What is this and why is it smoking?

What is this filter in the attached picture for? I couldn't find it in the Haynes manual I have. It has a connecting tube that runs down to the gearbox(?) and must pull air? But I have no idea.

Also, and a bigger issue, why does it smoke when the bike is warm?

 

That is your crank case breather vent. It at one time was hooked up to the airbox. The smoke can be from blow by. Do a compressions check.

 

Keep in mind that the reason it was hooked up to the air box was for PCV. That vent hose is normally supposed to pull gases from the crankcase back into the intake to be reburned.

That's why I kind of laugh when I see these little filters that people put on them after converting to pods. Those filters are filtering gases getting blown into the atmosphere, not filtering air going into the crankcase.

It would make perfect sense that this smokes a bit, just as you would see a bit of smoke if you open the oil filler while the engine's running. If it's smoking a lot, that may be more of a cause for concern.

 

They used to call it a road tube, before 1964.
Cars would just spew onto the road.
We were so unevolved !

 

up until 2007 diesels still had draft tubes puffing away and dripping oil.

i put a filter on mine to keep the bugs from making a nest in the hose and clogging it, otherwise SQL is correct its not filtering anything.

 

Its filtering out the bugs while it sits in the garage.

 

Sweetness. I think I may need to do a compression check as it can smoke quite a bit when just sitting at idle.

Thanks for the replies.