I'm rebuilding a 85 Rebel and need help on converting the normal box air filter to an aftermarket cold air intake filter? There a hose that connect to it and I can't figure out what it's for and if it's even possible to do?
Welcome. I believe the hose you are referring to is probably the crankcase breather tube. Many that convert to a pod air filter put a smaller filter on the hose. Problem is, oily crankcase vapors accumulate on the inside of the breather filter where they can't be seen. If the filter gets clogged, pressure will build up to the point of blowing the left side oil seal and dumping the engine oil. Leaving the breather tube open risks sucking grit into the engine.
Since you have a first generation carb, you might be able to route the hose between the carb and engine. FYI, pod filters don't improve performance, and don't filter the air going into the engine as well as the stock filter does. They really aren't a good performance or engine longevity mod. But if that's the look you are going for.....
Keepin' all the left over parts. Gonna use 'em to build another bike!