Honda-SOHC
SOHC.co.uk Forums => CB650 => Topic started by: Rally011 on October 27, 2026, 09:36:27 AM
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Hi Folks I hope someone can help.Im struggling with three fuel connections, the two rubber pipes are fuel I believe, and when you blow down the larger it returns up the slightly smaller pipe. Perhaps this just need a fuel tap with a flow and retur/ (Not Sure)
The other picture shows a brass connector, anyone know what this is and what I connect to it and where it should go? Or do I just put a rubber pipe on and blank it?
The bike is the CB650 SOHC, it does not have the large air box any more just the foam filters.1981 any help would be great PS I didnt take this bike apart 🙁
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Hello
Welcome to the site. :) I think you first need to do five posts before you can post a picture, but whatever, there is a mountain of experience here to help you.
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No images viewable, yet.
Could be supply and breather, possibly a vacuum line (some bikes in that era were changing to this type) which is used to switch the fuel tap on/off when engine is running.
Welcome to the forum Rally011.
As above, get to five posts and we can see images to help.
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Thanks for the reply. The part number of the fuel tap is 16950-461-771, and I believe its gravity feed. I will try and get a photo posted
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As I cant add photos downs anyone have any photos they can add?
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That fuel tap looks conventional and nothing unusual about it. Single outlet for fuel seems about all that's there.
Not many 650 SOHC around for people to have images, I'd guess. But a few more post should unlock that capability for you to add here.
Helpful would be image of where the pipes in question are coming from on the carburettors, then we can hopefully give better details to assist.
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I guess I will just have to reply to myself :)
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one more?
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A few pictures
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another
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another
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another
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A number of things can change around this model era, which bike do you have ? Is it early conventional style or the custom type with "peanut" tank shape ? Can you put a picture of it.
They are CV carbs in images (early model were PD in my understanding) and may have an alternative fuel tap design.
CV type moved, in some cases to Vac tap as different models had no overflow route from float bowls. They MAY have an accelerator pump too, with need for fuel supply.
Apologies for clunky explanation, these are not so common to discuss in comparison to other SOHC carbs.
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the Model I understand is a CB650B imported from the USA
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Schematic available for the B model confirn there's 3 pipes involved, but not where they go to.
The two black fuel lines appear to be on the same distribution bar across the 4 carbs, but may have a manifold missing to connect with single fuel outlet tap.
Ideally it needs someone with more in depth direct model experience to quantify as doesn't appear available in public availzble schematic.
If the odd brass outlet were a breather, that would need something on the tank above maximum fuel level to facilitate it without leaking.
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I think someone has fitted a vacuum fuel tap, maybe the tank was changed for a later design and the old tap didn’t fit. It looks as though to get the tap to work they fitted a vac gauge adapter into the vac screw fitting and used that for the fuel tap. The other pipes look standard. Has the fuel tap got one or two fuel pipe outlets?
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I’ve just ordered a new tap 16950-461-771 this has one outlet this should fit on the large hose just not sure what to do with the other two
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Looking at the parts list you appear to be missing a part described as an auto fuel cock part number 16970-460-731. This acts like a vacuum operated fuel tap in that it only allows fuel to flow when the engine is running. The brass nozzle is the vacuum take off, your missing the pipe. The other 2 fuel lines connect to this auto fuel cock and a final pipe connects that to the fuel tap.
Post a full pic of the carb bank so we can see if it’s missing.