SG airbox question--mystery hose fitting

[Bergman16]

So I had the carbs off for cleaning, and got them back on--had a bit of trouble with the rear boots, one of which had shrunk a bit due to age, I guess, but I managed to get it all back on.

One mystery. After I got the big breather hose re-attached to the airbox, I saw there was another hose fitting to the right of it (facing forward on the bike). I'm not sure I ever saw a hose hooked up to that, and am not sure where the other end would go once I did. Here's a photo of one off Ebay with the mystery fitting in the red box.

What vents into here, if anything? So many of the other airboxes listed on Ebay had only a solid nut there.

What am I missing?

Thanks,

--Steve

[Radioguylogs]

Older bikes ('79 and prior?) utilized that fitting to accept a hose to vent the carb bowls.

Newer bikes ('80 and later?) did not use that fitting, so it was blocked with plastic in the molding process when the box was manufactured. You can drill out a newer box so it can be used on older bikes.

[bikerphil]

I don't have that single small fitting on any of my 79's nor have I seen a fitting in that position on the airbox before. ???. It is in the position of one of the screws that holds the manifold in.

[DiverRay]

The two black plastic "plugs" on either side of the box were the vent location for the early bikes. The large center is for the engine breather, and the one in the red square is NOT a stock fitting. It is probably being used to hold the inside parts of the breather in place, like the one on the other side. The breather has a diverter and four tubes to put the engine "air" into each carb inlet.

[Bergman16]

Thanks. I did see a reference to a carb vent in a manual when I was trying to figure it out. I’ll try to find and post the page—it’s in one that Catatonic Bug posted.

It’s odd because my bike was an entirely unmolested SG, at least in my experience so far, other than tank paint. I wonder if it had gotten damaged and an earlier airbox swapped in. Guess I will just plug it.

and the middle drive vent hose is just open on the end attached to the airbox clamp, right?

[Bergman16]

Here’s another 80 on EBay with the same fitting but on the other side (photo may be reversed tho?) That makes 3 SGs with this vent if you include mine.

https://www.ebay.com/itm/YAMAHA-80-X.../265031355337?

Unfortunately the bike is stored 2 hours away so I can’t examine closely but I know it’s the same as the one shown in the first post.

[Bax]

Its just a piece of tubing put over the threads and nut head for the distribution manifold mount.

Bax

[Bergman16]

So in the aftermarket manual Catatonic Bug has on his page, there's all kinds of confusing things.--extra hoses coming off the nipples between 1/2 and 3/4 carbs, plus reference to the carb breather hooking up in that spot. Page 144-150. I saw somewhere that some carbs had these other lines--were they to vent off possible vapor lock? it would make sense then they might end up at the airbox.

Anyway, I don't have those lines, so gonna plug that fitting and hope for the best.

[Bax]

My SG still had both the originals on it. I think Yamaha did that to keep the fuel lines from contacting the metal threads so any wear point would be avoided.

Bax

[Bax]