What is this on the carb?

[Fumbler]

I was checking the air filter on my Echo CS-330T when I noticed an itty bitty tube on the carb diaphram cover (circled in the pic). It looks like some sort of fitting.

I don't know a lot about the parts of a chainsaw...but my logical thinking says that if there's an open fitting then there should be something connected to it.

What exactly is the function of this little tube/fitting?
Is something supposed to be connected to it?

 

[Kneejerk Bombas]

Here's my guess.
They use the same carbs on several different models of tools. On many tools the diaphram cover is just vented with a little hole, but on others a tube is run to the air fliter. Stihl calls this the intellicarb, and the tube has the effect of leaning the carb a little when the filter gets dirty, so it still runs good.
Blowers don't use this system because the filters stay pretty clean. So they just let the tube hang there.

 

[Scandy14]

It looks like it could be where a primer bulb hose would attach.

 

[no longer collecting]

carb attachment.

Mike is right ...this is the atmospheric side of the diaphragm. It will let ambiant air to make equalization when the pump is under load. Some carb uses only a simple hole at the centre to achieve that purpuse other are equipped with a nipple with a hose that is runned to the air filter element. Not a big concern here.

 

[Gravely Grinch]

We haven't seen any of those saws at the shop for repair yet but I pulled the AF off of the saw on the showroom. Nothing attaches to that nipple, it's just a vent like Mike said.