I just removed the bulky air filter system from my 70 Series II (w/triple SU setup) and replaced it with 3 separate air filters. The filters came with breather tubes, but I didn't install them. What do these breather tubes do and are they necessary on each air cleaner?

Without seeing fotos, I would think that instead of breather tubes, they are fuel drain tubes for any acumulated fuel resulting from spit back and yes they are important and should be directed away from anything hot

They take the place of the large diameter breather that goes from the front of the head to the air filter assembly. If you are clever, you should be able to cobble up some hose and tubing, and connect all 3 into a "manifold" and connect it up at the breather housing on the front of the head. The purpose is to create a slight negative pressure in the crankcase, sucking out the fumes that bypass the rings, and burns them up as you drive. It can also help prevent oil leaks.

Thanks -- that helps a lot.