blowing a greenish liquid into air box

hello i am new to bikes and just aquired a 1982 yamaha 750, this is my problem, i just rebuilt the carbs and put them on and fired the thing up for the first time, this bike has sat for around 5 yrs, it was smoking like a cheap cigar, then it started to blow a greenish looking liquid, almost like an oil, gas, water mixture into the air filter box, now the port it is blowing from has a hose that goes to the transmission i would guess just to the rear of the shift pedal, what is cauing the blow back and what could it be that is blowing out besides gas?

 

<guess mode on>
I'm thinking that the hose from the transmission is really the case breather, and the green fluid is coolant leaked or leaking into the case from ??. The only gaseous fumes coming out of that hose should be a slight oil mist, but given the age and condition of the motor/bike, any number of seals or gaskets may be blown and leaking: Valve seals, base gasket, head gasket, etc etc, ad naseum.
<guess mode off>
Scott