SOHC.co.uk Forums > CB750

PD carb query

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MarkCR750:
I've googled it a fair bit but can't find anything , I actually think they should be open to atmosphere, that's because of the way the alloy is moulded above the hole,  like a hood, really not sure though , I'll do some more googling.

royhall:

--- Quote from: MarkCR750 on May 28, 2016, 02:50:36 PM ---Please could someone with PD carbs have a look at their No1 carb and tell me if there should be a small brass blanking plug or similar in the small hole in the side of my carb, it's in the centre of the photo below and you can see a light coloured vapour mark on the carb body just below it, my tickover dropped earlier today, I just squirted carb cleaner in the small balance pipes in the back of the carb and it came out of that hole, it's never done that before! 😀.

PS I can see the same feature on the No2 carb, squirting carb cleaner in No2 does not result in it coming out of the side, so the question now is should it?, are these holes vents to atmosphere to achieve a balance between the intake and atmosphere?, maybe?, confused at present.



--- End quote ---


There is a piece of alloy that looks like a tube connector missing off yours. The butcher has been at work there. I will try and get a usable photo of mine if I can. It should defo be blanked and not leaking.

royhall:
Managed to find a picture of mine, you can just see the tube type alloy piece here. All 4 carbs have a similar thing between 1&2 and 3&4 that face each other and look like they were at one time connected with a pipe, these have a brass insert to blank them. Only carb 1 has this extra hose fitting on the outside. It is completely sealed and the casting has never been drilled. Hope that helps.


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MarkCR750:
Harrisluv from the US site has spoken, looks like its specific to the 77 model, thanks for your replies all
HARRISLUV
On the 77 PD carbs, there is no vent tubing between the carbs.  Instead, each carb has its own individual vent hole.  It's really tiny.  It should be clear and open.

royhall:
I don't agree with that. My carbs in that picture are PD41B circa 1977 F2. The later carbs are PD42B circa 1978 onwards (possibly K7 1977). The bodies on both the F2 & K7 are the same just the jetting is different. That nozzle casting on mine has never been drilled and is airtight. Defo not a vent of any kind, the vents I believe are the 4 inner tubes facing each other.

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