Motorcycle Repair: 1979 Honda CB 750 - fouls #2 plug, honda cb 750, vent tube

Question
After the cycle sits for a few days, it fouls the #2 plug and runs rough.  

I noticed there is a black hose identical to the hose from gas tank to carb that isn't attached to anything at the top.  Should it be and could that be related?

Thanks!

Answer
That black tube may be a vent tube.  Should be 2 of those.  It appears #2 is either running with an incorrect mixture or perhaps the choke is sticky.  I would check the carbs first, and do a compression test to evaluate the condition of #2.

Good luck,  Jan