Fuel tap on 82 550 maxim

I have an 82 550 maxim, the bike is in great shape with approx. 9,500 miles. When purchased owner said bike ran.But fuel tap only worked in prime position. When I got bike home I noticed the vacum hose was missing from the fuel tap. I assume the hose goes to an attachment on the manifold somewhere. If this hose were in place would the fuel tap work as intended? As is the bike can be started, but is very tuff to keep running. My question is replace the fuel tap, or just the soe? Where do I find parts like these?