Post by: Towsejames on April 13, 2026, 07:54:33 PM
I recently got a set of Keihin 069A carburettors in rough shape and plan to clean them up an run them with pod filters on my 1976 cb550f bitser.
I’ve had a look at all the vital rebuild parts and they all seem like they should clean up and be functional
except for the small cap that is missing in the photos. Please see attached.
My question is, does anyone know where I can find a replacement cap, plug or whatever its name is. And if left like this would this cause an air leak?
These are located on the end of the shaft that operates the slide at the top of the carb.
Thanks for any advice
James
(https://uploads.tapatalk-cdn.com/20260413/80f3b9444f8a8d52d0150bfbc21ad5d1.jpg)
(https://uploads.tapatalk-cdn.com/20260413/210237c3ef259eae6c17f8770c60112b.jpg)
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Post by: exvalvesetdabbler on April 13, 2026, 09:08:14 PM
If you do as search for core plug in the size needed you might get lucky. On the 400/4 they're 13 mm.
Regards
Dave
Post by: Bryanj on April 13, 2026, 09:28:40 PM
Post by: DomP on April 13, 2026, 10:15:35 PM
Post by: Towsejames on April 13, 2026, 10:47:30 PM
As for the pod filters, they seem difficult to find any decent set up. I’m sure it’s just a case of measuring for the correct size and jetting accordingly? If not the standard box will be going back on
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Post by: Bryanj on April 14, 2026, 05:27:22 AM
Post by: andy120t on April 14, 2026, 07:53:40 AM
If you want the bike to run well/at all/ not spend months tearing your hair out and still not having it run properly:
1. Throw away those carbs
2. Find the other type of carbs ( what are the ones that are easier?)
3. Use the standard airbox and filter
4. Get riding not cursing
4. If you still want to use pods, at least those carbs aren't quite such a pain as the Keihan ones
Did I capture that correctly?
Post by: Bryanj on April 14, 2026, 08:40:56 AM
Post by: Oddjob on April 14, 2026, 10:01:32 AM
The bikes run better with the standard air box and filter, you can fit pods but it’s a trial and error system after to get them to perform right. Most give up after a while.
That’s about it. You were almost right
Post by: K2-K6 on April 14, 2026, 10:49:56 AM
Thanks for the advice and the info on the core plug, I’ll have a measure and see what I can find.
As for the pod filters, they seem difficult to find any decent set up. I’m sure it’s just a case of measuring for the correct size and jetting accordingly? If not the standard box will be going back on
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Its commonly given (in mists of time & currently extrapolated) that running less restriction on intake side of carbs gives more fuel demand, then following a path to do that, often to bring something unsatisfactory and more mysterious in effect.
Reality is that it drops the vacuum the carb is subjected to, that causing it to pull less fuel for exactly the same combustion demand, resulting in flat spot bogged response.
Normally, the advice gives larger main jets etc to start, which rarely corrects but usually dumps too much fuel at different ratio that may cover some discrepancy, but just adds to confused interpretation.
I'd start with larger pilot jets, by two steps if available. That will also need bespoke setting of airscrew adjustment to optimise the idle running. This will then mainly correct the critical transition fuelling going toward getting into main jet territory. These idle circuit have some considerable influence over the fuelling curve, more than is generally acknowledged. They also have to be thoroughly verified as clean, scrupulously.
The original ignition is a very good design in my view, and works really well in practice. There's limit in currently available parts that can compromise it though, and advantage available (particularly with this carb setup) in using a good electronic system.
The Boyer system offers much thats desirable, over and above std. Notably it keeps the same dwell (saturation time of coils) for all rpm, which should help here. Also a more easily obtained parity between 1&4 ~ 2&3 cylinder firing discrepancy.
Also try resistance on both plugs and caps, accompanied by the absolute minimum plug gap that's recommended by Honda for the engine.
That should give a decent baseline setting to then evaluate and consider if it's effective or bring points to think about changing.
Post by: Towsejames on April 15, 2026, 11:11:14 AM
No Andy. The 500/550F used the type shown in the pictures, both were Keihin type and were either 623b or 069a as a rule in the UK. It’s when the 550k3 enters the picture that things start to complicate. That used PD carbs and these whilst actually being a better carb caused problems. They block up easily when stood for a while. Used every day they’d be ok. So most times the advice for those owners is to change to the earlier 623/069 type. It does involve changing the manifolds at the same time however.Thanks for the reply.
The bikes run better with the standard air box and filter, you can fit pods but it’s a trial and error system after to get them to perform right. Most give up after a while.
That’s about it. You were almost right
I’m actually in the middle of doing exactly this. The bike came with a set of PD carbs fitted. They need cleaning. I’m cleaning up this set of 069A to replace them as I heard they are less troublesome and I prefer where the choke is operated from.
The 069A have 110 main jets fitted, I haven’t checked the pilot jet yet. I’ll be running the standard airbox (for now) and a laser 4to1 exhaust. I’ll see how it runs like this and potentially mess about with the jet sizes if needed.
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Post by: Towsejames on April 17, 2026, 07:51:05 PM
I have 110 main jets and 38 pilot. Does this sound like a good starting point. I think I’ve heard that standard jetting is 100/40.
I’m missing an idle mixture screw and x1 pilot jet for whatever reason.
Disclaimer I did actually order a cheap eBay kit but the brass parts are all wrong. Anybody know of any good ones before I buy the Japanese kits?
Thanks
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Post by: Nurse Julie on April 17, 2026, 08:36:09 PM
Post by: Oddjob on April 17, 2026, 08:47:50 PM
Post by: DomP on April 17, 2026, 11:35:29 PM
Post by: Murf on April 17, 2026, 11:37:37 PM
I would say it sounds like a starting point, if that’s what you have see how it runs on it, the final set up you are aiming for will make a difference i.e air filter type (standard or pods), exhaust type (standard type or aftermarket), but you have to start somewhere. The Honda booklet about carbs in Ash’s drop box or Aladdins cave has some great info in it.
Post by: Towsejames on April 18, 2026, 12:47:50 AM
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Post by: DomP on April 18, 2026, 09:02:08 PM
Post by: Towsejames on April 19, 2026, 09:21:13 PM
Parts ordered from Nurse Julie for the 069A carbs. I can’t wait to see what it’s like on the other set once gone through properly.
Thanks for your help guys.
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Post by: Seabeowner on April 20, 2026, 07:19:07 PM
Post by: 3scs on April 20, 2026, 07:20:46 PM