Fuel dumping

It would seem to me that you must have a float inside your carburator that is stuck open. This would allow the fuel to flood the carburator and come out the drain line that you are talking about. I would turn the fuel off at the tank, drain the fuel bowl, and then remove the fuel bowl to inspect the float to see just what is causing it to stick.
Ride Safe-Be Happy

Floats

You may have a stuck carburetor float or valve. If they have not been worked on the adjustment should be OK. So dirt or gum may be the problem. Removing cleaning the carburetor and adjusting may be necessary. You might try some carburetor cleaner. I would try a half can of Sea Foam to a tank of new gas. See if it loosens anything up. If not sounds like you will need help. I believe there are some cleaners you can spray in the float chamber if you can remove the fuel line.

Wonder if the bike sat for a while?
Dave

deffnently you have a stuck, maladjusted float, or heaven forbid a bad needle valve (float valve) in one or both of the carbs. If I am not mistaken there is a drain screw on the bottom of the float bowls. Try draining these and see if any dirt comes out.
good luck
Doug

Same thing mine is doing. It sat all winter and I used StaBil and dry gas and ran it so it was thru the carbs. Can you drain the bowls while they are still in the bike?

ETA Mine is an 1100. Does the 650 have two carbs also?