timing done, valve clearance`s done. now its time for the carbs, I`ve done a total rebuild cause they were full of muck, all the passageways are now clear, new air screws, new pilot jets (38) new mains(98) new needles (clip one up from the bottom), float heights set at 22mm, straight through 4 into one pipe (slashcut end pipe with no baffle) and K`n`N type filters, one per carb (069`s).

Nice description and problem statement.  Don't see that a lot. 

While I can't tell you where to get the specific jets you seek, your description does indicate the need for larger mains.  Perhaps these details will help you with a solution.
069A carbs are from an F model 75-77 and these generally run leaner than the K model 022As. While I haven't done a measurement comparison, I do know the slide needles for these carbs had a different needle taper profile than the ones for the K models.  The K needles would give you a different balance between high and low midrange mixtures than your current needles.  Yet another needle profile to consider are the ones from 627B carbs (Cb500Ks).  Again, I don't have data on the specific differences.  I just know that they ARE different.  And Cb500 carbs would run richer on a CB550 because of the difference in volumetric draw.  The K model Cb550s used 100 mains.  These may still be too small for your needs.  But, it is a significant increase.  And, you can get jet reamers and gauges to enlarge the orifice to what ever size you desire and still maintain nice round smooth holes.
http://www.cbperformance.com/catalog.asp?ProductID=525
I have heard from another who said thery found 105 mains in their Cb500.  Whether Honda put them there or not, I can't certify.

Unfortunately, the only source I know of for jets and needles is from other carbs and rebuild kits for these carbs.
Cheers,

[M3JOC]

Hi all, Thanks for the replies, well i knew i was asking a lot and i also knew the only way was trial and error. One of the reasons i wanted a starting point is because i`m going to drill the mains (in a small lathe with a pin chuck)  So i`ll start at 1mm and work up from there, will post every time i do the test and let you folks know how its going.

Two Tired- It might surprise you to know that i have a set of fully rebuilt 627B carbs from a 78 model which i have just fitted to see how they perform, same jets 38/98 same needle height. And to my surprise the bike runs exactly the same, mixture can be made nice at the first third throttle but leans out midrange and is very very lean full throttle. Results which are almost identical to the 069`s. This made me get the timing lamp out and check the advance unit but all is well there, so off with the 627B`s and on with the 069`s with mains drilled 1mm (Tomorrow that is ,Mon).
Drilling the jets at work so it`s drill fit try, next day drill fit try, and on it goes.

I am lucky in that i live on a farm estate which has a private road right outside my front door which is level for about 400yards and then quite a steep hill for 1/2 a mile, great for carb tests.

Thanks again folks, Oh jets and rebuild kits i get from your side of the pond, last set was from Z1 Enterprises, check the net.
Cheers and beers
Bob

[MetalHead550]

This may be harder to accomplish than I visualize but...It would be great for the guys who have rebuilt carbs and had to rejet due to intake/exhaust changes enter their working combinations in a post and mabey we could compile a database of sorts for rejeting these bikes.  The stock settings for various years and models should be included too.(Two Tired mabey youll get bored enough sometime)  Like this:

Year of bike.  Model of bike.  Type of carbs.  slow jet/main jet size.  Needle position.  Float hight.  Pilot screw positon.  Type of intake.  Type of exhaust

Then we could throw it in the carb FAQ to refer people to.  Ive just noticed several posts latetly where people are trying to fine tune their carbs and it would be cool to have a quick reference like that so at people could eliminate alot of guess work.  Just an idea.

[M3JOC]

This may be harder to accomplish than I visualize but...It would be great for the guys who have rebuilt carbs and had to rejet due to intake/exhaust changes enter their working combinations in a post and mabey we could compile a database of sorts for rejeting these bikes.  The stock settings for various years and models should be included too.(Two Tired mabey youll get bored enough sometime)  Like this:

Year of bike.  Model of bike.  Type of carbs.  slow jet/main jet size.  Needle position.  Float hight.  Pilot screw positon.  Type of intake.  Type of exhaust

Then we could throw it in the carb FAQ to refer people to.  Ive just noticed several posts latetly where people are trying to fine tune their carbs and it would be cool to have a quick reference like that so at people could eliminate alot of guess work.  Just an idea.

Now thats a great idea, in fact when i started browsing these fourms it was somthing like that i looked in the carb faq`s for. any data would of course only be right for that particular bike but it would give others a great starting point.
How about it guys,
CB550, 1974, 069a carbs, 40 pilot jet, 100 main jet, needle clip one down from the top, float height 22mm, pilot screw 1+3/4 turns out, Straight out the manual...
Would be a good project for someone with the knowlege, TT
Cheers,
Bob

[TwoTired]

mabey we could compile a database of sorts for rejeting these bikes.  The stock settings for various years and models should be included too.(Two Tired mabey youll get bored enough sometime)  Like this:

Year of bike.  Model of bike.  Type of carbs.  slow jet/main jet size.  Needle position.  Float hight.  Pilot screw positon.  Type of intake.  Type of exhaust

Then we could throw it in the carb FAQ to refer people to. 

Now thats a great idea, in fact when i started browsing these fourms it was somthing like that i looked in the carb faq`s for. any data would of course only be right for that particular bike but it would give others a great starting point.
How about it guys,
CB550, 1974, 069a carbs, 40 pilot jet, 100 main jet, needle clip one down from the top, float height 22mm, pilot screw 1+3/4 turns out, Straight out the manual...
Would be a good project for someone with the knowlege, TT
Cheers,
Bob

I made a chart like this a year or two ago with what I know about the American Models.  SteveD finally snatched it from one of my posts and put it in the carb FAQ.

I can update the original chart.  But, I don't know how to get updates into the FAQ.

Bob, what manual did you get your data from?  My Honda shop manual and personal collection examples differ from your data.
Cheers,

[M3JOC]

Two tired, Hey guess what, i got it wrong. Here it is right out the manual.
CB550, 1974, main jet 100, pilot jet 40, Throttle slide 2.5, Air screw 1+1/2 plus/minus3/8, float hight 22mm, jet needle setting third groove.
CB550F main jet 98, pilot jet 38, throttle slide 2.5 air screw 1+3/4 plus/minus 1/2, float height 22m, jet needle third groove.
Sorry about the confusion, the manual is a Haynes and covers
CB550 US 1973/1976
CB550F1 UK 1975/1977
CB550f US 1974/1977
CB550K US 1974.1977

Also i looked in the Faq`s and didnt see your chart, will look again.
Also, and its quite a big also, i thought the jet sizes were in fractions on a milimeter, 98 being 0.98mm, 100 being 1mm. But looking at the 98`s i have here right the hole is more than 1mm already?? Now i really am confused, and i thought i knew what i was doing.
I bought this bike altered so mabye the previous owner has enlarged the mains already cause its the original old jets i have here at the moment, please could somebody put me right here. ARE the mains in millimeters, IE is a 98 jet 0.98mm.
Thanks,
Bob

[TwoTired]

The numbers I put in the chart found in the FAQ, are numbers I gleened fro the Honda CB500/550 shop Manual.  The Carb Identifiers, I found on my collection of machines.
The Honda Motorcycle Identification Guide (published by American Honda) claims the following models were manufactured:
CB500 1971  (K0)
CB500 1972  (K1)
CB500 1973  (K2)
CB550 1974  (K0)
CB550K 1975  (K1)
CB550K 1976  (K?)  Still product code 374
CB550K 1977-78 (K3) From Honda Shop manual
CB550F 1975  (F0)
CB550F 1976  (F?)
CB550F 1977  (F2) From Honda Shop manual

I don't think these explain models or years sold outside North America, based on input received from others in these forums.

I have a Haynes Manual as well; Covers both the Cb400F and the CB550 Fours; Copyright 1976 Printed in England.  Not all the model year references jibe with the American Honda and Honda Shop Manual publications.  However, all the examples in my collection and those encountered here in California have fallen within the descriptions of the Honda publications.

It is my understanding that the jet numbers are in millimeters.  A #98 should be 0.98mm, #100 should be 1mm, etc. as you describe.  If you have a #98 with a larger hole, I suspect it's been drilled.

Cheers,

[M3JOC]

Hey Two Tired, took my mains into work today and sized them carefully with metric drill bits, and although they say 98 they have indeed been taken out to 1.03mm, So i`ll clean out another set of carbs i have here and stick them in and see how the old dog goes. I should have done this in the first place but the old carbs had lay on the bike idle for a while and the pilot circuts and jets were real bad, so i built up a set to standard as a starting point. Should have checked the size of the original mains to see what it was running, My bad, never mind we`ll see how this pans out.
Thanks all for the suggestions and help dudes,
Have a beer on me,
Bob

[M3JOC]

Ok, now we`re getting somewhere, the new o-rings arrived at work today and the main jets (103) are in a set of revamped carbs, and i`m off out to the garage to fit them.   I suspect that all will be well after this, or at least better.
Will post and let you guys know what the mixture is like after a warm up and a ride about. Which might be tomorrow as its geting dark here now.
Happy November,
Bob