Beginner question - 2 fuel hoses on Briggs & Stratton engine?

[jackmower]

Hi

I recently came into posession of an old Jonsered ride on lawn mower with a Briggs & Stratton 289707-1179E1 engine.
The mower is in terrible shape and has lot's of problems running, but I've been having a great time handling these one by one and making the engine (almost) run. I have absolutely no experience woring with engines (I am a programmer by trade) but I'm having endless fund learning as I'm going.
I have, among other things, taken the carburetor apart and cleaned it and replaced parts in this and other places.
Some parts I couldn't get where I live, so I made them myself from old hoses and stuff.

Anyway, I now have the mower almost working. It runs and does not quit after a while which has been a big problem. I only have one problem left now - gas is seeping into the oil tank.
I have read a lot about this problem and I am now trying out possible solutions.
In this process one ting puzzles me - why does my engine have TWO hoses running from the fuel tank?
One of them goes to the carburetor - this makes sense.
The other one - fixed just next to the first one at the bottom of the fuel tank - goes to ... nowhere. It just hangs down from the fuel tank, fixed to nothing and not closed off or anything. As far as I can see no fuel drips from it, though I can't be 100% sure.

Does anybody know what that second hose is doing?
It feels like this might be a stupid question to ask, but it just puzzles me.
And I'm thinking there's a slight chance it has something to do with my gas-in-oil problem...

 

[bertsmobile1]

The second hose is the air vent
If air can not get in the fuel can not get out .
Some have charcoal canisters on the air line while others run it to the manifold so it is a closed loop .
The "problem" is when the mower is not in use, fuel vapours can escape from the tank vent which will cause all life on the planet to be extinguished.
Fuel in the oil is caused by the float valve not cutting the fuel off.
In the old days there was an overflow tube so it dripped onto the floor and you smelt fuel when you walked past , realised there was a problem & fixed it .
Now days the overflow is internal so the fuel dribbles into the carb then into the engine then into the sump then destroys the engine .

 

[jackmower]

Thanks for your input!
I am much wiser now
But - I just cleaned the carburetor from inside out with carb cleaner and a toothbrush.
Every nook and cranny.
Shouldn't that have fixed any problem with valves and stuff?

So the air vent hose is just supposed to behanging down freely like that?
Is it possible to attach some shut-off valve or something to the end of the hose to avoid murdering Earth at least when the mower is not in use?

 

[StarTech]

Nope, But are welcome to come and scrub my shop floor with that toothbrush. But I might need to get Sarge to inspect afterwards.

That 289707-1179-E1 came with either one of several versions of the Walbro or a Nikki carburetor. Rubber tip needle valve do develop wear ring leading to leaks (some are only visible under magnification), needle seats can pit leading to leaks. The LMT 5 and 6 Walbro uses an all metal needle with a rubber seat. The rest uses a rubber tip needle valve.

Just note there is 6 different carburetor repair kits for this engine,which to use depends on which carburetor your have. Carburetor also need disassebly and deep cleaning. Old way was to use a dip cleaner and the latest is to simply use water, soap, and ultrasonics. Neither method is 100% at cleaning but the Ultrasonic cleaning is a lot safer for the carburetor and tech pus it usually does a better job of deep cleaning.

 

[jackmower]

My toothbrushing never impressed anyone - especially not my dentist - so I doubt I would pass inspection!

Checking now, I see my valve has a rubber tip. This clears up another puzzle as I was wondering why my needle didn't have any seat.

I took the carburetor apart as much as I could and soaked everything in carb cleaner overnight and then gave all parts a good rubbing with the brush.
Sounds from your description like I should have been more gentle and careful when cleaning.
So I probably either damaged something during cleaning or it's the rubber tip.

I have ordered a whole new carburetor now. Cheap one from China, so not much to loose. The part number fits, at least.
We will see how it goes.
Thanks to both of you for the input!