idle jet differences , 069's

[K2-K6]

Could an overview be useful?

The original intake system on these it would be easy to describe as exquisitely resolved, for a 1970s engine with such smooth idle, linear response all the way to 10,000rpm without glitches and roughly 100bhp per litre,  they deserve that wording as such a finely designed and specified production ready engine.

They are veeeery sensitive to any changes in their components though, that's either the vacuum characteristics, fuel levels or ultimately jetting.

There's effectively no facility to competently alter the vacuum curve, with any shifts in carburettor feed likely to need out of range jetting compensation to get toward where Honda set them. Even the airbox lid in different specifications will shift the balance.
As you note from experience with Amal and SU (I alter vacuum gradient on SU with oil viscosity to trim above and below target for transient openings) that tool is missing here.

The compression and cylinder draw on this engine is a serious consideration as they will run quite well with very significant upper cylinder damage,  but with some odd response effects. This thread http://www.sohc.co.uk/index.php/topic,14049.0.html may give some idea if you look through at the state of the pistons when dismantled.

As already mentioned by others, current pattern brass components are often no match at all for the accuracy of the original parts. Kiehin where particularly good in production parts.

[deltarider]

One thing I noticed is a reference to a slow jet. There is'nt one on the parts diagram so presume it's a drilling. Must check that for size.

It should be in the parts diagram, part 17 in: https://www.cmsnl.com/honda-cb550f2-super-sport-550-four-1977-england_model17121/partslist/E17-1.html
Anyway, it's supposed to be a #38

[fogrider]

The reference I saw was to a slow jet, but not stated as idle jet. I assumed it was meant to be slow air jet, I've seen them quoted as 150 and 220. 220 could be for the 750's though.
No problem with the idle jets, original 38's, the long ones you illustrated . They do seem to be nearer 40 though but it idles OK at the right air screw turns out.
I checked the air entry hole which is in the air box side of the carb mouth. I assume that is what is referred to as the slow air jet. It works out as a 180, much more air than a 150. 
The original needles are now back in. The difference  in diameter at set points amounted to nearly 2 needle clip positions weaker.
The new main jets with their O rings are a firm push fit, but just in case, I shall get "proper" O rings on Monday before re-fitting the carbs. Will put the ignition back too so it's a fair comparison.
Here's hoping.

[fogrider]

Just found the reference to a slow air jet - it's in an addendum to the CB550K manual, shows a fuel level of 14.5mm so must be a different version of these carbs.
If anyone's got some 069a's accessible and can measure that small air drilling to the side of the venturi, that would be a
very useful bit of info. My guess is 1.5mm, but confirmation very welcome.
Anyone ?

[deltarider]

Just found the reference to a slow air jet - it's in an addendum to the CB550K manual, shows a fuel level of 14.5mm so must be a different version of these carbs.

That concerns the later K3 and K4 models which had totally diferent PD carbs. See pic below. Just to make sure: what type do yours have: the PD or the oldstyle?

[fogrider]

That's helpful, mine are the ones in the lower photo. Don't know what model ref . It would be great to check the size of that air drilling in the carb face before the carbs go back on again. probably correct, but  worth checking if they are part of that massive weakness bottom end.

The way it went more and more rich when well up the rev range is strange, especially with that thin foam filter in. That would normally weaken it off . I have read on here that it could  be fuel being pulled past inadequate O rings on the main jets. They are new on the aftermarket jets, I will get some better ones tomorrow even though they are are a reasonably firm push fit.

The jets do check out as 98 though.

[fogrider]

After being side-tracked by other things, finally had another run with the original needles back in. That's all the original internals now back in, clip 2, float levels correct. Ignition back to standard. Screws 1.1/2 out.
Started fine , sounded good, had to take the choke off very early (opposite to before) as it was showing very rich on the Lambda reader. Even after 10 miles it was showing way over rich the full range of throttle  and yet STILL had a small stumble just after opening up.
Back home, took the plugs out, jet black.
All I've done is put the original needles back in !
The aftermarket needles had made it vastly weak right to the middle range , then too rich top end. 
I tried some new main jet O rings, 1.2x4 (on stock, 20p for 4 ), but I'm waiting for some 1.2x4.3 which calculate as the right size (80p for 4 ). Maybe that's the top end richness issue, can but try........

[K2-K6]

Interesting there's so much difference and echoes that which most find, that current replacement are highly suspect.

Be interesting with the replacement O-rings to see if it clears out the top end jetting. 

Have you got paper filter in yet? as I'd perceive that to make difference to that just off idle characteristics of slightly lean. If it's with a new filter, then it looks like perhaps 1/4 turn in on airscrew would assist.

[fogrider]

1.2x4 should do, as the originals AND the new aftermarkets were 1x4. But, the stretch on 4 may be just a little too much and not enough crush. Cheap enough to try some 1.2x4.2.
I've tried it with and without an air filter, both paper and the foam that was in it. No difference. All I can do is try something else and see what happens. The difference on needles is incredible. I'm going to try the aftermarkets, which made it too weak bottom end, but in one clip richer. At least with the Lambda in I can see the results clearly and it stops me making wrong assumptions.
These carbs seem very sensitive to small changes, I suppose that's a product of a small choke size.
I know it's said these carbs need the original brass bits in, but I suspect there is wear in the needle jet, that would explain the issue somewhat, not entirely sure what size it should be, more research req'd. Must find Deltariders chart again.

[K2-K6]

"These carbs seem very sensitive to small changes, I suppose that's a product of a small choke size."

Looking at it logically, creating the carburettor bore size for maximum rpm of each cylinder and aiming for an ideal airspeed at that point will give a proscribed venturi size they felt was optimum.
Going to the other end of the range, at idle, then some very small metering is required to get a linear hiccup free response. Quite a balancing act, along with tiny changes shifting the AFR in fairly large percentage terms.

Always learn more about something when it's not working properly though as it makes us think harder.

[fogrider]

The compressions have been mentioned on here, finally got 'round to a check :

cold engine, 150 psi on all 4, give or take 1 psi.  Looks OK to me for a mere 9 to 1 engine.

Hopefully the 1.2x4.2   O rings will turn up today and I can put the carbs back on and try the latest  changes and adjustments. Trial and error. I think I now know what was going on, soon find out !

[K2-K6]

Compression looks pretty decent,  interesting to hear what you get when you feel you've all the obvious bugs out of it.

[fogrider]

The new aftermarket needles back in, 1 clip richer as previous runs showed the new needles made it way too weak .( much fatter profile than the originals). It's clear to me that the needle jet is worn ( it's done nearly 67,000 miles ).
Incredibly, the Lambda reader showed over-rich the entire range, right up to 70mph. I took the air filter out at the roadside, no difference, just lots of extra noise .
After suggestions on here, I had set the air screws slightly on the rich side to partly improve the pick-up off idle. Still ticked over OK.
As an experiment, I turned the screws out to 1.1/2 and had another run.  All the richness gone, right up to 65 70mph. The idle system was feeding the whole carb range, BIG style. That's a new one on me, I've had this Lambda set-up in my Austin Gipsy (Zenith), my Citroen DS (twin choke weber)  my Triumph T100 unit twin (Amal concentric ) and my Cortina estate (Ford/Weber), none of them had the idle system working the whole range. Only the bottom end.
The idle jets are stamped 38 but measure 41, next step , change the idle jets, but , for now, it's running the best so far.
Glory be.....

[philward]

Just seen this that shows jet range - may help?
https://www.caferacer.net/threads/cb500-four-4-to-1-exhaust-dilema.23465/page-3#lg=thread-23465&slide=0

[fogrider]

Thanks Phil, I had spotted that chart a week or so ago. Quite different to some I have seen, much bigger overlaps. The idle system on mine is'nt just an overlap, it's a whole range mixture feed !      Without putting the Lambda reader in I would not have seen that. I suspect that the bigger size of the idle jet in it is possibly allowing too much volume into the choke area. I'm waiting for some 35 pilots to try as a test.
I had spotted something else somewhere  regarding Keihin type 1's, an article describing how someone had worked out that going to a smaller idle jet helped the transition off idle.  I wish I could find it again. That's what I will be trying next,
although to be fair , she's running really well now with the changes I've made, clean acceleration all the way except the slightest stumble just off idle, good tickover.  Good plug colour.
All this effort has turned a very badly neglected bike into a pleasant ride.
I've learned a lot about CB550f's too !