After the Air Clearner its now the carbs - should I re-build

[keithtraffic]

So, managed to eventually remove the air cleaner (earlier post) and after a big struggle actually get the carbs off the bike! They are (as referred to in several other posts) the 'dreaded' PD types (PD 46A).

The original problem was that the carbs were leaking significantly from around the bowl seal and having removed the carbs and set them up on the bench, connected to the tank, I have confirmed this is definitely where the fuel is leaking from.

Having removed the bowls it looks like perhaps the last time somebody did take them apart the seals were not replaced - they looked pretty deformed and in a bad state - also the screws holding the bowls to the main carb bodies were not really done up very tightly - I was expecting a bit of a struggle here but they came undone with very little effort so I am wondering if this 'lack of tightness'  was contributing tot the problem?

In preparation I have already purchase new 'packing' kits for the carbs but here is the first problem - the top gasket in the kit has locating holes in a different arrangement to that which is on the bike (see below). Now the kit was supplied by David Silver as a substitution, so that might be the explanation but has anyone else seen this problem before?

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But now the BIG QUESTION - as the carbs are off the bike should I go for a complete rebuild at this stage or let sleeping dogs lie and just replace the bowl seals?

If the general recommendation is to go the whole way are there any good articles on how to do this - I have found one from the "Vintage Bike Builder" website which looks pretty good but wondered in there were others which I could refer to. I have noticed that both the Haynes Manual and the Honda Workshop Manual I have don't seem to actually cover the PD carbs!. Also is there a recommended kit of parts including all the jets etc - looking on this forum there does seem to have been problems with different jets being supplied which are not always correct!

Any advice on this would be welcome!

[Johnwebley]

I don't know the PD carbs. But have a good look at things like the
Float needles. See if there is a wear ridge.
Also the needle in the slide.does that have wear marks.

Remove all jets and adjustable air screws. Clean thoroughly with spirit.
Fit new float bowl seals and with luck. It should be ok.

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[simonc]

Also dont know pd carbs so cannot comment on gaskets sorry. but clean clean clean/ check float heights/ 

[keithtraffic]

David Silver have been helpful (as usual) and offered an original gasket kit which looks like it will fit. But they also offer a complete re-build kit for not much more money.

Does anyone have experience of these (Carbs are PD46A)?

https://www.davidsilverspares.co.uk/parts/by-part-number/partnumber_PCRKCB550K3/

[bruxby-clive]

I can't comment on your carbs, but the part number of the complete kit would suggest that it is a Keyster repair kit, I bought 4 of these for my CB500 K2 from Silvers and they worked first time, I have also used them on my KH250 and a Cb175, I like them, but plenty of people don't. My KH carbs eventually had to be cleaned 3 times each in my small ultrasonic cleaner, finally at a temperature of over 80 degrees C for around an hour each. I think people blame the repair kits when it is blocked airways in the carb that is causing the problem. Good luck whichever way you decide to proceed.

[andy_c101]

Hi Keith,
It was a few years ago that I stripped, cleaned and rebuilt my PD carbs on my 550k3.
I recommend new gaskets for the float bowls, deffo.
I've not seen that top gasket issue with holes out of place. You may be able to punch out a new hole; and leaving the odd hole redundant (but you can judge that easily by removing a top cap to inspect the ports).

Just to share my experience with PD carbs....
I thought/hoped a thoroughly good clean would do the trick.
But alas, I could NEVER achieve a steady tick-over and always ran VERY lean.
To cut a long story short.....
I bought & fitted new Float Needle Valves,
I set Float Height to 14.5mm (both of these are a MUST),
By all means ultra sonic clean the carbs. But don't bother trying to clean/ultra sonic or solvent clean the Slow jets, they are just too tiny.
NEW Slow Jets "#42" were a MUST for me, & instantly it produced a steady tickover!
[some sources say "#38" Slow Jet, but go for #42].
Set Pilot Jets to "1+1/2 turns out" from closed.
For top-end running, I increased the Main Jets to "#95" (from #90) to cure the lean running.
I left the Needles and clip positions unchanged, middle pos'n#3
[I bought my Jets from SCI www.siriusconinc.com   - before DSS & CMSNL had anything]

One final piece of advice, DO keep the set of four carb bodies all linked together as one assembly; you can still work on each carb, alongside each other.

Oh & after many grazed knuckles, I could get that bank of carbs out and back into the bike within 2 hours! (just don't ask me 'how' now!)

Good luck & persevere!

[keithtraffic]

Thanks All.

Andy, what's the problem with splitting the carbs - I can see that splitting all four is a problem as it is necessary to remove the choke assys but is there an issue in splitting them 2 and 2. I am not sure that all four will fit into my ultrasonic cleaner and I do want to give them a good clean.

[simonc]

I think what Andy is saying is you don't need to split carbs, remove  all the smaller parts jets etc and float bowls all will fit in small ultrasonic bath.  I tend not to split unless I have to,   I use air for orifices in bodies,  clean clean clean

[deltarider]

I can't see why one would want to separate the carbs. The 'slow moving parts' do not wear, nor do they require maintenance. But, if you must... have to warn you... this is what you're $#@&!! looking at. Excuse my French. http://www.cb500four.com/fofo_cb500four/viewtopic.php?f=16&t=623

[andy_c101]

Thanks All.

Andy, what's the problem with splitting the carbs - I can see that splitting all four is a problem as it is necessary to remove the choke assys but is there an issue in splitting them 2 and 2. I am not sure that all four will fit into my ultrasonic cleaner and I do want to give them a good clean.

Keith,
I just didn't want the hassle of re-aligning the slider/choke linkage nor the fuel transfer lines/seals...

[keithtraffic]

Thanks all for the advice - will definitely see if I can get away with not separating them!

[keithtraffic]

The saga continues!

On closer examination, as well as weeping fuel from the bowl seals it became clear that there was a major issue with the seals for the fuel tubes between the carbs - the tubes were really loose and the seals were hardly doing any sort of job, so I decided I would have to separate the carbs to check them out and I have now confirmed that the seals are badly perished and will need to be replaced.

So now that the carbs are separated I have taken the opportunity to have them vapour blasted prior to reassembly and have brought the aftermarket refurb kits from David Silver as mentioned in my earlier posts (https://www.davidsilverspares.co.uk/parts/by-part-number/partnumber_PCRKCB550K3/)

But it seems nothing is ever simple with these carbs

The kits have arrived and the packaging identifies they are for the original carb part number 16100-404-004 which is the part number identified in the K3 parts list as being fitted to the K3 (so a good start). Having done a close visual inspection and a dimensional check as best I can, the parts seem to be the same as the original except that the hole pattern on the emulsifier tube is different to the original - does anyone know if this is critical - the patterns look quite specific so my first thought would be that they are there for a reason and should be the same? (I can post a pic if that would help).

The second problem is that, now the carbs are apart it seems that there are rubber 'O' rings fitted in groves as shown below (one each side of each carb), but I can't find any reference to them in the documentation I have - nor do they seem to appear on CMNSL or the K3 parts list - does anybody know about these - their sizes and a source (Once the carbs come back I can take one out and measure it but if there are no replacements available I don't really want to do this - although at least a couple of them look in a poor shape!

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Any further help on this welcome!

[Bryanj]

The only way to sort that is by measuring one im afraid

[Johnwebley]

Keith.

There is an engineering store called Hayley Group.

They supply O rings

Various sizes and qualities.

Check if you have one locally.

The Hereford branch is very helpful.

Used to be able to get stock over night.




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