Topic: cb550 carbs: what exactly should i expect out of a 30 year old machine?

[paulages]

I've been tweaking my carbs, and though it's running pretty damn well, it certainly still has it's moments. i went searching through the FAQ's and I've watched many a thread talking about fine tuning carbs in non-stock form, but I've finally come to the realization that i don't know what is normal. am i expecting more than i can get?

one guy in my crew has a stock cb550K... 069 carbs and the stock airbox, and stock 4 into 4's. this is all i have as a reference, as the only bikes i have ever consistently ridden were several cb or cl350's with CV cabs, or my '79 cb750 DOHC with an accelerator pump. there is another 550K in the fleet, but it has aftermarket 4-1's on it.

mine is a '76 cb550F, with pods (never had the airbox when i bought it), and a custom silencer (that was missing too) on the stock headers. the silencer is pretty restrictive for being a glasspack, as it is nothing more than a slip in baffle in a 1.5" pipe coming off of the header. nevertheless, it acts much like a glasspack...surprisingly quiet at idle, but opens up a bit in the higher RPM's. currently i have stock pilot jets, and 110 mains, with the needle raised one notch from stock. i only changed the needle a few weeks ago, but i can't really tell if it's for the better or worse. the plugs still read the same.  also,  i'm running a Dyna-S, by the way.

so...my plug chops come up surprisingly perfect, but it still acts weird sometimes. i have believed it to be a fuel flow problem, starving the carbs at higher RPM's, but i came to wonder if i wasn't expecting something out of them that they couldn't do.

1) WOT:    if i lay on the throttle from a lower RPM,  it doesn't hesitate, it bogs. if i climb more sensibly to that higher throttle range, it performs fine. however, if I'm at say 6-7K RPM and decelerate for more that a couple of seconds, it coughs a tiny bit before responding quite well again. am i just expecting what a CV carb or acc. pump would do?

2) IDLE:     i can never start it with the choke all the way on. if it's cool outside, it likes the choke at about 3/4 throttle for about a minute. i usually just bump up the idle speed for the first few minutes, with no choke at all. it idles very smooth, but occasionally after a bit of riding, usually at highway speed, it will sound a bit "wheezier" than usually at take off, almost as if the carbs were suddenly out of sync. it actually feels like a couple of them are gasping, while the others are drinking. i know it could be the "pod turbulence" problem people talk about, but it seems totally random, which makes me suspect fuel flow again.

3) MIDRANGE:  holy #$%*, do the 550's love the midrange. can't complain much between 3K and 7K, other than the occasional post-decel hiccuping i mentioned in the 3/4 and greater range.



yeah, i know that's a lot of info...any thoughts?

[TwoTired]

one guy in my crew has a stock cb550K... 069 carbs and the stock airbox, and stock 4 into 4's

069A carbs are from an F model.  38 slows, 98 mains and a needle profile tailored to the 4 into 1 with a stock muffler.  Unless the innards of the carbs have been changed,  I'm guessing his bike runs pretty lean.  At least, in some throttle positions.

You did fail to mention details about your carb's guts and settings.
What is your Idle screw setting?   Do you have the 069A carbs?
Slide needle from what set?
Emulsion tubes from?
Float level setting?
Slow jet size?

Spark plug numbers?

The stock bike will accept 1/2 -2/3 throttle without the wheeze.  Beyond that and the throat vacuum drops too much to draw adequate fuel from the jets or emulsion tube.  The stock filter restriction lessens the vacuum drop extreme.

Possibly having more fuel in the emulsion tubes can help with enrichment with throttle opening, read higher float level.  Also, having more fuel and air available in the slow circuit can help, too;  bigger slows and more open idle screws.

I don't know why you think you need such large main jets.  Did you change the cam, or port the head?  Are you operating beyond red line?  Have you tried 100s?  Did WOT plug chops make them white?  Maybe your main is okay but you need a different needle profile from one of the other carb setups?

You do know that changing, say, the float setting, may improve your low throttle response.  But, then you could require a change to main jet or needle profile to lean the upper throttle settings.  Many of the adjustment tweaks are interactive.

Cheers,

P.S. One more comment.  Race bikes are often tuned or configured to do one thing well.  Street bikes are tuned to operate in a wide variety of situations and conditions.  Often, when a machine is purpose built, it loses some versatility.  I guess that's my dissapointment with cafe style bikes.  When you modify them to look like race bikes, they are often no longer docile and responsive street machines.  It takes a lot of work and a bit of compromise to have a large performance envelope.

[paulages]

thanks TT, i was hoping you'd chime in. yeah, i agree with what you are saying about cafe bikes and their fallbacks. i am gearing towards low end city driving power and willing to accept a loss at cruising speeds. i tried to include everything i could think of, but i guess i was caught up in telling it all. here are the details for now:

-stock 069A carbs
-stock emulsion tubes
-stock needles (the keyster kit's needles were quite different, and i wasn't that ready to tamper with honda's engineering quite yet without a good reason), one clip richer from stock (2nd from bottom instead of third, if i remember right)
-stock slow jets (038)
-110 main jets
-ngk 7 plugs, i think. i'll have to double check.

honestly i can't remember for sure if i have 110's in there or not...i had someone recommend them with the pods, and i thought i tried it as a starting gamble. i still have the 98's, and i found a set of 105's that i ordered from the guy who made the recommendation. maybe i'm remembering wrong and i actually put 100's in there as a starting point. seems like the keyster kits came with 100's...the choke thing throws me though, because everything else indicates lean, if anything. i'll come back with that answer soon. oh yeah, i went up a few thousand feet to mt. hood, and i was blowing a bit of grey smoke and running worse, which i interpreted as richening out even more...but as i said everything else indicates lean including nice chocolate colored plugs, MAYBE on the tan side.

the float height is a good idea. brad (southbound) was blowing tons of smoke, and i turned out to be a sticking float. goes to show how big of a difference float height can make.

[dusterdude]

paul,your wot or highway issues are probably an airflow problem that pods seem to have at higher speeds,mine do the same thing.

[StevieMac]

paul,your wot or highway issues are probably an airflow problem that pods seem to have at higher speeds,mine do the same thing.

That's a good point.  I run pods on my 750 chop and have experienced that as well.  If you move your legs to block the pods from the side wind it will run better.  Cross winds are of course especially bad.

[dusterdude]

xactly,i get a lean "swoon" at 65 or so mph,i can put my girlfriend on the back and that takes care of that problem.

[paulages]

i pretty much ride with my legs right accross the side of the pods, so no luck there. like i said, it's inconsistent.took a ride the other day  on some local windies, running 7k-10k most of the way. the entire ride, it ran like a top. low end, mid-range, top end...then yesterday coming home from work on a 35 mph zone most of the way (and traffic pretty much kept me there) it started doing the wheezy idle again when i got into downtown stop/starts. no special turbulence and not over 55 much at all.   

[78_SaltLick]

have you noticed if it gets worse when its hot outside?

[paulages]

no. starts easier, but that's all. sometimes seems related to engine temp., which would indicate lean conditions though.

[TwoTired]

Contradictory info

i wasn't that ready to tamper with honda's engineering quite yet without a good reason

Yet you changed the needle clip and the main jet.  That was Honda engineering, too!

The F model clip position was 2nd groove from the top.  So, you went two steps richer on the throttle valves.

You still haven't mentioned your idle screw setting.  Here's why I want that info...

10 or 15 years ago, I bought a new gadget; an exhaust gas analyzer.  I did a tune up to the 550 and at the end of it stuffed the analyzer up the exhaust to measure hydrocarbons.  Then I adjusted the idle screws for lowest levels at idle.  Purred like a happy kitten on the centerstand.  But, I wondered why all the idle screws were at now at 5 turns out.  How could the manual setting be off so far?
The test run gave the immediate answer.  Throttle changes more than 1/8 turn just made the engine wheeze when under any load.  I didn't get 50 feet, before heading back to the garage for a screwdriver.  I proceeded to turn each screw back in, in half turn increments, and then driving a few feet for effect.  Response improved steadily, and when it got close to it's old self I changed to 1/4 turn increments,  and then 1/8 turn increments. This process repeated until I had the throttle response I was used to having with the bike, and an additional 1/8 turn made no response improvement.  Turned them back out 1/8 turn for a "peak" setting.  Back to the garage I wondered what the optimal setting ended up being.  Counting turns I found them all to be at 1 and 1/2 turns.  I checked the book spec. again; 1 1/2 turns.
Who could have guessed that Honda knew how to adjust their bike?
This 74 CB550 is has the stock 4 into 4 and airbox.  However, I do have A Uni oiled foam filter instead of the stock paper type.

Maybe, just maybe, your exhaust and filter changes require you to find a new idle air bleed setting?

Plug color:
To my mind, light tan is is where you want to be.  Chocolate, while yummy, is in the too rich range.
Missing from your description is if that is a general color, or a fixed throttle position plug chop result.
( You could, in theory, have a rich slow and wot setting, and a lean midrange setting, or other combinations, to average chocolate brown plug deposits.)

Low speed throttle response:
I don't think you should ever be able to snap the throttle open from idle, without the wheeze response.  1/2 to maybe 2/3 yeah. (No accelerator pump and no CV).  You'll be slobbery rich if so.

The physics of the slow jet orifice is tied to barometric pressure difference between carb throat and surrounding atmospheric pressure.
 The filter material before the carb inlet effects that pressure differential.  Materials that allow high flow at high inlet speeds, offer little resistance to flow at low speed as well.  And, this creates less of a pressure differential in the carb throat at low and idle speeds when compared to surrounding atmospheric pressure.  This means a 38 slow will supply less fuel with low restriction filtration, even though at 1000 RPM the engine requires exactly the same volume of air to sustain that engine speed.  The air bleed screw should be able to adjust the mixture ratio correctly, but the total volume supplied may not be enough when the slide is opened and the throat baro pressure raises significantly.  Think accelerator pump simulation.  I'm thinking that your bike with pods probably ought to have larger slow jet orifices.  Find some 40's or 42's, perhaps, then retune your air screws for mixture and throttle response from low RPM.

i am gearing towards low end city driving power and willing to accept a loss at cruising speeds

It seems odd that you chose pods, then.  Pods are for breathing at high RPM.  Seems like you've chosen the wrong tool for the job.  The assemblage of components is the result of design trade offs toward a specific goal.  There are few components that do all things for all functions and conditions.

Lastly, your "stumble-wheezy-intermittant" problem.  Start tracking the local Barometric pressure, to see if there is synchronization with the intermitantness along with engine or air temps.

You did ask for "thoughts", yes?

Cheers,

[paulages]

TT- i didn't change the needle clip position until after i had determined that i seemed to be running slightly lean in accompanying throttle range. i said this fact in my first post. sorry i forgot to list my idle screw position...they're set at 1 1/2 turns out. also, when i did my plug chops, yes i did them at specific throttle ranges. describing plug colors in text is a bit hard, but chocolate is perhaps wrongly describing them. you know the color spark plug references in some repair manuals? mine were the picture of a perfect plug exactly.

i set these carbs up exactly stock, except for the mains, and this was because at the time i had no stock airbox to work with, and took someone else's advice as to what pods would do to WOT airflow. look, i know you're a pretty staunch "stock guy", and i really do agree with your reasons. honda engineers knew what they were doing (i read your idle test anecdote in an old thread, by the way). but sometimes, we end up with reasons to have to experiment and work with what we have. some of those may be aesthetic (many people think pods look great, and i'm inclined to agree), and some may be due to a lack of original parts (where i was at). i realize the downfalls of pods, and i realize the great benefits of hondas original engineering. just because i apply for help on this board doesn't mean i'm a total bumbling fool. i figure if you're going to have to change anything, at least start from the best known arrangement, which i did except for the mains. in any case, i realize that despite your joy of pointing out where others have fallen from grace with stock arrangements  , you are really quite helpful and i appreciate it.

here's another way of describing the wheeziness i get. when the engine is running normally and in neutral, i can snap the throttle from idle, not to WOT mind you, and i peppily responds (with the usual honda sucking sound). when i gets the wheeziness, it usually seems to be running too hot and sounds like it is gasping when i do the same little rev from idle. during the same conditions is when it usually gets the decel hiccup, where it stumbles for just a second when i give it throttle again after a couple of seconds of engine braking. i figure hot probably means lean, but i haven't pulled the plugs yet when it is doing this. (i know: do that)

 i will double check what size mains i have in there, and verify what position i have the clip in. i set it up to what i believe was stock before i richened the needles a notch, but it's possible i was acting on incorrect information. and i will try fiddling with the bleed screws.

[TwoTired]

Contrary to what some other unreliable persons have stated about my "position", I am not a stock bike purist.
I do not care what is done to a bike as long as it "works" as well or better than the stock configuration.
What "works" covers many levels of functionality and acceptable behavior.
One definition is getting the bike to the 1/4 mile trap signals in the shortest amount of time.
(That's great.  But, a street bike needs to do more than that.)
Another definition is being able operate around the block for the first time. 
(A good start. But, I'm a bit more demanding than that.)
I happen to like Honda's definition of a well mannered street machine under a wide range of operating conditions.  Having driven stock and modified bikes, I can tell you that the path to a well mannered street machine is shortest by putting it in stock configuration.  A modified bike can be made well mannered.  But, it takes a lot of work to make balanced performance.

Here is an example:
The 76 CB550s were available in both K models and F models.  Engines, induction, gearing were all identical.  But, the exhaust, and only the exhaust was different between these two models with respect to engine performance.  With that singular change, here is a list of known carb component changes regarding carb set up.
- Slide Needle profile.
- Slide needle position
- Emulsion tube air bleed holes sizes.
- Main jet size
- Idle air bleed screw tip design and setting.

This tells me that if you simply change exhaust restriction, you have to re-examine each of the above variables to restore the wide range throttle response and engine run function across the operating range to the level that Honda engineers created with their engineering  dollars, dyno, instrumentation, a warehouse full of parts to try out, and support from their carburetor vendor's engineers.
Want to make it even more challenging?  Let's change the induction path and the filtration media, too!  So, all the carb throat pressures are different from baseline, as well.
As an engineer who loves to tinker around with machines, this is kinda fun. (But, not on my way to work in traffic.)
For someone who just wants a good dependable bike to ride with confidence, it's a nightmare.  Particularly, if you don't know what part of the carburetor does what and when, and how the parts interact with each other.
For these people, stock is my recommendation.

For the latent engineers or engineer wanna be's.  (Nothing wrong with that.)  Adoption of a plan, gaining knowledge about the subject, learning how to experiment and correctly interpret test results, and (most important) patience with the machine in question, (it'll be ready when it's ready) can, indeed net a streetable, road worthy bike that is even more fun to ride than a stocker.  Most likely you'll learn a good bit along the way, too.

Far too many posts on this forum are more for cosmetic changes that make the bike "look" like it has performance improvements made to it rather than actual performance improvements.  The whole cafe racer "look" has many bikes falling victim to this.  To me, much of it is like getting a Harley cause all the cool guys have one, too.  (I've never been much of a trend follower.)

I've seen pics and the progress you've made to your bike.  You're clearly talented and what you've created is quite impressive.  I'm not so sure I'd want to ride it farther than around the block, as it hardly looks comfortable.  But, I want you to succeed with what you like, and that's part of the reason I've been trying to help you.  But, tuning carbs is NOT like making indentations on the side of a gas tank.  Assembling, parts is only one phase of the project.  Tuning the parts to work well together can take far longer.
I remember you saying earlier in the project, that you were going "take your chances" on pods.  I have to wonder if you still feel lucky, now?  And, are you prepared to spend more time testing and sorting out your carb issues now?  I hope you will.  But, without a dyno and instrumentation, I fear you're looking at lot's of fit and try. 

About those idle screws.  What I left out of my boring and repetitive tuning story was that on the centerstand, throttle response was quite good even with the screws back out a good deal.  But, loaded engine performance was dismal.  It's good to realize that engine mixture requirements vary with the load placed on the engine at all throttle position.  This is where dyno, test track, or steep hill can really benefit and accelerate carb tuning efforts.

Perhaps the fact is that I've "helped" all I can.  And, now, those that have been more successful and happy with pods and quick tuning can guide you to a speedier and more satisfying conclusion to your endeavor.  Fine tuning a bike over the internet is, perhaps, beyond my capabilities.

Best of luck, Paul ! 

[paulages]

i smell what you're stepping in, lloyd. i'm just busting your balls. i appreciate all the help you've given, and yes i am a bit of a masochistic experimantalist. i don't have an engineering degree, but i do have decent reasoning skills. i'm also not a mindless fanatic about anything. riding for me is only half transportation and the other half (at least) is hobby. that includes, for certain, making a bike look the way i want. that's not the same thing as buying a harley because that's what cool. as a matter of fact, none of my friends have been too particularly keen on the particular style i like. you like what you like, no? so eventually that leads you to either finding the perfect bike someone else built, or customizing yours to how you like. i want a sensible ride, so i'm not doing any ridiculous modifications like a front end that sticks out 8 feet and won't turn. yes, the jury is still out on the pods. i'm perfectly willing to give up on something that doesn't work, but at the same time not willing to give up without trying. and yeah, body work and mechanical work are different worlds. personally, i don't want to just get from stoplight to stoplight as quickly as possible. i want to have fun while riding, period.

in any case, i don't think you've neccesarily "helped me all you can." i haven't expected anyone to tell me how to set up my carbs over an internet forum. i know what work i have in store for me. all i asked, was "what is normal?" thanks for your input.

had a lot of fun riding today. 

[paulages]

took the carbs apart today, and now the reassembly of the carbs the first time came back to me. the guy i bought the pods from insisted that i should start with a 110 main when rejetting. i thought this was a bit drastic, so i ordered some 105's from him because they were cheap enough. when i rebuilt the carbs, i installed the 100 mains that came in the kit, which is what i've been running. see, my logic from the beginning was pretty much as i stated: start with the known, and modify as necessary from there. 100's weren't stock, i know, but everything i had read on here and elsewhere was telling me i would run leaner with pods, and my 98's were trashed.

lloyd---you know, i almost take offense to your comments about cafe racers and the senselessness of them and so forth, except that i know that noone sits on the computer everyday responding to frustrated bike owners without genuinely good intentions. however, believe it or not i know that tuning a bike is "not like making indentations in the side of a gas tank." body work is new to me. i did however go to school for automotive technology and used to be an auto mechanic and, though i'm no expert, am not a total idiot when it comes to the mechanical side of things. there's really no need for subtle condescention.

anyway, if you like something, you like it. it's absurd to claim that someone who likes cafe racers is any more "trend following" than someone who like a stocker, and guys who buy some glittery harley off of the showroom floor are hardly the same as anyone who actually works on keeping a 30+ year old bike alive. and even if they are? who cares?

[edit: besides, wasn't honda just following the styling trends of the british bikes of the day? if you love a production style of bike (in this case the sohc4 hondas), you inevitably are following some trend, as the market of the day dictates.]

i think my bike is surprisingly comfortable, and handles better than any of the stockers in the fleet. does it run perfectly yet? no. but i enjoy the tweaking. again, thanks for your help.

[TwoTired]

lloyd---you know, i almost take offense to your comments about cafe racers and the senselessness of them and so forth, except that i know that noone sits on the computer everyday responding to frustrated bike owners without genuinely good intentions. however, believe it or not i know that tuning a bike is "not like making indentations in the side of a gas tank." body work is new to me. i did however go to school for automotive technology and used to be an auto mechanic and, though i'm no expert, am not a total idiot when it comes to the mechanical side of things. there's really no need for subtle condescention.

There was never any condescension intended from me.  And, I never intended to offend you. The "not like making indentations in the side of a gas tank" statement was merely to point out that a different non-visual discipline was required to solve the mixture problem.  Shaping steel involves visual and tactile skills.  Correcting mixture issues is more cerebral.  Unless you have full instrumentation to relay combustion status in visual form, the bike's visual clues are more subtle to observe.  The philosophy I use is that if you understand how something works, the modifications you make bring expected and desired results in a timely fashion.  Another method is simply fitting different parts inside the carbs until it behaves to your satisfaction, without ever knowing why the parts you fitted behaved the way they do.

I believe the Cafe style began with bikes that did perform well.  But, I do not believe every bike that looks like a cafe racer performs well or even as well as a stocker in good tune.  Any modification genre will have a range of bad to good success examples.  Copying the "look" does not guarantee performance.  The form follows function, not the reverse.  That's how the genre started.

How many posts have you read on this forum about a new bike owner wanting to convert to cafe style with pods and exhaust mods.  And, the very next question is what jetting to use for his unique combination?  Or, a follow up post about, flat spots, idle issues, fouled plugs, or poor throttle response, because they got rid of that stock junk and put racer looking bits in its place.  They don't even know they tampered with the tuning and are praying someone will bail them out cheaply.  For the most part, these people aren't idiots, they are simply ignorant about the facts in this area.

(sigh) Now, I'm probably going to piss you off again, given past post sensitivity.
I've been a mechanic and an engineer.  I've known mechanics who had engineering skills.  I've known engineers who have had mechanic skills.  However, the two disciplines are hardly coincident.  Most of the engineers I've met were horrible mechanics.  Some even admitted it.  Most of the mechanics I've met were horrible engineers.  However, few of them will admit it.  In fact, they generally think they are better engineers than the ones who designed the equipment they merely change parts on. (And complain about how poorly engineered they were.)  There are good and bad engineers, like there are good and bad mechanics, and all of them can make mistakes.
Repairing a bike requires a skilled mechanic.  Redesigning a bike takes at least some engineering skills.  The more radical the modifications, the deeper into engineering you'll need to get.

 I don't know what was taught in the "school for automotive technology".  But, the typical auto mechanic knows enough to change a part, sometimes even the correct one.  And, would be totally unprepared to build a single carburetor from scratch.  Then there is the HUGE step of building 10,000 of them and having each and every one work in the designated application, while being built by people who can usually manage to put screw A into hole B without breaking it off (very low skilled, cheap labor).

I never meant to imply you were an idiot.  And, I don't see anywhere in my posts where I did.  Your bike's pictures demonstrate some pretty good mechanic skills.  But, re-tuning carbs is closer to an engineering skill than it is a mechanic's skill.  And, that is where I thought you were asking for help.  Forgive me if I got that wrong.  I'll try not to bother you again.

Best regards,

[paulages]

i'm glad you didn't get too offended, lloyd. i didn't either. i said almost offended.

actually, i think many trained mechanics are idiots. the school i went to did focus quite a bit on the theory whatever particular system was being studied. for the less cerebrally-inclined this would end up noowhere, but for a reasoning mind, this explained how power is transmitted through the gearbox; how you can get 150 HP out of some fuel and air and bunch of steel. this translates to troubleshooting potential, which is what i feel bridges the gap between the engineer and the mechanic. gotta understand what's going on before you can diagnose it.

even if the starting point was a slight gamble (one small step up in main jets), my testing beyond that has been methodical. i know i have no easy answers ahead of me, and i'm quite willing to admit when i'm wrong. if i had 98 mains and a stock airbox to try, i'd go back there and see what happens, but i don't. more plug chopping to do today.

which leads me to another thread...