Drain hose under the motor

[nwtk2007]

What is the little hose pointed down directly beneath the motor?

[cross]

What is the little hose pointed down directly beneath the motor?

The one in the back with a plug in it? It could be the oil catch tank drain hose.
If you look behind the motor and above the swing arm, should be small plastic tank that collects fluid from the crankcase breather. Crankcase vents into the air filter box and air filter box drains into that little tank.
There should be another fuel drain hose from the carbs as well

[EMS]

If you have a 1980-1982 or a 1979 with a vacuum petcock retrofit, it could be the vent hose from the valve.

[daves79x]

Originally, that cluster of hoses contained: Carb drain hose, airbox catch tank drain, and battery vent hose. The '80-'82 also had a carb drain on the left side, mounted to a clamp on the sump cover.

Dave

[nwtk2007]

Thanks guys. I found an online manual for my 1982 and it's a part of the emissions set up to prevent crankcase fumes from being sent into the engine and thus the exhaust. This bog takeaway being that if there is a little oil from that dripping out, it's not a big worry.

[cross]

True but take the plug out and drain it from time to time.

[sixinoz]

To add to this post, am I correct in saying that the drain tube plug is essential for the crankcase ventilation system to function correctly?
On a closed system the higher the revs the higher the crankcase pressure but reduced by the additional intake flow through the carbs.
With no plug air will be sucked back through the drain tube and only some from the crankcase thus causing an increase in crankcase pressure.
Possibility of oil leaks from this?

[Larry Zimmer]

Not certain about the affect on crankcase pressure. What you are saying sounds plausible. However, without the plug, the engine will suck a quantity of unfiltered air. That catch-bottle/drain line is connected to the air box down-stream of the air filter.
Another bit -- often that air bottle can be found to crack at the mounting tab where it is attached to the frame. Next time the rear wheel has been removed. inspect the catch bottle at the attaching tab. Even if completely broken at that point, the bottle will remain in position being held by the attached hoses. However, if cracked, it will leak considerably over time onto the frame and the right side swing arm pivot joint. (Does keep that seal pliable!) My fix was remove the bottle; repair the crack with epoxy and fiberglas; reinstall and add a large hose clamp around the bottle and frame to prevent vibration, and subsequent cracking.

[EMS]

Removing the plug will not result in an increase in crankcase pressure. Crankcase pressure is above atmosphere air pressure, which you have outside the plug. Therefore, there will always be more crankcase scavenging than sucking air in through the open tube.

[nwtk2007]

There is no plug on this hose. Could the lack of a plug cause the engine, after initially running, to be unable to start after cooling??

[cross]

I don't think so.
Describe your problem into detail. I'm sure someone on here will chime in

[daves79x]

Are you sure it’s not the carb drain hose? Very easy to tell.

Dave

[cross]

Without a picture it's hard to tell.
I don't think that any of those hoses whether plugged off or not would cause hard starting would it?

[EMS]

I bet it is the vacuum valve vent hose.

[Larry Zimmer]

What EMS mentioned is, certainly, a 'could be'. Good to check all 'open' hose ends occasionally. Mud-daubers like to build their little breeding grounds up inside the ends of things like small hoses. Makes a good plug!