Hi all,
1991 CBR1000f, This tube was just kind of sitting there unconnected to anything when I removed the gas tank. The first pic is the upper part, and you can see it has a plastic connector in it. The second pick is the bottom of it, and it seems like it pokes out underneath the bike as if to drain something. Third pick is roughly where it was found on the right side of the bike along the crankcase and up into under the tank. Last pic is just for scale so you can see the length. For the life of me I can't figure out what its connected to. I've looked everywhere. It doesn't seem to connect to the bottom of the tank. I scoured the parts schematics online, and I can't find it there either. Please help! Thanks, Dave.

 

Pictures are to small. Looks like it might be a hose left behind for doing a carb sync. Attaches to little vacuum nipples on the intakes. Only guessing though.

 

^ Or someone did connect it to a vacuum port and was running with a vacuum gauge because they liked to see the needled moving while riding.
By the looks of it, more likely it was connected to a vacuum gauge, the was it is run and the length. That would allow a gauge to be tie-warped somewhere up top.

 

Think I figured it out. Under the tank theres a rubber funnel-looking thing that catches gas if you overfill the tank. Pretty sure this tube attaches to this "catch" and drains rthe fuel to the ground.

Thanks for the suggestions.

 

That is correct

 

At first I thought it was that drain tube but the factory one had a square shaped funnel part that slid over the tank nipple.
Those connectors you have at each end are not factory.
Yes there should be a factory overflow tube but, either someone replaced it, modified it or that tube was used for something else.