Honda-SOHC

Yes on the 550 there is no throttle speed increase mechanism like you normally find on other carbs.

I normally use choke open to start and once running close chokes to about half way whilst it warms up. I do NOT need to keep the throttle open though whilst warming up so there is something not right with your setup. Moving the clip will not (I don't think) help as the needle position only starts to have effect at higher revs. That said I run mine in the middle position so you may want to change them ans see if it has any impact.

"I normally use choke open to start and once running close chokes to about half way whilst it warms up" - do I understand you start engine like me, e.g. w/o choke use (= choke open) and then you use it halfway? Or wise versa, meaning you engage choke fully (= flaps are fully closed, so restricting air and making mix richer)? Sorry for such question, I'm not native english speaker 

Hi Paul
thanks for reply!

Yesterday evening I opened (yes, for the first time  ) manual to my CB550K1, reading the cold start procedure. Seems I had different expectations from how starting cold engine...
but point to point answers to your post:

I am not sure what your real problem is here, you say bike wont start on choke but you are obviously able to start it, so is the issue that it is harder to start than you would expect only from cold.
Yes, I can start, but impossible without trottle opening. When I open trottle its starts well without choke, but then I need to keep trottle open till it is warm enough to keep idling itself w/o trottle. If I use choke I need to use trottle too, but it starts much harder and does not respond trottle well (too rich mix).
Normally choke should make mix richer but in my case looks too much???
Another example, after I start w/o choke, while keeping engine alive with trottle to warm it up I engage choke (even partially), RPMs goes down, engine tends to stop / runs hard (too rich symptom)

I am assuming the chokes are operating properly as Gerben has rebuilt the carbs and I am also assuming the pilot air circuits are clear and the pilot jets are clear.
Yes, I confirm chokes operates properly, all pilot circuits are clear and jets are new genuine Keihin 38

Are you using the correct starting procedure, below is what the original Honda owners manual recommends
After reading manual and your post seems not really 

COLD ENGINE STARTING
PROCEDURE
...
4) Position the choke lever to the full closed position. Yes
5) Twist the throttle grip inward slightly and depress the starter button. I did not do this as part of procedure, but finally was doing so as the only way to start 
Honestly, I expected I should only use choke and engine will run on higher RPMs, like my CB750 K7....
6) After the engine starts, operate at approximately 2,000 rpm until the engine will properly respond to the throttle with the choke open. Does this means I need to keep trottle open for some time to make engine warmer? But this can be quite some time... strange to me, I really expected that no trottle needed to warm-up using choke. This is not really very user friendly

You also say that when warm it runs and idles well which would seem to indicate that the idle circuits and pilot jets etc in the carbs are all OK. Exactly. BUT, when riding it, I feel that when trying to accerate from lower RPMs, engine suffers from too rich mix till it reaches higher RPMs.


Here is my recommendation

1) Make sure there are no air leaks at the carb to head rubber joints Rubber joints looks good and tight, I don't know how to test better. But if they would not be tight, mix should be leaner, which is not my case
2) Are you sure you dont have a restriction in the fuel lines ( I had a strange problem with my old petcock that was strangling the fuel flow). I found this because if i turned the fuel on and then left the bike for 5 minutes this gave time to fill the float bowls and starting was much easier. Have you tried just  directly connecting an external auxiliary fuel tank to eliminate any such issues Yes, I'm sure there is nothing blocking. Petcock is new (Honda), new hoses...
3) May be worth changing points and condensors I will, but normally this does not explain my symphoms
4) Try another set of coils if you are using the original ones Don't have spare set, but again I don't think this can cause my issue
5) You said you used a 38 pilot jet but I thought the right one was 40 (that said I have 627 carbs) According to specs, 022A, model year 1975 shall have 38
6) Make sure this is not an ignition problem rather than a carb problem
[/quote] as points 3&4 above

All in all, it still looks to me choke is completely useles (maybe can help in really cold weather?)
Are there any other carbs on later 550s that are better for cold start? (550F?)

Another 2 questions:
- what's the length of fuel hoses from carbs to cock?
- is it possible to replace hoses (installation especially) provided I use genuine Honda (got from 4into1 declared as genuine) without separating carbs from stay plate?

Starting new thread as it seems I will have more questions. Sorry for them, going to "play" with carb for the first time..
Appologize if this has been answered elsewhere many times already

So let's start:
- is it possible to check and change needle settings (to see which notch is used) without complete disassembly? I'm afraid answer is no, but just in case
- on my carb set, after I removed main jets and turned carbs over emulsification tube dropped out just by gravity.. Just on 1st carb. Tube is very loose in rge hole.. Is that ok? No impact on carb function?
- mixture screw - I suppose it changes air flow, correct? So turning in makes mix richer?

Thanks guys!

So, with regards to viton O-rings, I need to know sizes and qty used...

I've seen it some time ago on the forum (here or us) but cannot find it now..

I need this for CB550K1 (carbs 022A) and also for my CB750K7 (PD41A carbs)

Thanks!

Good news it’s running beautifully, no crackles and pops on the overrun, pulls smoothly through the range, the No1&4 plugs are tan centre dark grey outer, I’ll have a look at 2&3 when I can be bothered with the faf of taking them out but I expect them to be the same from the way it’s running, old pilots pulled out easily with just pliers, tapped new ones gently in with a flat face drift, old pilots were 35’s they were dirty and partially blocked, bright new 40’s fixed the lean bottom end, I very carefully set the floats to 12.5mm then attached a remote fuel tank with the carbs supported level on my BD workmate, I checked the actual levels using a clear plastic tube on the drains, 2,3,4 were fine with the level of fuel in the tube coinciding with the bowl gasket but No1 was about 5mm high so I readjusted the float height in No1 and got the actual level to match the other 3, I guess there may have been a slight bend in the float support arms but they all looked straight, anyway nice now, noticed the brakes weren’t as good as I remembered so bled them, left was fine but got air and dark fluid from the right, brakes are now very good again, all in all a good day in the garage!

Where did you source new pilots 40?

My experience generally:

- USA import has identification label in steering head (right side), including mfg date, while European ones does have them on right side of the frame, next to side cover
- US import shall have stock high bars


I strogly recommend to study this site, there are all small importnat details to see if bike is stock/genuine or not. But, there are US models only

http://honda750expert.com/

I'm very sorry if I missed some important info, how can I make donation? I went through this thread but did not find relevant info...