what is small tube under airbox?

[streido]

Does anyone know what the 7-8" clear rubber tube that clips under the stock airbox is for? Does not go into airbox but comes out under it and looks like an overflow or drain tube for something? Has a plastic right angle bend at one end and the other has a bung/stopper in it. The bung/stopper end clips under air box, the right anle bend joins a tube going behind airbox.

Anyway my own is yellowed and dirty so I just cut a new piece of tube and fitted that. While I was doing it I noticed what looked like some old gearbox oil in the old tube, but it smelt of petrol?

Guess it is some kind of overflow, just wonder if anyone can confirm what is meant to overflow into it?

[sidthesloth]

It is to drain oil build up from the airbox. The oil comes from the crankcase ventilation into the airbox. You usually drain it when cleaning your filter, though I never see anything more than a slight amount in my bikes.

[streido]

Thats what I thought Sid but it doesnt seem to be part of the airbox at all? I opened up the airbox last night to look and the tube is not connected to it, it pushes into a small black tube that sits under the airbox. I too noticed what your talking about cos I also had a tiny amount of engine oil sitting in the bottom inside of the airbox, but this looked more like used gearbox oil, more yellow, smelled like petrol tho?

Im at work right now but will try get a better look tomorrow, its def not engine oil tho. Will smell my bottle of unused gear oil to see if that smell the same petrol way, if it is then I guess it must be some kind of overflow for the gear oil?

[sidthesloth]

The petrol smell is from the petrol from your carb, the oil is from the engine breather hose, but, if it is not connected to the airbox, then I am on the wrong track.

[streido]

I thought the same as you Sid, that it was a drain for the airbox, thats why I opened up my airbox last nite. The little oil in my airbox was normal dark/black color but oil in the tube is yellow/beige color, same color as my gear oil is. Was getting dark last nite so maybe I missed something but was pretty sure tube was not joined to airbox.

Going to investigate more at the weekend cos I use my scoot every week day for work so I got no rush to get it back together at weekends. Im pretty sure it was gear oil tho, just the smell of petrol off it confused me, maybe thats just how my gear oil smells tho.

[mono]

Gear oil can't get to your airbox in any way since there is simply no connection between the gearbox and the engine itself...

The oil from the crankcase ventilation that gets in the tube is transported as a mist of very small particles, and I guess that's purifying it a little, the heavyer black stuff never makes it to the tube and stays in your airbox. The gasoline smell is to be expected from anything you find near the carb, especially on small engines like these. (trust me, i've seen a lot of them) Depending on climate there can also be some water in the tube, making the stuff look like mayonaise...

Anyway, I wouldn't worry about it (there's nothing strange going on) and just drain the tube whenever it's full...

[streido]

Thanks mono, that could be the answer. I honestly did not see the tube was connected to the airbox, guess from your and Sids comments that it must be tho? If like you say that water can get in as well as oil and mix to make the mayonaise looking stuff then that would explain it. I have never noticed it having anything in it till I looked when I replaced the grubby looking tube. Sounds like a plausable explanation tho, so i'll buy that.

Will check it out properly at the weekend just to be 100% happy that that is def the cause.

Thanks.

[mono]

It only _looks_ like it's not connected to the airbox, but if you look closer you will see that the part where it clips to the airbox is in fact a simple kind of one-way valve : from the outside you can suck air through the tube from the airbox, but not the other way around.

This works as a drain since the air pressure in the airbox is pulsating when the engine is running. Each time the intake valve in the cylinder head closes there will be a pressure "spike" because of the inertia of the air that was flowing into the airbox, this will force all kinds of collected goo through this little plastic valve into the tube...

(The same inertia is also the reason that some gas/air mixture will "bounce" from the intake manifold back through the carb into the airbox and leave traces of gasoline over there...)