New CNS Carby: What is the 'Vent tube'?

Hello everyone,

I have purchased the new CNS style carby which is working great but I am still fine tuning.

Very little info on this carby although I have worked it out from my knowledge of carbys in general... except one thing.

The CNS has a nipple at the bottom of the fuel bowl at comes with a crappy hose attached. Inside the bowl this nipple extends up well above the fuel level so I am assuming that it is some sort of overflow. Where is it supposed to overflow to? all over my bike and engine? Grubee Inc says that it is a a 'Vent tube' and should be left open. I have seen a photo a while ago that shows this tube joining back up to another nipple which leads to inside the venturi. Grubee says this is not used.

Seems strange to have an this tube thing at all does anyone think it would be safe to block it up?

Other than that the CNS is a worthy upgrade. Much improved acceleration and stronger top end too although fuel consumption seems higher, maybe this will drop once it is fine tuned to perfection.

if it's poking up over the fuel level, I'd guess it is for fuel vapor. When you say 'venturi' are you referring to the air intake?

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Yeah there is a nipple that extends into the intake, Dellorto call it the venturi sorry. No Idea what this is for it seemed logical to join up the vapour vent to this before I knew what it really was for.

Ok so I'll leave the vent open and ignore the nipple into the intake.

Cheers.

It is a fuel overflow vent tube. The hose is supposed to hang down below the engine.

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"No such thing as a stupid question, just a stupid answer"

48cc Grubee Starfire Round Head......

Thank you for confirming my suspicions.

Great new carby

lol, I've never heard of an overflow tube like that. Learn something new every day

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Sorry i know this is an old thread but im haveing a similar problem.
Should the nipple to the venturi be blocked and then run the hose from the float bowl to atmosphere?
My carby kit came with a hose from the lower nipple to the npple in the venturi also. It runs fine but will not restart once it is hot.
Thanks steve

The tube should hang down so that any overflow will go onto the ground rather than on you're engine. The nipple in the venturi doesn't need to be blocked, I've run mine with and without having it blocked and I don't really see a difference. I think the purpose of that nipple is to inject something into the airflow, like nitris oxide. Not a good idea if you ask me, but that's the only purpose I can see for it.

Hey I just got an idea. With a fuel pump, and some kind of pressure regulation for it, you could use that nipple to run this carb as a throttle body inject set-up. Wouldn't that be cool?

Also:

Just a general maintenance tip for that carb. That filter will soak up oil, but you can't see it, so as I learned recently it can get so saturated that it will choke the engine. So if you start to experience any lack of power or poor performance, wash the filter with dish soap and hot water. Let it dry completely before you use it again.